@article{nokey,

title = {Dosimetric characterization of a 90Sr/90Y Pterygium applicator with radiochromic film and Monte Carlo simulations},

author = {Maryam Rahbaran and Shirin A Enger and Parminder S Basran},

url = {https://iopscience.iop.org/article/10.1088/1361-6560/ae24dc},

doi = {10.1088/1361-6560/ae24dc},

issn = {1361-6560},

year  = {2025},

date = {2025-12-09},

urldate = {2025-12-09},

journal = {Physics in Medicine & Biology},

volume = {70},

number = {245003},

issue = {24},

abstract = {Objective. β-emitting radionuclides such as 90Sr/90Y are widely used for treating benign and malignant lesions, particularly with surface applicators. Despite their clinical relevance, the three-dimensional dose distributions delivered by these applicators remain insufficiently characterized using Monte Carlo simulations, the gold standard for dose calculation. This study characterizes the 3D dose distribution of a commonly used 90Sr/90Y Pterygium applicator. Goals include generating accurate percent-depth-dose (PDD) curves and validating a custom irradiation setup using radiochromic film and Monte Carlo simulations to support accessible, reproducible, and precise radiobiology experiments.



Approach. A Monte Carlo dose calculation software based on Geant4 10.02.p02 was developed. The Amersham SIA 20 Pterygium applicator, a stacked setup of 30 EBT-XD GafChromic® films, and a film-cell irradiation configuration (film layer, cell monolayer, growth media) were modeled. Dose rate was averaged over the 8.2 mm-diameter active area on the surface in water for both the stacked film and film-cell setups. The source spectrum was also calculated. Experimental PDDs were generated by irradiating stacked films and compared to Monte Carlo results.



Main results. Measured and simulated PDDs agreed within 2% up to 2.6 mm depth. Surface dose rates were 28.30, 26.48, 21.23, and 22.76 cGy/s in water, in the film active layer, in the cell monolayer, and in the growth media, respectively—close to the manufacturer’s nominal 27 cGy/s.



Significance. A Monte Carlo-validated PDD curve was produced for the source using a stacked film setup with EBT-XD GafChromic® film. A custom film-cell irradiation configuration was characterized for future radiobiology experiments.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Beyond single-run metrics with CP-fuse: A rigorous multi-cohort evaluation of clinico-pathological fusion for improved survival prediction in TCGA},

author = {Juan Duran and Yujing Zou and Martin Vallières and Shirin A. Enger},

url = {https://www.sciencedirect.com/science/article/pii/S2666827025001720},

doi = {https://doi.org/10.1016/j.mlwa.2025.100789},

issn = {2666-8270},

year  = {2025},

date = {2025-12-01},

journal = {Machine Learning with Applications},

volume = {22},

number = {100789},

abstract = {Accurate prediction of progression-free survival (PFS) is critical for precision oncology. However, most existing multimodal survival studies rely on single fusion strategies, one-off cross-validation runs, and focus solely on discrimination metrics, leaving gaps in systematic evaluation and calibration. We evaluated multimodal fusion approaches combining histopathology whole-slide images (via Hierarchical Image Pyramid Transformer) and clinical variables (via Feature Tokenizer-Transformer) across five TCGA cohorts: bladder cancer (BLCA), uterine corpus endometrial carcinoma (UCEC), lung adenocarcinoma (LUAD), breast cancer (BRCA), and head and neck squamous cell carcinoma (HNSC) (N=2,984). Three intermediate (marginal, cross-attention, Variational Autoencoder or VAE) and two late fusion strategies (trainable-weight, meta-learning) were trained end-to-end with DeepSurv. Our 100-repetition 10-fold cross-validation (CV) framework mitigates the variance overlooked in single-run CV evaluations. VAE fusion achieved superior PFS prediction (Concordance-index) in BLCA (0.739±0.019), UCEC (0.770±0.021), LUAD (0.683±0.018), and BRCA (0.760±0.021), while meta-learning was best for HNSC (0.686±0.022). However, Integrated Brier Score values (0.066–0.142) revealed calibration variability. Our findings highlight the importance of multimodal fusion, combined discrimination and calibration metrics, and rigorous validation for clinically meaningful survival modeling.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Dosimetric evaluation of unlaminated radiochromic films exposed to an Americium-241 source using measurements and Monte Carlo simulations},

author = {Mélodie Cyr and Maryam Rahbaran and Nada Tomic and Shirin A Enger},

doi = {10.1002/mp.70001},

issn = {2473-4209},

year  = {2025},

date = {2025-10-27},

journal = {Medical Physics},

volume = {52},

number = {e70001},

issue = {11},

abstract = {Background: Radiochromic GafChromic film models are widely used in clinical settings for quality assurance during cancer treatment planning. Although these films are extensively studied in photon dosimetry, research on their application in α-particle dosimetry remains limited. With the growing use of α-particles in cancer therapy, it is important to establish film dosimetry protocols tailored to α-particles. Unlike photons, α-particles are charged, have a high linear energy transfer, and induce significantly greater biological damage, highlighting the need for specialized dosimetric approaches.



Purpose: This study aimed to evaluate the response of various unlaminated GafChromic film models including EBT3, EBT-XD, and HD-V2, irradiated with an 241Am α-particle source, with combined experimental film irradiation and Monte Carlo (MC) simulations.



Methods: In this study, unlaminated EBT3, EBT-XD, and HD-V2 film pieces were irradiated with an 241Am disk source at various exposure times within a dark box. A detailed comparison was performed across the three film models, focusing on uncertainties and relative dose errors. Film analysis was conducted using a custom Python script, extracting normalized pixel values from the green channel. Additionally, a MC-based user code was developed using the Geant4 simulation toolkit to model the 241Am source and calculate the dose rates in the active layers of the films and in water. The mean dose rates were also calculated in a 1 mm diameter region of interest. These simulated dose rates were employed to convert film exposure times into absorbed doses for both the active layers and water, establishing a reference dosimetry protocol for α-particles across the three radiochromic GafChromic film models.



Results: The mean dose rates within a 1 mm diameter circular region of interest in the active layers of the three unlaminated GafChromic film models were determined to be 3.77 ± 0.002 Gy/min for EBT3, 4.04 ± 0.0022 Gy/min for EBT-XD, and 4.25 ± 0.0017 Gy/min for HD-V2. When the film material was changed to water, the dose rate was increased 14.3% for EBT3, 19.2% for EBT-XD, and 15.0% for HD-V2, with EBT3 showing the closest match to water-equivalence. Calibration curves for each film model were generated by fitting a power function to their responses. Refinements to the dose range were necessary to achieve an uncertainty below the 5% threshold. Among the models, HD-V2 required the most adjustments to its dose range and exhibited the highest levels of experimental, fit, and total uncertainties, along with the largest relative dose errors.



Conclusions: This study investigated α-particle dosimetry protocols for unlaminated EBT3, EBT-XD, and HD-V2 GafChromic film models using experimental irradiations and MC simulations. Although EBT3 and EBT-XD demonstrate strong potential for α-particle quality assurance in treatment planning, the HD-V2 film model requires further investigation before it can be recommended for this application.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Quantifying geometric and dosimetric advantage from the use of rectal spacing in HDR prostate brachytherapy},

author = {Joel Beaudry and Tonghe Wang and David Aramburu Núñez and Marisa Kollmeier and Daniel Gorovets and Shirin A. Enger and Antonio L. Damato},

url = {https://www.brachyjournal.com/article/S1538-4721(25)00298-3/abstract},

doi = {10.1016/j.brachy.2025.08.009},

issn = {1538-4721},

year  = {2025},

date = {2025-10-17},

journal = {Brachytherapy},

abstract = {Introduction: Rectal spacers are used during prostate external beam radiation therapy to increase rectal-prostate separation, thereby reducing rectal dose and toxicity. However, their role in high-dose-rate (HDR) brachytherapy remains less understood. This paper presents (i) a cohort study evaluating the dosimetric impact of rectal spacers in HDR prostate brachytherapy and (ii) a simulation study assessing how rectal-prostate separation affects dosimetry.



