Publications

@article{morcos_impact_2021,

title = {On the impact of absorbed dose specification, tissue heterogeneities, and applicator heterogeneities on Monte Carlo-based dosimetry of Ir-192, Se-75, and Yb-169 in conventional and intensity-modulated brachytherapy for the treatment of cervical cancer},

author = {Marc Morcos and Akila N. Viswanathan and Shirin A. Enger},

doi = {10.1002/mp.14802},

issn = {2473-4209},

year  = {2021},

date = {2021-05-01},

journal = {Medical Physics},

volume = {48},

number = {5},

pages = {2604--2613},

abstract = {PURPOSE: The purpose of this study was to evaluate the impact of dose reporting schemes and tissue/applicator heterogeneities for 192 Ir-, 75 Se-, and 169 Yb-based MRI-guided conventional and intensity-modulated brachytherapy. METHODS AND MATERIALS: Treatment plans using a variety of dose reporting and tissue/applicator segmentation schemes were generated for a cohort (n = 10) of cervical cancer patients treated with 192 Ir-based Venezia brachytherapy. Dose calculations were performed using RapidBrachyMCTPS, a Geant4-based research Monte Carlo treatment planning system. Ultimately, five dose calculation scenarios were evaluated: (a) dose to water in water (Dw,w ); (b) Dw,w taking the applicator material into consideration (Dw,wApp ); (c) dose to water in medium (Dw,m ); (d and e) dose to medium in medium with mass densities assigned either nominally per structure (Dm,m (Nom) ) or voxel-by-voxel (Dm,m ). 

RESULTS: Ignoring the plastic Venezia applicator (Dw,wApp ) overestimates Dm,m by up to 1% (average) with high energy source (192 Ir and 75 Se) and up to 2% with 169 Yb. Scoring dose to water (Dw,wApp or Dw,m ) generally overestimates dose and this effect increases with decreasing photon energy. Reporting dose other than Dm,m (or Dm,m Nom ) for 169 Yb-based conventional and intensity-modulated brachytherapy leads to a simultaneous overestimation (up to 4%) of CTVHR D90 and underestimation (up to 2%) of bladder D2cc due to a significant dip in the mass-energy absorption ratios at the depths of nearby targets and OARs. Using a nominal mass-density assignment per structure, rather than a CT-derived voxel-by-voxel assignment for MRI-guided brachytherapy, amounts to a dose error up to 1% for all radionuclides considered. 

CONCLUSIONS: The effects of the considered dose reporting schemes trend correspondingly between conventional and intensity-modulated brachytherapy. In the absence of CT-derived mass densities, MRI-only-based dosimetry can adequately approximate Dm,m by assigning nominal mass densities to structures. Tissue and applicator heterogeneities do not significantly impact dosimetry for 192 Ir and 75 Se, but do for 169 Yb; dose reporting must be explicitly defined since Dw,m and Dw,w may overstate the dosimetric benefits.},

keywords = {Brachytherapy, Computer-Assisted, dynamic shield brachytherapy, Female, Humans, IMBT, Intensity modulated brachytherapy, Iridium Radioisotopes, Monte Carlo Method, MR-guided brachytherapy, Radiotherapy Dosage, Radiotherapy Planning, rotating shield brachytherapy, RSBT, Uterine Cervical Neoplasms},

pubstate = {published},

tppubtype = {article}

}

@article{morcos_novel_2021,

title = {A novel minimally invasive dynamic-shield, intensity-modulated brachytherapy system for the treatment of cervical cancer},

author = {Marc Morcos and Majd Antaki and Akila N. Viswanathan and Shirin A. Enger},

doi = {10.1002/mp.14459},

issn = {2473-4209},

year  = {2021},

date = {2021-01-01},

journal = {Medical Physics},

volume = {48},

number = {1},

pages = {71--79},

abstract = {PURPOSE: To present a novel, MRI-compatible dynamicshield intensity modulated brachytherapy (IMBT) applicator and delivery system using 192 Ir, 75 Se, and 169 Yb radioisotopes for the treatment of locally advanced cervical cancer. Needle-free IMBT is a promising technique for improving target coverage and organs at risk (OAR) sparing. 

