@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 = {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 = {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{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}

}