Methods: We retrospectively analyzed 157 patients treated with 15 Gy HDR prostate boost brachytherapy. Patients were divided into preimplant spacer (n = 49) and nonspacer (n = 108) cohorts. Prostate and rectal dose-volume histogram (DVH) metrics were compared, and rectal-prostate separation was measured on intraoperative transrectal ultrasound. A custom linear programming optimizer simulated plans with separations of 0.5-12 mm in 30 nonspacer cases to evaluate resulting dose metrics.



Results: Mean (± standard deviation) rectal-prostate separation was 7.8 ± 1.4 mm with spacer versus 4.0 ± 1.4 mm without spacer. Rectal dose was significantly reduced with spacer (mean D2cc 7.4 ± 1.0 Gy vs. 9.2 ± 1.0 Gy; p < 0.001), while prostate coverage remained similar (mean D90 16.4 ± 0.3 Gy vs. 16.3 ± 0.3 Gy; p = 0.071). Simulations showed that separations > 3 mm consistently achieved prostate D90 > 16 Gy and V100 > 95%, and separations > 4 mm produced a marked reduction in rectal dose.



Conclusion: Rectal spacers significantly reduce rectal dose in HDR prostate brachytherapy. Patients with rectal-prostate separations of at least 4 mm are most likely to benefit.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Automatic catheter digitization in breast brachytherapy},

author = {Sébastien Quetin and Hossein Jafarzadeh and Jonathan Kalinowski and Hamed Bekerat and Boris Bahoric and Farhad Maleki and Shirin A. Enger},

url = {https://aapm.onlinelibrary.wiley.com/doi/10.1002/mp.18107},

doi = {https://doi.org/10.1002/mp.18107},

issn = {2473-4209},

year  = {2025},

date = {2025-09-12},

urldate = {2025-09-12},

journal = {Medical Physics},

volume = {52},

number = {e18107},

issue = {9},

abstract = {Background:

High dose rate (HDR) brachytherapy requires clinicians to digitize catheters manually. This process is time-consuming, complex, and depends heavily on clinical experience-especially in breast cancer cases, where catheters may be inserted at varying angles and orientations due to an irregular anatomy.



Purpose:

This study is the first to automate catheter digitization specifically for breast HDR brachytherapy, emphasizing the unique challenges associated with this treatment site. It also introduces a pipeline that automatically digitizes catheters, generates dwell positions, and calculates the delivered dose for new breast cancer patients.



Methods:

Treatment data from 117 breast cancer patients treated with HDR brachytherapy were used. Pseudo-contours for the catheters were created from the treatment digitization points and divided into three classes: catheter body, catheter head, and catheter tip. An nnU-Net pipeline was trained to segment the pseudo-contours on treatment planning computed tomography images of 88 patients (training and validation). Then, pseudo-contours were digitized by separating the catheters into connected components. Predicted catheters with an unusual volume were flagged for manual review. A custom algorithm was designed to report and separate connected components containing colliding catheters. Finally, a spline was fitted to every separated catheter, and the tip was identified on the spline using the tip contour prediction. Dwell positions were placed from the created tip at a regular step size extracted from the DICOM plan file. Distance from each dwell position used during the clinical treatment to the fitted spline (shaft distance) was computed, as well as the distance from the treatment tip to the one identified by our pipeline. Dwell times from the clinical plan were assigned to the nearest generated dwell positions. TG-43 dose in water was computed analytically, and the absorbed dose in the medium was predicted using a published AI-based dose prediction model. Dosimetric comparison between the clinically delivered plan dose and the created automated plan dose was evaluated regarding dosimetric indices percent error.



Results:

Our pipeline was used to digitize 408 catheters on a test set of 29 patients. Shaft distance was on average 0.70 ± 3.91 mm and distance to the tip was on average 1.37 ± 5.25 mm. The dosimetric error between the manual and automated treatment plans was, on average, below 3% for planning target volume V100, V150, V200 and for the lung, heart, skin, and chest wall D2cc and D1cc, in both water and heterogeneous media. For D0.1cc values in all the organs at risk, the average error remained below 5%. The pipeline execution time, including auto-contouring, digitization, and dose to medium prediction, averages 118 s, ranging from 63 to 294 s. The pipeline successfully flagged all cases where digitization was not performed correctly.



Conclusions:

Our pipeline is the first to automate the digitization of catheters for breast brachytherapy, as well as the first to generate dwell positions and predict corresponding AI-based absorbed dose to medium based on automatically digitized catheters. The automatically digitized catheters are in excellent agreement with the manually digitized ones while more accurately reflecting their true anatomical shape.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Development and characterization of a prototype selenium-75 high dose rate brachytherapy source},

author = {Jonathan Kalinowski and Oren Tal and Jake Reid and John Munro 3rd and Matthew Moran and Andrea Armstrong and Shirin A. Enger},

url = {https://aapm.onlinelibrary.wiley.com/doi/10.1002/mp.18088},

doi = { https://doi.org/10.1002/mp.18088},

issn = {2473-4209},

year  = {2025},

date = {2025-09-09},

urldate = {2025-09-09},

journal = {Medical Physics},

volume = {52},

number = {e18088},

issue = {9},

abstract = {Background:

75Se (t1/2 ≈ 120 days, Eγ,avg ≈ 215 keV) offers advantages over 192Ir (t1/2 ≈ 74 days, Eγ,avg ≈ 360 keV) as a high dose rate brachytherapy source due to its lower gamma energy and longer half-life. Despite its widespread use in industrial gamma radiography, a 75Se brachytherapy source has yet to be manufactured.



Purpose:

A novel 75Se-based source design with a vanadium diselenide core, titled the SeCure source, was proposed. This study aimed to evaluate the feasibility of this source design for dosimetry and manufacturability purposes and to develop an activated prototype source.



Methods:

The source was modeled and integrated into the Monte Carlo-based treatment planning system RapidBrachyMCTPS, where its TG-43U1 parameters, photon spectrum, and broad beam first half-value layers (HVL1) and tenth-value layers (TVL1) in lead, tungsten, and concrete were calculated. A prototype source was manufactured, and the vanadium diselenide content of the capsule was verified with neutron radiography. The source was then activated to a nominal activity of 8.5 ± 0.9 mCi at the McMaster Nuclear Reactor. The activity was measured with two separate dose calibrators. Gamma spectroscopy was used to characterize any activated radioactive contaminants in the source, and wipe testing was performed to check for any leakage of 75Se from the encapsulation.



Results:

The SeCure source's TG-43U1 parameters were computed, showing that 2.056 ± 0.003 times the activity of 75Se is required relative to 192Ir to achieve the same dose rate in water at (1 cm, 90°). The mean spectral energy of the source is 214.695 ± 0.005 keV, resulting in reduced first half-value and tenth-value layers relative to 192Ir in attenuating materials. For example, the HVL1 was reduced from 2.795 ± 0.002 mm to 1.020 ± 0.001 mm in lead, from 2.049 ± 0.002 mm to 0.752 ± 0.001 mm in tungsten, and from 70.63 ± 0.04 mm to 61.37 ± 0.03 mm in concrete. The activated source achieved the desired activity, indicated as 9.2 ± 0.2 mCi and 8.5 ± 0.9 mCi at the end of irradiation on the two dose calibrators. All identified radionuclide contaminants decaying below 0.1% of the 75Se activity after 5 days post-irradiation. Wipe testing only identified radioactive contaminants present in activated titanium, with only 1.24 ± 0.01 × 10−7 mCi of 24Na detected 72 h post-irradiation, indicating that the integrity of the encapsulation was maintained.