METHODS AND MATERIALS: The IMBT delivery system dynamically controls the rotation of a novel tungsten shield placed inside an MRI-compatible, 6-mm wide intrauterine tandem. Using 36 cervical cancer cases, conventional intracavitary brachytherapy (IC-BT) and intracavitary/interstitial brachytherapy (IC/IS-BT) (10Ci 192 Ir) plans were compared to IMBT (10Ci 192 Ir; 11.5Ci 75 Se; 44Ci 169 Yb). All plans were generated using the Geant4-based Monte Carlo dose calculation engine, RapidBrachyMC. Treatment plans were optimized then normalized to the same high-risk clinical target volume (HR-CTV) D90 and the D2cc for bladder, rectum, and sigmoid in the research brachytherapy planning system, RapidBrachyMCTPS. Plans were renormalized until either of the three OAR reached dose limits to calculate the maximum achievable HR-CTV D90 and D98 . RESULTS: Compared to IC-BT, IMBT with either of the three radionuclides significantly improves the HR-CTV D90 and D98 by up to 5.2% ± 0.3% (P textless 0.001) and 6.7% ± 0.5% (P textless 0.001), respectively, with the largest dosimetric enhancement when using 169 Yb followed by 75 Se and then 192 Ir. Similarly, D2cc for all OAR improved with IMBT by up to 7.7% ± 0.6% (P textless 0.001). For IC/IS-BT cases, needle-free IMBT achieved clinically acceptable plans with 169 Yb-based IMBT further improving HR-CTV D98 by 1.5% ± 0.2% (P = 0.034) and decreasing sigmoid D2cc by 1.9% ± 0.4% (P = 0.048). Delivery times for IMBT are increased by a factor of 1.7, 3.3, and 2.3 for 192 Ir, 75 Se, and 169 Yb, respectively, relative to conventional 192 Ir BT. 

CONCLUSIONS: Dynamic shield IMBT provides a promising alternative to conventional IC- and IC/IS-BT techniques with significant dosimetric enhancements and even greater improvements with intermediate energy radionuclides. The ability to deliver a highly conformal, OAR-sparing dose without IS needles provides a simplified method for improving the therapeutic ratio less invasively and in a less resource intensive manner.},

keywords = {Brachytherapy, Computer-Assisted, Female, Humans, Image-guided cervix brachytherapy, Intensity modulated brachytherapy, Monte Carlo based dosimetry, Monte Carlo Method, MRI-guided GYN brachytherapy, Organs at Risk, Radiotherapy Dosage, Radiotherapy Planning, Uterine Cervical Neoplasms},

pubstate = {published},

tppubtype = {article}

}

@article{antaki_fast_2020,

title = {Fast mixed integer optimization (FMIO) for high dose rate brachytherapy},

author = {Majd Antaki and Christopher L Deufel and Shirin A. Enger},

doi = {10.1088/1361-6560/aba317},

issn = {1361-6560},

year  = {2020},

date = {2020-12-01},

journal = {Physics in Medicine and Biology},

volume = {65},

number = {21},

pages = {215005},

abstract = {The purpose of this work was to develop an efficient quadratic mixed integer programming algorithm for high dose rate (HDR) brachytherapy treatment planning problems and integrate the algorithm into an open-source Monte Carlo based treatment planning software, RapidBrachyMCTPS. The mixed-integer algorithm yields a globally optimum solution to the dose volume histogram (DVH) based problem and, unlike other methods, is not susceptible to local minimum trapping. A hybrid linear-quadratic penalty model coupled to a mixed integer programming model was used to optimize treatment plans for 10 prostate cancer patients. Dose distributions for each dwell position were calculated with RapidBrachyMCTPS with type A uncertainties less than 0.2% in voxels within the planning target volume (PTV). The optimization process was divided into two parts. First, the data was preprocessed, in which the problem size was reduced by eliminating voxels that had negligible impact on the solution (e.g. far from the dwell position). Second, the best combination of dwell times to obtain a plan with the highest score was found. The dwell positions and dose volume constraints were used as input to a commercial mixed integer optimizer (Gurobi Optimization, Inc.). A penalty-based criterion was adopted for the scoring. The voxel-reduction technique successfully reduced the problem size by an average of 91%, without loss of quality. The preprocessing of the optimization process required on average 4 s and solving for the global maximum required on average 33 s. The total optimization time averaged 37 s, which is a substantial improvement over the ∼15 min optimization time reported in published literature. The plan quality was evaluated by evaluating dose volume metrics, including PTV D90, rectum and bladder D1cc and urethra D0.1cc. In conclusion, fast mixed integer optimization is an order of magnitude faster than current mixed-integer approaches for solving HDR brachytherapy treatment planning problems with DVH based metrics.},

keywords = {Algorithms, Brachytherapy, Computer-Assisted, Humans, Linear Models, Male, Monte Carlo Method, Prostatic Neoplasms, Radiation Dosage, Radiotherapy Dosage, Radiotherapy Planning, Software, Time Factors},

pubstate = {published},

tppubtype = {article}

}

@article{mao_rapidbrachydl_2020,

title = {RapidBrachyDL: Rapid Radiation Dose Calculations in Brachytherapy Via Deep Learning},

author = {Ximeng Mao and Joelle Pineau and Roy Keyes and Shirin A. Enger},

doi = {10.1016/j.ijrobp.2020.04.045},

issn = {1879-355X},

year  = {2020},

date = {2020-11-01},

journal = {International Journal of Radiation Oncology, Biology, Physics},

volume = {108},

number = {3},

pages = {802--812},

abstract = {PURPOSE: Detailed and accurate absorbed dose calculations from radiation interactions with the human body can be obtained with the Monte Carlo (MC) method. However, the MC method can be slow for use in the time-sensitive clinical workflow. The aim of this study was to provide a solution to the accuracy-time trade-off for 192Ir-based high-dose-rate brachytherapy by using deep learning. 

METHODS AND MATERIALS: RapidBrachyDL, a 3-dimensional deep convolutional neural network (CNN) model, is proposed to predict dose distributions calculated with the MC method given a patient's computed tomography images, contours of clinical target volume (CTV) and organs at risk, and treatment plan. Sixty-one patients with prostate cancer and 10 patients with cervical cancer were included in this study, with data from 47 patients with prostate cancer being used to train the model. 

RESULTS: Compared with ground truth MC simulations, the predicted dose distributions by RapidBrachyDL showed a consistent shape in the dose-volume histograms (DVHs); comparable DVH dosimetric indices including 0.73% difference for prostate CTV D90, 1.1% for rectum D2cc, 1.45% for urethra D0.1cc, and 1.05% for bladder D2cc; and substantially smaller prediction time, acceleration by a factor of 300. RapidBrachyDL also demonstrated good generalization to cervical data with 1.73%, 2.46%, 1.68%, and 1.74% difference for CTV D90, rectum D2cc, sigmoid D2cc, and bladder D2cc, respectively, which was unseen during the training. 

CONCLUSION: Deep CNN-based dose estimation is a promising method for patient-specific brachytherapy dosimetry. Desired radiation quantities can be obtained with accuracies arbitrarily close to those of the source MC algorithm, but with much faster computation times. The idea behind deep CNN-based dose estimation can be safely extended to other radiation sources and tumor sites by following a similar training process.},

keywords = {Brachytherapy, Colon, Computer, Computer-Assisted, Deep Learning, Female, Humans, Iridium Radioisotopes, Male, Monte Carlo Method, Neural Networks, Organs at Risk, Prostate, Prostatic Neoplasms, Radiotherapy Dosage, Radiotherapy Planning, Rectum, Retrospective Studies, Sigmoid, Urinary Bladder, Uterine Cervical Neoplasms},