Conclusions:

The SeCure design possesses the dosimetric, spectral, and physical properties necessary for a feasible high dose rate brachytherapy source. Next, manufacturing of a high-activity SeCure source will be pursued.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Microdosimetry calculations in situ for clinically relevant photon sources and their correlation with the early DNA damage response},

author = {Mirta Dumančić and Jonathan Kalinowski and Victor D Diaz-Martinez and Joanna Li and Behnaz Behmand and Joseph M DeCunha and Shirin A Enger},

url = {https://aapm.onlinelibrary.wiley.com/doi/10.1002/mp.17979},

doi = {10.1002/mp.17979},

issn = {2473-4209},

year  = {2025},

date = {2025-07-15},

urldate = {2025-07-15},

journal = {Medical Physics},

volume = {52},

number = {e17979},

issue = {7},

abstract = {Background:

Radiobiological data suggests variations in relative biological effectiveness (RBE) between clinically used photon-based sources. A microdosimetric formalism using Monte Carlo (MC) methods can mechanistically describe the photon RBE. Experimentally derived RBE based on DNA double-strand breaks (RBEDSB) has been shown to scale with the microdosimetry quantity dose-mean lineal energy (yD).



Purpose:

To calculate microdosimetric spectra for clinically relevant photon sources, spanning from soft x-rays produced by a 50 kVp x-ray source through various brachytherapy sources up to a 6 MV medical linac. Furthermore, we investigated the correlation between RBEDSB and yD of different photon sources.



Methods:

Photon sources simulated include low-energy x-rays (50 kVp), orthovoltage x-rays (225 kVp), high-dose-rate brachytherapy sources (75Se, 192Ir and 60Co), and a 6 MV medical linac. Secondary electron spectra at the cellular level were calculated for in vitro cell irradiation setups using Geant4 MC-based packages, RapidBrachyMCTPS and RapidExternalBeam. The obtained spectra were used in MicroDose, a microdosimetry simulation software, to obtain microdosimetric quantities, including single-event lineal energy (y) and specific energy (z) spectra, and dose-mean and frequency-mean quantities (yF, yD, zsF, zsD). Uniform spherical targets (1–14 μm radius) and realistic HeLa and PC3 cell nucleus models were simulated using cell size data obtained from literature and nuclei size data from confocal microscopy imaging. Radiobiological experiments using γH2AX foci quantified DNA double-strand breaks for HeLa and PC3 cells after irradiations with 50 and 225 kVp, 192Ir, and 6 MV linac, and RBEDSB was determined using 225 kVp as the reference.



Results:

The calculated yD (yF) is within the 3.5–1.2 keV/μm range (1.8–0.2 keV/μm) for 1 μm simulated target size between the lowest energy 50 kVp x-ray source and the highest energy 6 MV linac source, respectively. For the HeLa and PC3 cell nuclei models based on microscopy data, yD (yF) spans from 1.6 to 0.6 keV/μm (0.7 to 0.2 keV/μm). When compared between different target sizes, yD (yF) ranges from 3.5 to 1.0 (1.8–0.4) keV/μm between 1 and 10 μm radius targets for the 50 kVp x-ray source. A smaller change is observed for 6 MV linac, ranging from 1.2 to 0.5 keV/μm and 0.23 to 0.22 keV/μm for yD and yF, respectively. For the simulated 75Se source currently under investigation, the calculated yD values are 11%–24% higher relative to those of 192Ir in the range of target sizes between 1 and 14 μm in radius. RBEDSB for HeLa cells was 1.4 ± 0.7 for 50 kVp x-rays, 0.5 ± 0.2 for 192Ir, and 0.7 ± 0.4 for 6 MV linac irradiations. For PC3 cells, RBEDSB was 1.3 ± 0.6, 0.8 ± 0.4 and 0.5 ± 0.3 for 50 kVp, 192Ir and 6 MV linac, respectively. Measured RBEDSB values are consistent with yD ratios of the corresponding photon sources for HeLa and PC3 nucleus models.



Conclusions:

Microdosimetric spectra strongly depend on the simulated energy of photon sources and target size, with yD and zsD decreasing by a factor of ≈2–3 between diagnostic 50 kVp and 6 MV therapeutic x-rays for target sizes from 1–14 μm in radius. The early damage RBEDSB indicates this stochastic change in energy density between various photon sources as the yields of γH2AX foci per nucleus scale with yD of the source.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Monte Carlo-based dosimetry and optimization of a custom alpha cell irradiation setup},

author = {Maryam Rahbaran and Joanna Li and Shirin A. Enger},

url = {https://iopscience.iop.org/article/10.1088/1361-6560/ade846},

doi = {10.1088/1361-6560/ade846},

issn = {1361-6560},

year  = {2025},

date = {2025-07-03},

journal = {Physics in Medicine & Biology},

volume = {70},

number = {135011},

issue = {13},

abstract = {Objective.When combined with targeting agents,α-particle-emitting radionuclides show promise in treating hypoxic tumors and micrometastases. These radionuclides exhibit a high relative biological effectiveness (RBE), attributed to their high linear energy transfer, and induce complex DNA damage within targeted cells. However, most clinical experience and radiobiological data are derived from photon irradiation. To optimizeα-particle-based treatments, further research is needed to refine their RBE estimates. This study aimed to characterize and optimize a customin-vitrocell irradiation setup forα-particle RBE studies using241Am through Monte Carlo simulations.Approach.A Geant4-based Monte Carlo simulation model was used to simulate a custom cell well setup. An241Am (48 kBq) source was positioned beneath the well with an adjustable source-to-surface distance (SSD). The spectra of decay products was calculated with 6.5×109simulated241Am decay events. Simulations were conducted for SSD values of 2 mm, 5 mm, and 7 mm under three scenarios: (A) total dose rate from all decay products, (B) excludingγ-emissions, and (C) excluding secondary particles. Results were compared to published spectra and a published dose rate (0.1 Gy min-1) as validation.Main results.The validation dose rate was 0.1136 Gy min-1. Photons of 13.9-59.5 keV andα-particles of 5.39-5.48 MeV were observed. The dose inhomogeneity across the cells was around 30%, 10%, and 5% in the 2, 5, and 7 mm SSD setups, respectively. The corresponding total dose rates in cells for the three SSDs were 0.583, 0.146, and 0.0830 Gy min-1. The dose rate contributions were 90% fromα-particles, less than 0.07% fromγ-emissions, and 9%-10% from secondary particles.Significance.To accurately assess radiobiological effects, it is important to consider the full decay spectrum of radionuclides and their secondary particles in dosimetry calculations. These findings will aid in refining experimental setups for futurein-vitrostudies, contributing to more reliable RBE calculations.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Tumour nuclear size heterogeneity as a biomarker for post-radiotherapy outcomes in gynecological malignancies},

author = {Yujing Zou and Harry Glickman and Manuela Pelmus and Farhad Maleki and Boris Bahoric and Magali Lecavalier-Barsoum and Shirin A. Enger},

url = {https://www.phiro.science/article/S2405-6316(25)00098-3/fulltext},

doi = {10.1016/j.phro.2025.100793},

issn = {2405-6316},

year  = {2025},

date = {2025-07-01},

journal = {Physics and Imaging in Radiation Oncology},

volume = {35},

number = {100793},

abstract = {Background and purpose: Radiotherapy targets DNA in cancer cell nuclei. Radiation dose, however, is prescribed to a macroscopic target volume assuming uniform distribution, failing to consider microscopic variations in dose absorbed by individual nuclei. This study investigated a potential link between pre-treatment tumour nuclear size distributions and post-radiotherapy outcomes in gynecological squamous cell carcinoma (SCC).



Materials and methods: Our multi-institutional cohort consisted of 191 non-metastatic gynecological SCC patients who had received radiotherapy with diagnostic whole slide images (WSIs) available. Tumour nuclear size distribution mean and standard deviation were extracted from WSIs using deep learning, and used to predict progression-free interval (PFI) and overall survival (OS) in multivariate Cox proportional hazards (CoxPH) analysis adjusted for age and clinical stage.