pubstate = {published},

tppubtype = {article}

}

@article{famulari_can_2020,

title = {Can intermediate-energy sources lead to elevated bone doses for prostate and head & neck high-dose-rate brachytherapy?},

author = {Gabriel Famulari and Joanne Alfieri and Marie Duclos and Té Vuong and Shirin A. Enger},

doi = {10.1016/j.brachy.2019.12.004},

issn = {1873-1449},

year  = {2020},

date = {2020-04-01},

journal = {Brachytherapy},

volume = {19},

number = {2},

pages = {255--263},

abstract = {PURPOSE: Several radionuclides with high (60Co, 75Se) and intermediate (169Yb, 153Gd) energies have been investigated as alternatives to 192Ir for high-dose-rate brachytherapy. The purpose of this study was to evaluate the impact of tissue heterogeneities for these five high- to intermediate-energy sources in prostate and head & neck brachytherapy. METHODS AND MATERIALS: Treatment plans were generated for a cohort of prostate (n = 10) and oral tongue (n = 10) patients. Dose calculations were performed using RapidBrachyMCTPS, an in-house Geant4-based Monte Carlo treatment planning system. Treatment plans were simulated using 60Co, 192Ir, 75Se, 169Yb, and 153Gd as the active core of the microSelectron v2 source. Two dose calculation scenarios were presented: (1) dose to water in water (Dw,w), and (2) dose to medium in medium (Dm,m). 

RESULTS: Dw,w overestimates planning target volume coverage compared with Dm,m, regardless of photon energy. The average planning target volume D90 reduction was ∼1% for high-energy sources, whereas larger differences were observed for intermediate-energy sources (1%-2% for prostate and 4%-7% for oral tongue). Dose differences were not clinically relevant (textless5%) for soft tissues in general. Going from Dw,w to Dm,m, bone doses were increased two- to three-fold for 169Yb and four- to five-fold for 153Gd, whereas the ratio was close to ∼1 for high-energy sources. 

CONCLUSIONS: Dw,w underestimates the dose to bones and, to a lesser extent, overestimates the dose to soft tissues for radionuclides with average energies lower than 192Ir. Further studies regarding bone toxicities are needed before intermediate-energy sources can be adopted in cases where bones are in close vicinity to the tumor.},

keywords = {Bone and Bones, Brachytherapy, Cobalt Radioisotopes, Computer Simulation, Computer-Assisted, Dose calculation, Gadolinium, Humans, Intermediate-energy source, Iridium Radioisotopes, Male, Monte Carlo, Prostatic Neoplasms, Radiation Dosage, Radioisotopes, Radiotherapy Dosage, Radiotherapy Planning, Selenium Radioisotopes, Tissue composition, Tongue Neoplasms, Ytterbium},

pubstate = {published},

tppubtype = {article}

}

@article{famulari_novel_2020,

title = {A novel 169 Yb-based dynamic-shield intensity modulated brachytherapy delivery system for prostate cancer},

author = {Gabriel Famulari and Marie Duclos and Shirin A. Enger},

doi = {10.1002/mp.13959},

issn = {2473-4209},

year  = {2020},

date = {2020-03-01},

journal = {Medical Physics},

volume = {47},

number = {3},

pages = {859--868},

abstract = {PURPOSE: Intensity modulated brachytherapy (IMBT) is a novel high dose rate brachytherapy (HDR BT) technique which incorporates static or dynamic shielding to increase tumor coverage and/or spare healthy tissues. The purpose of this study is to present a novel delivery system (AIM-Brachy) design that can enable dynamic-shield IMBT for prostate cancer. 