Results: Multivariate CoxPH analysis revealed that a larger nuclear size distribution mean results in more favorable outcomes for PFI (HR = 0.45, 95% CI: 0.19 - 1.09, p = 0.084) and OS (HR = 0.55, 95% CI: 0.24 - 1.25, p = 0.16), and that a larger nuclear size standard deviation results in less favorable outcomes for PFI (HR = 7.52, 95% CI: 1.43 - 39.52, p = 0.023) and OS (HR = 4.67, 95% CI: 0.96 - 22.57, p = 0.063). The bootstrap-validated C-statistic was 0.56 for PFI and 0.57 for OS.



Conclusion: Despite low accuracy, tumour nuclear size heterogeneity aided prognostication over standard clinical variables and was associated with outcomes following radiotherapy in gynecological SCC. This highlights the potential importance of personalized multiscale dosimetry and warrants further large-scale pan-cancer studies.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {A data-driven approach to model spatial dose characteristics for catheter placement of high dose-rate brachytherapy for prostate cancer},

author = {Björn Morén and Hossein Jafarzadeh and Shirin A Enger},

url = {https://www.sciencedirect.com/science/article/pii/S0010482525003713?via%3Dihub},

doi = {https://doi.org/10.1016/j.compbiomed.2025.110020},

issn = {1879-0534},

year  = {2025},

date = {2025-05-01},

journal = {Computers in Biology and Medicine},

volume = {190},

number = {110020},

abstract = {Background: High dose rate brachytherapy (HDR BT) is a common treatment modality for cancer. In HDR BT, a radioactive source is placed inside or close to a tumor, aiming to give a high enough dose to the tumor, while sparing nearby healthy tissue and organs at risk. Treatment planning of HDR BT for prostate cancer consists of two types of decisions, placement of catheters, modeled with binary variables, and dwell times, modeled with continuous non-negative variables. Optimal spatial placement of catheters is important for avoiding local recurrence and complications, but such characteristics have not been modeled for the combined treatment planning problem of catheter placement and dwell time optimization.



Method: We propose a data-driven approach using linear regression, mutual information, and random forests to find convex estimates of spatial dose characteristics that correlate well with contiguous volumes receiving a too-high (hot spots) or too-low dose (cold spots). These estimates were incorporated in retrospective treatment plan optimization of 28 prostate cancer patients.



Results: The proposed hot-spot terms reduced the volume receiving twice the prescribed dose by 29% at 14 catheters. Also, the results illustrate the trade-offs between the number of catheters and spatial dose characteristics.



Conclusions: Our study demonstrates that incorporating a term for hot spots in the objective function of the treatment planning model is more effective in reducing hot spots than catheter placements that are not optimized for hot spots.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Dosimetric impact of positional uncertainties and a robust optimization approach for rectal intensity-modulated brachytherapy},

author = {Björn Morén and Alana Thibodeau-Antonacci and Jonathan Kalinowski and Shirin A. Enger},

url = {https://aapm.onlinelibrary.wiley.com/doi/10.1002/mp.17800},

doi = {10.1002/mp.17800},

issn = {0094-2405},

year  = {2025},

date = {2025-03-31},

journal = {Medical Physics},

volume = {52},

issue = {6},

pages = {3528–3540},

abstract = {Background: Intensity-modulated brachytherapy (IMBT) employs rotating high-Z shields during treatment to decrease radiation in certain directions and conform the dose distribution to the target volume. Prototypes for dynamic IMBT have been proposed for prostate, cervical, and rectal cancer.



Purpose: We considered two shielded applicators for IMBT rectal cancer treatment and investigated how rotational uncertainties in the shield angle and translational uncertainties in the source position affect plan evaluation criteria.



Methods: The effect of rotational errors of 3∘ , 5∘ and 10∘ , and translational errors of 1, 2 and 3 mm on evaluation criteria were investigated for shields with 

180

∘

 and 

90

∘

 emission windows. Further, a robust optimization approach based on quadratic penalties that includes scenarios with errors was proposed. The extent to which dosimetric effects of positional errors can be mitigated with this model was evaluated compared to a quadratic penalty model without scenarios with errors. A retrospective rectal cancer data set of ten patients was included in this study. Treatment planning was performed using the Monte Carlo-based treatment planning system, RapidBrachyMCTPS.



Results: For the largest investigated rotational error of 

±

10

∘

 , the clinical target volume 

D

90

 remained, on average, within 

5

%

 of the result without error, while the contralateral healthy rectal wall experienced an increase in the mean 

D

0.1

c

c

 , 

D

2

c

c

 , and 

D

50

 of 

26

%

 , 

9

%

 , and 

1

%

 for the 

180

∘

 shield and of 32%, 9%, and 2% for the 

90

∘

 shield. For translational errors of 

±

2

 mm, there were increases in dosimetric indices for both the superior (sup) and inferior (inf) dose spill regions. Specifically, for the 

180

∘

 shield, the 

D

0.1

c

c

 , 

D

2

c

c

 , and 

D

50

 increased by 

13

%

 , 

11

%

 , and 

10

%

 , respectively, for the sup region, and by 

26

%

 , 

15

%

 , and 

11

%

 , respectively, for the inf region. Similar results were obtained with the 

90

∘

 shield. Overall, the robust and traditional models had similar results. However, the number of active dwell positions obtained with the robust model was larger, and the longest dwell time was shorter.



Conclusions: We have quantified the effect of rotational shield and translational source errors of various magnitudes on evaluation criteria for rectal IMBT. The robust optimization approach was generally not able to mitigate positional errors. However, it resulted in more homogeneous dwell times, which can be beneficial in conventional high-dose-rate brachytherapy to avoid hot spots around specific dwell positions.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Isolating the impact of tissue heterogeneities in high dose rate brachytherapy treatment of the breast},

author = {Jules Faucher and Vincent Turgeon and Boris Bahoric and Shirin A. Enger and Peter G. F. Watson},

url = {https://www.phiro.science/article/S2405-6316(25)00042-9/fulltext},

doi = {10.1016/j.phro.2025.100737},

issn = {2405-6316},

year  = {2025},

date = {2025-01-01},

journal = {Physics and Imaging in Radiation Oncology},

volume = {33},

number = {100737},

abstract = {Background and purpose: Clinical brachytherapy treatment planning is performed assuming the patient is composed entirely of water and infinite in size. In this work, the effects of this assumption on calculated dose were investigated by comparing dose to water in water (Dw,w) in an unbound phantom mimicking TG-43 conditions, and dose to medium in medium (Dm,m) for breast cancer patients treated with high dose rate brachytherapy.



Materials and methods: Treatment plans for 123 breast cancer patients were recalculated with a Monte Carlo-based treatment planning software. The dwell times and dwell positions were imported from the clinical treatment planning system. The dose was computed and reported as Dw,w and Dm,m. Dose-volume histogram (DVH) metrics were evaluated for target volumes and organs at risk.



Results: Dw,w overestimated the dose for most studied DVH metrics. The largest median overestimations between Dm,m and Dw,w were seen for the planning target volume (PTV) V200% (5.8%), lung D0.1 cm 3 (6.0%) and skin D0.1 cm 3 (4.2%). The differences between Dm,m and Dw,w were statistically significant for all investigated DVH metrics. The PTV V90% had the smallest deviation (0.7%).



Conclusion: There was a significant difference in the DVH metrics studied when tissue heterogeneities and patient-specific scattering are accounted for in high dose rate breast brachytherapy. However, for the studied patient cohort, the clinical coverage goal (PTV V90%), had the smallest deviation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Cyr2024-me,

title = {Establishing a standardized murine orthotopic intra-rectal model for the study of colorectal adenocarcinoma},

author = {Mélodie Cyr and Naim Chabaytah and Joud Babik and Behnaz Behmand and Guillaume St-Jean and Shirin A. Enger},

url = {https://jgo.amegroups.org/article/view/93989},

doi = {10.21037/jgo-24-515},

isbn = {2078-6891},

year  = {2024},

date = {2024-12-31},

urldate = {2024-12-31},

journal = {Journal of Gastrointestinal Oncology},

volume = {15},

issue = {6},

pages = {2578-2587},

abstract = {Background: Orthotopic models offer a more accurate representation of colorectal cancer (CRC) compared to subcutaneous models. Despite promising results from the reported intra-rectal models, establishing a standardized method for CRC research remains challenging due to model variability, hindering comprehensive studies on CRC pathogenesis and treatment modalities, such as brachytherapy. This study aimed to establish a standardized workflow for an orthotopic intra-rectal animal model to induce the growth of colorectal adenocarcinoma in male and female mice.