METHODS: The AIM-Brachy system dynamically controls the rotation of platinum shields, placed within interstitial catheters, which partially collimate the radiation emitted from an 169 Yb source. Conventional HDR BT (10 Ci 192 Ir) and IMBT (18 Ci 169 Yb) plans were generated for 12 patients using an in-house column generation-based optimizer, coupled to a Geant4-based dose calculation engine, RapidBrachyMC. Treatment plans were normalized to match the same PTV D90 coverage as the clinical plan. Intershield attenuation effects were taken into account. A sensitivity analysis was performed to evaluate the dosimetric impact of systematic longitudinal source positioning errors ( ± 1 mm, ± 2 mm, and ± 3 mm) and rotational errors ( ± 5 ∘ , ± 10 ∘ , and ± 15 ∘ ) on clinically relevant parameters (PTV D90 and urethra D10 ). 

RESULTS: The platinum shield reduced the dose rate on the shielded side at 1 cm to 18.1% of the dose rate on the unshielded side. For equal PTV D90 coverage, the urethral D10 was reduced by 13.3% ± 4.7%, without change to other plan quality indices (PTV V100 , V150, V200 , bladder V75 , rectum V75 , HI, COIN). Delivery times for HDR BT and IMBT were 9.2 ± 1.6 min and 18.6 ± 4.0 min, respectively. In general, the PTV D90 was more sensitive to source positioning errors than rotational errors, while the urethral D10 was more sensitive to rotational errors than source positioning errors. For a typical range of positioning errors ( ± 1 mm, ± 5 ∘ ), the overall tolerance was textless2%. 

CONCLUSIONS: The AIM-Brachy system was proposed to deliver dynamic-shield IMBT for prostate cancer with the potential to create a low dose tunnel within the urethra. The urethra-sparing properties are desirable to minimize the occurrence and severity of urethral strictures or, alternatively, to provide a method for dose escalation.},

keywords = {Brachytherapy, Cohort Studies, Computer-Assisted, Humans, IMBT, Intensity-Modulated, Male, Monte Carlo, Monte Carlo Method, prostate cancer, Prostatic Neoplasms, Radioisotopes, Radiotherapy, Radiotherapy Planning, Uncertainty, Yb-169, Ytterbium},

pubstate = {published},

tppubtype = {article}

}

@article{enger_model-based_2020,

title = {Model-Based Dose Calculation Algorithms for Brachytherapy Dosimetry},

author = {Shirin A. Enger and Javier Vijande and Mark J. Rivard},

doi = {10.1016/j.semradonc.2019.08.006},

issn = {1532-9461},

year  = {2020},

date = {2020-01-01},

journal = {Seminars in Radiation Oncology},

volume = {30},

number = {1},

pages = {77--86},

abstract = {The purpose of this study was to review the limitations of dose calculation formalisms for photon-emitting brachytherapy sources based on the American Association of Physicists in Medicine (AAPM) Task Group No. 43 (TG-43) report and to provide recommendations to transition to model-based dose calculation algorithms. Additionally, an overview of these algorithms and approaches is presented. The influence of tissue and seed/applicator heterogeneities on brachytherapy dose distributions for breast, gynecologic, head and neck, rectum, and prostate cancers as well as eye plaques and electronic brachytherapy treatments were investigated by comparing dose calculations based on the TG-43 formalism and model-based dose calculation algorithms.},

keywords = {Algorithms, Brachytherapy, Computer-Assisted, Female, Humans, Male, Medical, Models, Neoplasms, Photons, Practice Guidelines as Topic, Radiometry, Radiotherapy Dosage, Radiotherapy Planning, Societies, Theoretical},

pubstate = {published},

tppubtype = {article}

}

@article{kim_guide_2019,

title = {A guide to 90Y radioembolization and its dosimetry},

author = {S. Peter Kim and Claire Cohalan and Neil Kopek and Shirin A. Enger},

doi = {10.1016/j.ejmp.2019.09.236},

issn = {1724-191X},

year  = {2019},

date = {2019-12-01},

journal = {Physica medica: PM: an international journal devoted to the applications of physics to medicine and biology: official journal of the Italian Association of Biomedical Physics (AIFB)},