Methods: HT-29 colorectal adenocarcinoma cells were injected into the rectal mucosa of female (n=21) and male (n=26) non-obese diabetic severe combined immunodeficiency (NOD SCID) gamma (NSG) mice. Mice were placed on a 45° wedge elevating their pelvis for better visualization of the anus. Tumor growth and localization were monitored using a 7-T magnetic resonance imaging (MRI) scanner with rapid acquisition with relaxation echo (RARE) sequence at weeks 1, 2, and 3 post-cell instillation. Once tumors reached 5-8 mm in diameter, the mice were euthanized. Histopathology and immunohistochemical analyses confirmed the tumors' morphology, including necrosis, vascularity (CD-31) and apoptosis (cleaved caspase-3).



Results: There was a 92% and 95% tumor growth success rate in male and female mice, respectively. Tumors grew to 5-8 mm in diameter within ~20 days. No significant difference in tumor size was observed between genders. Tumor morphology was consistent across cases. Most tumors exhibited a lack of central blood vessels, accompanied by varying degrees of necrosis and apoptosis, whereas external portions were highly vascularized.



Conclusions: An orthotopic intra-rectal model was successfully developed. This model will be used in future studies to evaluate the efficacy of CRC treatments.



Keywords: Colorectal adenocarcinoma; HT-29; animal model; orthotopic intra-rectal.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Rahbaran2025-gg,

title = {RapidBrachyIVBT: A dosimetry software for patient-specific intravascular brachytherapy dose calculations on optical coherence tomography images},

author = {Maryam Rahbaran and Jonathan Kalinowski and Joseph M. DeCunha and Kevin J. Croce and Brian A. Bergmark and James M. G. Tsui and Phillip M. Devlin and Shirin A. Enger},

doi = {https://doi.org/10.1002/mp.17462},

issn = {2473-4209},

year  = {2024},

date = {2024-11-19},

journal = {Medical Physics},

volume = {52},

issue = {2},

pages = {1256-1267},

abstract = {Background

Large reported variability in the material composition and geometrical components of the Xoft electronic high dose rate brachytherapy causes inter-source discrepancy in the source output. This variability is due to the manual manufacturing and assembly of the sources.



Purpose

This study aimed to develop a dosimetry software tool called E-Brachy to characterize the Xoft source and quantify the discrepancies in its photon spectrum and dosimetric properties.



Methods

E-Brachy is based on the Geant4 Monte Carlo toolkit and consists of two parts. In part one, the geometry and material composition for the source received in the computer-aided design format from the vendor were converted to the geometry description markup language format using the GUIMesh Python tool and integrated into the E-Brachy software. There was a large variation in material composition and thickness for some of the tube components. The simulation started from electrons and resulted in x-ray generations in the anode region. Multithreading, a track length estimation, and the uniform bremsstrahlung splitting variance reduction techniques were used to decrease the simulation time and increase the x-ray production. The photon energy, position, and momentum were saved into a phase space file as the photon exited the source, but before interacting with the external environment. The obtained x-ray energy spectrum was compared with measurements from the National Institute of Standards and Technology (NIST). In part two, by sampling from the generated photons, the dose rates and dosimetric parameters according to the TG-43 protocol were calculated for model S7500 and compared to the ones previously calculated for model S700 source, which were deemed identical by the manufacturer.



Results

The material composition that resulted in the most similar spectrum as the measured NIST spectrum with Pearson's correlation coefficient of 0.99 and a calculated Euclidean difference of 

 keV was chosen for further dosimetric analysis of the model S7500 source. Characteristic peaks showed the presence of tungsten, yttrium, and silver in the source components. Differences in dose rates between the two source models surpassed 20% for polar angles 

, reaching a peak at 

 cm and 

. The differences in the radial dose function values were within 5%. The relative difference in percentage between the anisotropy function values of the two models was closer to 0 for smaller 

 values, but at higher polar angles, they increased to 300%.



Conclusions

A software package called E-Brachy was successfully developed for the characterization and dosimetry of Xoft electronic brachytherapy sources. E-Brachy can be combined with spectral measurements to investigate the inter- and intra-source variability. The software package was tested by comparing the simulated spectra from the S7500 Xoft source model with NIST measurements and its TG-43 parameters with the S700 model. The TG-43 parameters between the two sources significantly exceed the recommendations of TG-56.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{Esmaelbeigi2025-ww,

title = {E-Brachy: New dosimetry package for electronic brachytherapy sources},

author = {Azin Esmaelbeigi and Jonathan Kalinowski and Nada Tomic and Mark J. Rivard and Te Vuong and Slobodan Devic and Shirin A. Enger},

url = {https://aapm.onlinelibrary.wiley.com/doi/10.1002/mp.17462},

doi = {10.1002/mp.17462},

issn = {2473-4209},

year  = {2024},

date = {2024-10-26},

urldate = {2024-10-26},

journal = {Medical Physics},

volume = {52},

issue = {1},

pages = {662–672},

abstract = {Background: Large reported variability in the material composition and geometrical components of the Xoft electronic high dose rate brachytherapy causes inter-source discrepancy in the source output. This variability is due to the manual manufacturing and assembly of the sources.



Purpose: This study aimed to develop a dosimetry software tool called E-Brachy to characterize the Xoft source and quantify the discrepancies in its photon spectrum and dosimetric properties.



Methods: E-Brachy is based on the Geant4 Monte Carlo toolkit and consists of two parts. In part one, the geometry and material composition for the source received in the computer-aided design format from the vendor were converted to the geometry description markup language format using the GUIMesh Python tool and integrated into the E-Brachy software. There was a large variation in material composition and thickness for some of the tube components. The simulation started from electrons and resulted in x-ray generations in the anode region. Multithreading, a track length estimation, and the uniform bremsstrahlung splitting variance reduction techniques were used to decrease the simulation time and increase the x-ray production. The photon energy, position, and momentum were saved into a phase space file as the photon exited the source, but before interacting with the external environment. The obtained x-ray energy spectrum was compared with measurements from the National Institute of Standards and Technology (NIST). In part two, by sampling from the generated photons, the dose rates and dosimetric parameters according to the TG-43 protocol were calculated for model S7500 and compared to the ones previously calculated for model S700 source, which were deemed identical by the manufacturer.



Results: The material composition that resulted in the most similar spectrum as the measured NIST spectrum with Pearson's correlation coefficient of 0.99 and a calculated Euclidean difference of 

0.061

±

0.001

 keV was chosen for further dosimetric analysis of the model S7500 source. Characteristic peaks showed the presence of tungsten, yttrium, and silver in the source components. Differences in dose rates between the two source models surpassed 20% for polar angles 

θ

≥

150

∘

 , reaching a peak at 

r

=

3

 cm and 

θ

=

175

∘

 . The differences in the radial dose function values were within 5%. The relative difference in percentage between the anisotropy function values of the two models was closer to 0 for smaller 

θ

 values, but at higher polar angles, they increased to 300%.



Conclusions: A software package called E-Brachy was successfully developed for the characterization and dosimetry of Xoft electronic brachytherapy sources. E-Brachy can be combined with spectral measurements to investigate the inter- and intra-source variability. The software package was tested by comparing the simulated spectra from the S7500 Xoft source model with NIST measurements and its TG-43 parameters with the S700 model. The TG-43 parameters between the two sources significantly exceed the recommendations of TG-56.