volume = {68},

pages = {132--145},

abstract = {Radioembolization gains continuous traction as a primarily palliative radiation treatment for hepatic tumours. A form of nuclear medicine therapy, Yttrium-90 containing microspheres are catheter guided and injected into the right, left, or a specifically selected hepatic artery. A multitude of comprehensive planning steps exist to ensure a thorough and successful treatment. Clear clinical and physiological guidelines have been established and nuclear imaging is used to plan and verify dose distributions. Radioembolization's treatment rationale is based on tumour and blood vessel dynamics that allow a targeted treatment approach. However, radioembolization's dosimetry is grossly oversimplified. In fact, the currently utilized clinical dosimetric standards (e.g. partition method) have persisted since the 1990s. Moreover, the multitude of radioembolization's intertwining components lies disjointed within the literature. Particularly relevant to new readers, this review provides a methodical guide that presents the treatment rationale behind every clinical step. The emerging dosimetry methods and its factors are further discussed to provide a comprehensive review on an essential research direction.},

keywords = {(90)Y, Clinical Background, Computer-Assisted, Dosimetry, Embolization, Humans, Radioembolization, Radiometry, Radiotherapy Planning, Therapeutic, Yttrium Radioisotopes},

pubstate = {published},

tppubtype = {article}

}

@article{song_commentary_2019,

title = {Commentary on Systematic Review of Intensity Modulated Brachytherapy (IMBT): Static and Dynamic Techniques},

author = {William Y. Song and Shirin A. Enger},

doi = {10.1016/j.ijrobp.2019.07.050},

issn = {1879-355X},

year  = {2019},

date = {2019-11-01},

journal = {International Journal of Radiation Oncology, Biology, Physics},

volume = {105},

number = {3},

pages = {493--494},

keywords = {Brachytherapy, Computer-Assisted, Radiotherapy Dosage, Radiotherapy Planning},

pubstate = {published},

tppubtype = {article}

}

@article{famulari_rapidbrachymctps_2018,

title = {RapidBrachyMCTPS: a Monte Carlo-based treatment planning system for brachytherapy applications},

author = {Gabriel Famulari and Marc-André Renaud and Christopher M. Poole and Michael D. C. Evans and Jan Seuntjens and Shirin A. Enger},

doi = {10.1088/1361-6560/aad97a},

issn = {1361-6560},

year  = {2018},

date = {2018-08-01},

journal = {Physics in Medicine and Biology},

volume = {63},

number = {17},

pages = {175007},

abstract = {Despite being considered the gold standard for brachytherapy dosimetry, Monte Carlo (MC) has yet to be implemented into a software for brachytherapy treatment planning. The purpose of this work is to present RapidBrachyMCTPS, a novel treatment planning system (TPS) for brachytherapy applications equipped with a graphical user interface (GUI), optimization tools and a Geant4-based MC dose calculation engine, RapidBrachyMC. Brachytherapy sources and applicators were implemented in RapidBrachyMC and made available to the user via a source and applicator library in the GUI. To benchmark RapidBrachyMC, TG-43 parameters were calculated for the microSelectron v2 (192Ir) and SelectSeed (125I) source models and were compared against previously validated MC brachytherapy codes. The performance of RapidBrachyMC was evaluated for a prostate high dose rate case. To assess the accuracy of RapidBrachyMC in a heterogeneous setup, dose distributions with a cylindrical shielded/unshielded applicator were validated against film measurements in a Solid WaterTM phantom. TG-43 parameters calculated using RapidBrachyMC generally agreed within 1%-2% of the results obtained in previously published work. For the prostate case, clinical dosimetric indices showed general agreement with Oncentra TPS within 1%. Simulation times were on the order of minutes on a single core to achieve uncertainties below 2% in voxels within the prostate. The calculation time was decreased further using the multithreading features of Geant4. In the comparison between MC-calculated and film-measured dose distributions, at least 95% of points passed the 3%/3 mm gamma index criteria in all but one case. RapidBrachyMCTPS can be used as a post-implant dosimetry toolkit, as well as for MC-based brachytherapy treatment planning. This software is especially well suited for the development of new source and applicator models.},