Keywords: dosimetry; electronic brachytherapy; monte carlo simulations.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Development of small, cost-efficient scintillating fiber detectors for automated synthesis of positron emission tomography radiopharmaceuticals},

author = {Hailey Ahn and Liam Carroll and Robert Hopewell and I-Huang Tsai and Dean Jolly and Gassan Massarweh and Shirin A Enger },

doi = {10.1002/mp.17369},

year  = {2024},

date = {2024-09-20},

urldate = {2024-09-20},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {169Yb-based high dose rate intensity modulated brachytherapy for focal treatment of prostate cancer},

author = {Maude Robitaille and Cynthia Ménard and Gabriel Famulari and Dominic Béliveau-Nadeau and Shirin A Enger},

doi = {10.1016/j.brachy.2024.05.005},

year  = {2024},

date = {2024-07-21},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Penalty weight tuning in high dose rate brachytherapy using multi-objective Bayesian optimization},

author = {Hossein Jafarzadeh and Majd Antaki and Ximeng Mao and Marie Duclos and Farhard Maleki and Shirin A Enger },

doi = {10.1088/1361-6560/ad4448},

year  = {2024},

date = {2024-05-21},

urldate = {2024-05-21},

journal = {Physics in Medicine & Biology},

volume = {69},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Investigation of dosimetric characteristics of radiochromic film in response to alpha particles emitted from Americium-241},

author = {Victor D Diaz-Martinez and Mélodie Cyr and Slobodan Devic and Nada Tomic and David F Lewis and Shirin A Enger },

doi = {10.1002/mp.17133},

year  = {2024},

date = {2024-05-20},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Characterizing the voxel-based approaches in radioembolization dosimetry with reDoseMC},

author = {Taehyung Peter Kim and Shirin A Enger},

doi = { 10.1002/mp.17054},

year  = {2024},

date = {2024-05-04},

urldate = {2024-05-04},

journal = {Medical Physics},

volume = {51},

number = {6},

pages = {4007-4027},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{quetin2024deep,

title = {Deep learning for high-resolution dose prediction in high dose rate brachytherapy for breast cancer treatment},

author = {Sébastien Quetin and Boris Bahoric and Farhad Maleki and Shirin A Enger},

doi = {10.1088/1361-6560/ad3dbd},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

journal = {Physics in Medicine & Biology},

volume = {69},

number = {10},

publisher = {IOP Publishing},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{busse2024aapm,

title = {AAPM medical physics practice guideline 14. a: Yttrium-90 microsphere radioembolization},

author = {Nathan C Busse and Muthana SAL Al-Ghazi and Nadine Abi-Jaoudeh and Diane Alvarez and Ahmet S Ayan and Erli Chen and Michael D Chuong and William A Dezarn and Shirin A Enger and Stephen A Graves and Robert F Hobbs and Mary Ellen Jafari and S Peter Kim and Nichole M Maughan and Andrew M Polemi and Jennifer R Stickel},

doi = {10.1159/000343878},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

journal = {Journal of applied clinical medical physics},

volume = {25},

number = {2},

pages = {e14157},

publisher = {Wiley Online Library},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{kalinowski2024rapidbrachytg43,

title = {RapidBrachyTG43: A Geant4-based TG-43 parameter and dose calculation module for brachytherapy dosimetry},

author = {Jonathan Kalinowski and Shirin A Enger},

doi = {10.1002/mp.16948},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

journal = {Medical Physics},

volume = {51},

number = {5},

pages = {3746–757},

publisher = {Wiley Online Library},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{rodrigues2024radiation,

title = {Radiation hardness of open Fabry-Pérot microcavities},

author = {Fernanda C Rodrigues-Machado and Erika Janitz and Simon Bernard and Hamed Bekerat and Malcolm McEwen and James Renaud and Shirin A Enger and Lilian Childress and Jack C Sankey},

doi = {10.1364/OE.522332},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

journal = {Optics Express},

volume = {32},

number = {10},

pages = {17189–17196},

publisher = {Optica Publishing Group},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{dumancic2024pioneering,

title = {Pioneering women in nuclear and radiation sciences},

author = {Mirta Dumancic and Shirin A Enger},

doi = {10.1016/j.radonc.2024.110374},

year  = {2024},

date = {2024-01-01},

urldate = {2024-01-01},

journal = {Radiotherapy and Oncology},

volume = {197},

pages = {110374},

publisher = {Elsevier},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey_50,

title = {Dosimetry of [18F]TRACK, the first PET tracer for imaging of TrkB/C receptors in humans},

author = {Alexander Thiel and Alexey Kostikov and Hailey Ahn and Youstina Daoud and Jean-Paul Soucy and Stephan Blinder and Carolin Jaworski and Carmen Wängler and Björn Wängler and Freimut Juengling and Shirin A. Enger and Ralf Schirrmacher },

doi = {10.1186/s41181-023-00219-x},

year  = {2023},

date = {2023-10-23},

urldate = {2023-10-23},

journal = {EJNMMI Radiopharm Chem},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {M-TAG: A modular teaching-aid for Geant4},

author = {Liam Carroll and Shirin A. Enger},

year  = {2023},

date = {2023-09-19},

urldate = {2023-09-19},

journal = {Heliyon},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {A MC-based anthropomorphic test case for commissioning model-based dose  calculation in interstitial breast 192-Ir HDR brachytherapy},

author = {V. Peppa and RM. Thomson and Shirin A. Enger and Fonseca GP and C. Lee and JNE Lucero and F. Mourtada, FA. Siebert, J. Vijande, P. Papagiannis},

year  = {2023},

date = {2023-07-07},

journal = {Medical Physics},

pages = {4675-4687},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Development of a hydrated electron dosimeter for radiotherapy applications: A proof of concept},

author = {Julien Mégrourèche and Hamed Bekerat and Jingyi Bian and Alaina Bui and Jack Sankey and Lilian Childress and Shirin A. Enger},

doi = {10.1002/mp.16555},

year  = {2023},

date = {2023-06-19},

urldate = {2023-06-19},

journal = {Medical Physics},

abstract = {Background: Hydrated electrons, which are short-lived products of radiolysis in water, increase the optical absorption of water, providing a pathway toward near-tissue-equivalent clinical radiation dosimeters. This has been demonstrated in high-dose-per-pulse radiochemistry research, but, owing to the weak absorption signal, its application in existing low-dose-per-pulse radiotherapy provided by clinical linear accelerators (linacs) has yet to be investigated.



Purpose: The aims of this study were to measure the optical absorption associated with hydrated electrons produced by clinical linacs and to assess the suitability of the technique for radiotherapy (⩽ 1 cGy per pulse) applications.



Methods: 40 mW of 660-nm laser light was sent five passes through deionized water contained in a 10 

×

4

×

 2 cm3 glass-walled cavity by using four broadband dielectric mirrors, two on each side of the cavity. The light was collected with a biased silicon photodetector. The water cavity was then irradiated by a Varian TrueBeam linac with both photon (10 MV FFF, 6 MV FFF, 6 MV) and electron beams (6 MeV) while monitoring the transmitted laser power for absorption transients. Radiochromic EBT3 film measurements were also performed for comparison.



Results: Examination of the absorbance profiles showed clear absorption changes in the water when radiation pulses were delivered. Both the amplitude and the decay time of the signal appeared consistent with the absorbed dose and the characteristics of the hydrated electrons. By using literature value for the hydrated electron radiation chemical yield (3.0±0.3), we inferred doses of 2.1±0.2 mGy (10 MV FFF), 1.3±0.1 mGy (6 MV FFF), 0.45±0.06 mGy (6 MV) for photons, and 0.47±0.05 mGy (6 MeV) for electrons, which differed from EBT3 film measurements by 0.6%, 0.8%, 10%, and 15.7%, respectively. The half-life of the hydrated electrons in the solution was ∼ 24 

μs.



Conclusions: By measuring 660-nm laser light transmitted through a cm-scale, multi-pass water cavity, we observed absorption transients consistent with hydrated electrons generated by clinical linac radiation. The agreement between our inferred dose and EBT3 film measurements suggests this proof-of-concept system represents a viable pathway toward tissue-equivalent dosimeters for clinical radiotherapy applications.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey_33,

title = {GEANT4-DNA simulation of temperature-dependent and pH-dependent yields of chemical radiolytic species},

author = {Jingyi Bian and Juan Duran and Wook-Geun Shin and Jose Ramos-Méndez and Jack C Sankey and Lilian Childress and Jan Seuntjens and Shirin A Enger

},

doi = {10.1088/1361-6560/acd90d},

year  = {2023},

date = {2023-06-15},

journal = {Physics in Medicine & Biology},

abstract = {Objective.GEANT4-DNA can simulate radiation chemical yield (G-value) for radiolytic species such as the hydrated electron (eaq-) with the independent reaction times (IRT) method, however, only at room temperature and neutral pH. This work aims to modify the GEANT4-DNA source code to enable the calculation ofG-values for radiolytic species at different temperatures and pH values.Approach.In the GEANT4-DNA source code, values of chemical parameters such as reaction rate constant, diffusion coefficient, Onsager radius, and water density were replaced by corresponding temperature-dependent polynomials. The initial concentration of hydrogen ion (H+)/hydronium ion (H3O+) was scaled for a desired pH using the relationship pH = -log10[H+]. To validate our modifications, two sets of simulations were performed. (A) A water cube with 1.0 km sides and a pH of 7 was irradiated with an isotropic electron source of 1 MeV. The end time was 1μs. The temperatures varied from 25 °C to 150 °C. (B) The same setup as (A) was used, however, the temperature was set to 25 °C while the pH varied from 5 to 9. The results were compared with published experimental and simulated work.Main results.The IRT method in GEANT4-DNA was successfully modified to simulateG-values for radiolytic species at different temperatures and pH values. Our temperature-dependent results agreed with experimental data within 0.64%-9.79%, and with simulated data within 3.52%-12.47%. The pH-dependent results agreed well with experimental data within 0.52% to 3.19% except at a pH of 5 (15.99%) and with simulated data within 4.40%-5.53%. The uncertainties were below ±0.20%. Overall our results agreed better with experimental than simulation data.Significance.Modifications in the GEANT4-DNA code enabled the calculation ofG-values for radiolytic species at different temperatures and pH values.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey_29,

title = {Fast DM,M calculation in LDR brachytherapy using deep learning methods},

author = {Francisco Berumen and Shirin A. Enger and Luc Beaulieu},

doi = {10.1088/1361-6560/accd42},

year  = {2023},

date = {2023-05-23},

urldate = {2023-05-23},

journal = {Physics in Medicine & Biology},

abstract = {Objective.The Monte Carlo (MC) method provides a complete solution to the tissue heterogeneity effects in low-energy low-dose rate (LDR) brachytherapy. However, long computation times limit the clinical implementation of MC-based treatment planning solutions. This work aims to apply deep learning (DL) methods, specifically a model trained with MC simulations, to predict accurate dose to medium in medium (DM,M) distributions in LDR prostate brachytherapy.Approach.To train the DL model, 2369 single-seed configurations, corresponding to 44 prostate patient plans, were used. These patients underwent LDR brachytherapy treatments in which125I SelectSeed sources were implanted. For each seed configuration, the patient geometry, the MC dose volume and the single-seed plan volume were used to train a 3D Unet convolutional neural network. Previous knowledge was included in the network as anr2kernel related to the first-order dose dependency in brachytherapy. MC and DL dose distributions were compared through the dose maps, isodose lines, and dose-volume histograms. Features enclosed in the model were visualized.Main results.Model features started from the symmetrical kernel and finalized with an anisotropic representation that considered the patient organs and their interfaces, the source position, and the low- and high-dose regions. For a full prostate patient, small differences were seen below the 20% isodose line. When comparing DL-based and MC-based calculations, the predicted CTVD90metric had an average difference of -0.1%. Average differences for OARs were -1.3%, 0.07%, and 4.9% for the rectumD2cc, the bladderD2cc, and the urethraD0.1cc. The model took 1.8 ms to predict a complete 3DDM,Mvolume (1.18 M voxels).Significance.The proposed DL model stands for a simple and fast engine which includes prior physics knowledge of the problem. Such an engine considers the anisotropy of a brachytherapy source and the patient tissue composition.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey_34,

title = {A MC-based anthropomorphic test case for commissioning model-based dose calculation in interstitial breast 192-Ir HDR brachytherapy},

author = {Vasiliki Peppa and Rowan M. Thomson and Shirin A. Enger and Gabriel P. Fonseca and Choonik Lee and Joseph N. E. Lucero and Firas Mourtada and Frank-André Siebert and Javier Vijande and Panagiotis Papagiannis},

doi = {10.1002/mp.16455},

year  = {2023},

date = {2023-05-17},

urldate = {2023-05-17},

journal = {Medical Physics},

abstract = {Purpose: To provide the first clinical test case for commissioning of 192 Ir brachytherapy model-based dose calculation algorithms (MBDCAs) according to the AAPM TG-186 report workflow.



Acquisition and validation methods: A computational patient phantom model was generated from a clinical multi-catheter 192 Ir HDR breast brachytherapy case. Regions of interest (ROIs) were contoured and digitized on the patient CT images and the model was written to a series of DICOM CT images using MATLAB. The model was imported into two commercial treatment planning systems (TPSs) currently incorporating an MBDCA. Identical treatment plans were prepared using a generic 192 Ir HDR source and the TG-43-based algorithm of each TPS. This was followed by dose to medium in medium calculations using the MBDCA option of each TPS. Monte Carlo (MC) simulation was performed in the model using three different codes and information parsed from the treatment plan exported in DICOM radiation therapy (RT) format. Results were found to agree within statistical uncertainty and the dataset with the lowest uncertainty was assigned as the reference MC dose distribution.



Data format and usage notes: The dataset is available online at http://irochouston.mdanderson.org/rpc/BrachySeeds/BrachySeeds/index.html,https://doi.org/10.52519/00005. Files include the treatment plan for each TPS in DICOM RT format, reference MC dose data in RT Dose format, as well as a guide for database users and all files necessary to repeat the MC simulations.



Potential applications: The dataset facilitates the commissioning of brachytherapy MBDCAs using TPS embedded tools and establishes a methodology for the development of future clinical test cases. It is also useful to non-MBDCA adopters for intercomparing MBDCAs and exploring their benefits and limitations, as well as to brachytherapy researchers in need of a dosimetric and/or a DICOM RT information parsing benchmark. Limitations include specificity in terms of radionuclide, source model, clinical scenario, and MBDCA version used for its preparation.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey_28,

title = {Applying the column generation method to the intensity modulated high dose rate brachytherapy inverse planning problem},

author = {Majd Antaki and Marc-André Renaud and Marc Morcos and Jan Seuntjens and Shirin A. Enger },

doi = {10.1088/1361-6560/acbc63},

year  = {2023},

date = {2023-03-13},

urldate = {2023-03-13},

journal = {Physics in Medicine & Biology},

abstract = {Objective.Intensity modulated high dose rate brachytherapy (IMBT) is a rapidly developing application of brachytherapy where anisotropic dose distributions can be produced at each source dwell position. This technique is made possible by placing rotating metallic shields inside brachytherapy needles or catheters. By dynamically directing the radiation towards the tumours and away from the healthy tissues, a more conformal dose distribution can be obtained. The resulting treatment planning involves optimizing dwell position and shield angle (DPSA). The aim of this study was to investigate the column generation method for IMBT treatment plan optimization.Approach.A column generation optimization algorithm was developed to optimize the dwell times and shield angles. A retrospective study was performed on 10 prostate cases using RapidBrachyMCTPS. At every iteration, the plan was optimized with the chosen DPSA which would best improve the cost function that was added to the plan. The optimization process was stopped when the remaining DPSAs would not add value to the plan to limit the plan complexity.Main results.The average number of DPSAs and voxels were 2270 and 7997, respectively. The column generation approach yielded near-optimal treatment plans by using only 11% of available DPSAs on average in ten prostate cases. The coverage and organs at risk constraints passed in all ten cases.Significance.The column generation method produced high-quality deliverable prostate IMBT plans. The treatment plan quality reached a plateau, where adding more DPSAs had a minimal effect on dose volume histogram parameters. The iterative nature of the column generation method allows early termination of the treatment plan creation process as soon as the dosimetric indices from dose volume histogram satisfy the clinical requirements or if their values stabilize.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey_27,