keywords = {Brachytherapy, Computer-Assisted, Humans, Imaging, Monte Carlo Method, Phantoms, Radiotherapy Dosage, Radiotherapy Planning, Software},

pubstate = {published},

tppubtype = {article}

}

@article{poole_determination_2015,

title = {Determination of subcellular compartment sizes for estimating dose variations in radiotherapy},

author = {Christopher M. Poole and Anders Ahnesjö and Shirin A. Enger},

doi = {10.1093/rpd/ncv305},

issn = {1742-3406},

year  = {2015},

date = {2015-09-01},

journal = {Radiation Protection Dosimetry},

volume = {166},

number = {1-4},

pages = {361--364},

abstract = {The variation in specific energy absorbed to different cell compartments caused by variations in size and chemical composition is poorly investigated in radiotherapy. The aim of this study was to develop an algorithm to derive cell and cell nuclei size distributions from 2D histology samples, and build 3D cellular geometries to provide Monte Carlo (MC)-based dose calculation engines with a morphologically relevant input geometry. Stained and unstained regions of the histology samples are segmented using a Gaussian mixture model, and individual cell nuclei are identified via thresholding. Delaunay triangulation is applied to determine the distribution of distances between the centroids of nearest neighbour cells. A pouring simulation is used to build a 3D virtual tissue sample, with cell radii randomised according to the cell size distribution determined from the histology samples. A slice with the same thickness as the histology sample is cut through the 3D data and characterised in the same way as the measured histology. The comparison between this virtual slice and the measured histology is used to adjust the initial cell size distribution into the pouring simulation. This iterative approach of a pouring simulation with adjustments guided by comparison is continued until an input cell size distribution is found that yields a distribution in the sliced geometry that agrees with the measured histology samples. The thus obtained morphologically realistic 3D cellular geometry can be used as input to MC-based dose calculation programs for studies of dose response due to variations in morphology and size of tumour/healthy tissue cells/nuclei, and extracellular material.},

keywords = {Algorithms, Breast Neoplasms, Cell Nucleus, Computer Simulation, Computer-Assisted, ErbB-2, Female, Humans, Image Processing, Imaging, Immunoenzyme Techniques, Male, Monte Carlo Method, Prostatic Neoplasms, Radiotherapy Dosage, Radiotherapy Planning, Receptor, Signal Processing, Subcellular Fractions, Three-Dimensional},

pubstate = {published},

tppubtype = {article}

}

@article{adams_interstitial_2014,

title = {Interstitial rotating shield brachytherapy for prostate cancer},

author = {Quentin E. Adams and Jinghzu Xu and Elizabeth K. Breitbach and Xing Li and Shirin A. Enger and William R. Rockey and Yusung Kim and Xiaodong Wu and Ryan T. Flynn},

doi = {10.1118/1.4870441},

issn = {2473-4209},

year  = {2014},

date = {2014-05-01},

journal = {Medical Physics},

volume = {41},

number = {5},

pages = {051703},

abstract = {PURPOSE: To present a novel needle, catheter, and radiation source system for interstitial rotating shield brachytherapy (I-RSBT) of the prostate. I-RSBT is a promising technique for reducing urethra, rectum, and bladder dose relative to conventional interstitial high-dose-rate brachytherapy (HDR-BT). 

METHODS: A wire-mounted 62 GBq(153)Gd source is proposed with an encapsulated diameter of 0.59 mm, active diameter of 0.44 mm, and active length of 10 mm. A concept model I-RSBT needle/catheter pair was constructed using concentric 50 and 75 μm thick nickel-titanium alloy (nitinol) tubes. The needle is 16-gauge (1.651 mm) in outer diameter and the catheter contains a 535 μm thick platinum shield. I-RSBT and conventional HDR-BT treatment plans for a prostate cancer patient were generated based on Monte Carlo dose calculations. In order to minimize urethral dose, urethral dose gradient volumes within 0-5 mm of the urethra surface were allowed to receive doses less than the prescribed dose of 100%. 