title = {Effects of incoming particle energy and cluster size on the G-value of hydrated electrons},

author = {Alaina Bui and Hamed Bekerat and Lilian Childress and Jack Sankey and Jan Seuntjens and Shirin A. Enger},

url = {https://doi.org/10.1016/j.ejmp.2023.102540},

doi = {10.1016/j.ejmp.2023.102540},

year  = {2023},

date = {2023-02-16},

urldate = {2023-02-16},

journal = {Physics in Medicine & Biology},

abstract = {In hydrated electron (e-aq) dosimetry, absorbed radiation dose to water is measured by monitoring the concentration of radiation-induced e-aq. However, to obtain accurate dose, the radiation chemical yield of e-aq, G(e-aq), is needed for the radiation quality/setup under investigation. The aim of this study was to investigate the time-evolution of the G-values for the main generated reactive species during water radiolysis using GEANT4-DNA. The effects of cluster size and linear energy transfer (LET) on G(e-aq) were examined. Validity of GEANT4-DNA for calculation of G(e-aq) for clinically relevant energies was studied. Three scenarios were investigated with different phantom sizes and incoming electron energies (1 keV to 1 MeV). The time evolution of G(e-aq) was in good agreement with published data and did not change with decreasing phantom size. The time-evolution of the G-values increases with increasing LET for all radiolytic species. The particle tracks formed with high-energy electrons are separated and the resulting reactive species develop independently in time. With decreasing energy, the mean separation distance between reactive species decreases. The particle tracks might not initially overlap but will overlap shortly thereafter due to diffusion of reactive species, increasing the probability of e-aq recombination with other species. This also explains the decrease of G(e-aq) with cluster size and LET. Finally, if all factors are kept constant, as the incoming electron energy increases to clinically relevant energies, G(e-aq) remains similar to its value at 1 MeV, hence GEANT4-DNA can be used for clinically relevant energies.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey_30,

title = {Dosimetric impact of a robust optimization approach to mitigate effects from rotational uncertainty in prostate intensity-modulated brachytherapy},

author = {Björn Morén and Majd Antaki and Gabriel Famulari and Marc Morcos and Torbjörn Larsson and Shirin A Enger and Åsa Carlsson Tedgren},

doi = {10.1002/mp.16134},

year  = {2022},

date = {2022-12-22},

journal = {Medical Physics},

abstract = {Background: Intensity-modulated brachytherapy (IMBT) is an emerging technology for cancer treatment, in which radiation sources are shielded to shape the dose distribution. The rotatable shields provide an additional degree of freedom, but also introduce an additional, directional, type of uncertainty, compared to conventional high-dose-rate brachytherapy (HDR BT).



Purpose: We propose and evaluate a robust optimization approach to mitigate the effects of rotational uncertainty in the shields with respect to planning criteria.



Methods: A previously suggested prototype for platinum-shielded prostate 169 Yb-based dynamic IMBT is considered. We study a retrospective patient data set (anatomical contours and catheter placement) from two clinics, consisting of six patients that had previously undergone conventional 192 Ir HDR BT treatment. The Monte Carlo-based treatment planning software RapidBrachyMCTPS is used for dose calculations. In our computational experiments, we investigate systematic rotational shield errors of ±10° and ±20°, and the same systematic error is applied to all dwell positions in each scenario. This gives us three scenarios, one nominal and two with errors. The robust optimization approach finds a compromise between the average and worst-case scenario outcomes.



Results: We compare dose plans obtained from standard models and their robust counterparts. With dwell times obtained from a linear penalty model (LPM), for 10° errors, the dose to urethra (D0.1cc) and rectum (D0.1cc and D1cc) increase with up to 5% and 7%, respectively, in the worst-case scenario, while with the robust counterpart, the corresponding increases were 3% and 3%. For all patients and all evaluated criteria, the worst-case scenario outcome with the robust approach had lower deviation compared to the standard model, without compromising target coverage. We also evaluated shield errors up to 20° and while the deviations increased to a large extent with the standard models, the robust models were capable of handling even such large errors.



Conclusions: We conclude that robust optimization can be used to mitigate the effects from rotational uncertainty and to ensure the treatment plan quality of IMBT.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Simulation of a novel, non-invasive radiation detector to measure the arterial input function for dynamic PET},

author = {Liam Carroll and Shirin A. Enger},

url = {https://doi-org.proxy3.library.mcgill.ca/10.1002/mp.16055



},

doi = {10.1002/mp.16055},

year  = {2022},

date = {2022-10-17},

urldate = {2022-10-17},

journal = {Medical Physics },

abstract = {Background:

Dynamic positron emission tomography (dPET) is a nuclear medicine imaging technique providing functional images for organs of interest with applications in oncology, cardiology, and drug discovery. This technique requires the acquisition of the time-course arterial plasma activity concentration, called the arterial input function (AIF), which is conventionally acquired via arterial blood sampling.



Purpose:

The aim of this study was to A) optimize the geometry for a novel and cost efficient non-invasive detector called NID designed to measure the AIF for dPET scans through Monte Carlo simulations and B) develop a clinical data analysis chain to successfully separate the arterial component of a simulated AIF signal from the venous component.



Methods:

The NID was optimized by using an in-house Geant4-based software package. The sensitive volume of the NID consists of a band of 10 cm long and 1 mm in diameter scintillating fibers placed over a wrist phantom. The phantom was simulated as a cylinder, 10 cm long and 6.413 cm in diameter comprised of polyethylene with two holes placed through it to simulate the patient's radial artery and vein. This phantom design was chosen to match the wrist phantom used in our previous proof of concept work. Two geometries were simulated with different arrangements of scintillating fibers. The first design used a single layer of 64 fibers. The second used two layers, an inner layer with 29 fibers and an outer layer with 30 fibers. Four positron emitting radioisotopes were simulated: 18F, 11C, 15O and 68Ga with 100 million simulated decay events per run. The total and intrinsic efficiencies of both designs were calculated as well as the full width half max (FWHM) of the signal. In addition, contribution by the annihilation photons vs positrons to the signal was investigated. The results obtained from the two simulated detector models were compared. A clinical data analysis chain using an expectation maximization maximum likelihood algorithm was tested. This analysis chain will be used to separate arterial counts from the total signal.



Results:

The second NID design with two layers of scintillating fibers had a higher efficiency for all simulations with a maximum increase of 17% total efficiency for 11C simulation. All simulations had a significant annihilation photon contribution. The signal for 18F and 11C was almost entirely due to photons. The clinical data analysis chain was within 1% of the true value for 434 out of 440 trials. Further experimental studies to validate these simulations will be required.



Conclusions:

The design of the NID was optimized and its efficiency increased through Monte Carlo simulations. A clinical data analysis chain was successfully developed to separate the arterial component of an AIF signal from the venous component. The simulations show that the NID can be used to accurately measure the AIF non-invasively for dPET scans.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Simulation of a novel, non-invasive radiation detector to measure the arterial input function for dynamic positron emission tomography},

author = {Liam Carroll and Shirin A Enger },

doi = {10.1002/mp.16055},

year  = {2022},

date = {2022-10-17},

keywords = {},

pubstate = {published},

tppubtype = {article}

}