RESULTS: The platinum shield reduced the dose rate on the shielded side of the source at 1 cm off-axis to 6.4% of the dose rate on the unshielded side. For the case considered, for the same minimum dose to the hottest 98% of the clinical target volume (D(98%)), I-RSBT reduced urethral D(0.1cc) below that of conventional HDR-BT by 29%, 33%, 38%, and 44% for urethral dose gradient volumes within 0, 1, 3, and 5 mm of the urethra surface, respectively. Percentages are expressed relative to the prescription dose of 100%. For the case considered, for the same urethral dose gradient volumes, rectum D(1cc) was reduced by 7%, 6%, 6%, and 6%, respectively, and bladder D(1cc) was reduced by 4%, 5%, 5%, and 6%, respectively. Treatment time to deliver 20 Gy with I-RSBT was 154 min with ten 62 GBq (153)Gd sources. 

CONCLUSIONS: For the case considered, the proposed(153)Gd-based I-RSBT system has the potential to lower the urethral dose relative to HDR-BT by 29%-44% if the clinician allows a urethral dose gradient volume of 0-5 mm around the urethra to receive a dose below the prescription. A multisource approach is necessary in order to deliver the proposed (153)Gd-based I-RSBT technique in reasonable treatment times.},

keywords = {Brachytherapy, Catheters, Computer-Assisted, Equipment Design, Gadolinium, Humans, Iridium Radioisotopes, Male, Monte Carlo Method, Needles, Nickel, Platinum Compounds, Prostatic Neoplasms, Radiation Protection, Radioisotopes, Radiotherapy Dosage, Radiotherapy Planning, Rectum, Time Factors, Titanium, Urethra, Urinary Bladder},

pubstate = {published},

tppubtype = {article}

}

@article{enger_layered_2012,

title = {Layered mass geometry: a novel technique to overlay seeds and applicators onto patient geometry in Geant4 brachytherapy simulations},

author = {Shirin A. Enger and Guillaume Landry and Michel D'Amours and Frank Verhaegen and Luc Beaulieu and Makoto Asai and Joseph Perl},

doi = {10.1088/0031-9155/57/19/6269},

issn = {1361-6560},

year  = {2012},

date = {2012-10-01},

journal = {Physics in Medicine and Biology},

volume = {57},

number = {19},

pages = {6269--6277},

abstract = {A problem faced by all Monte Carlo (MC) particle transport codes is how to handle overlapping geometries. The Geant4 MC toolkit allows the user to create parallel geometries within a single application. In Geant4 the standard mass-containing geometry is defined in a simulation volume called the World Volume. Separate parallel geometries can be defined in parallel worlds, that is, alternate three dimensional simulation volumes that share the same coordinate system with the World Volume for geometrical event biasing, scoring of radiation interactions, and/or the creation of hits in detailed readout structures. Until recently, only one of those worlds could contain mass so these parallel worlds provided no solution to simplify a complex geometric overlay issue in brachytherapy, namely the overlap of radiation sources and applicators with a CT based patient geometry. The standard method to handle seed and applicator overlay in MC requires removing CT voxels whose boundaries would intersect sources, placing the sources into the resulting void and then backfilling the remaining space of the void with a relevant material. The backfilling process may degrade the accuracy of patient representation, and the geometrical complexity of the technique precludes using fast and memory-efficient coding techniques that have been developed for regular voxel geometries. The patient must be represented by the less memory and CPU-efficient Geant4 voxel placement technique, G4PVPlacement, rather than the more efficient G4NestedParameterization (G4NestedParam). We introduce for the first time a Geant4 feature developed to solve this issue: Layered Mass Geometry (LMG) whereby both the standard (CT based patient geometry) and the parallel world (seeds and applicators) may now have mass. For any area where mass is present in the parallel world, the parallel mass is used. Elsewhere, the mass of the standard world is used. With LMG the user no longer needs to remove patient CT voxels that would include for example seeds. The patient representation can be a regular voxel grid, conducive to G4NestedParam, and the patient CT derived materials remain exact, avoiding the inaccuracy of the backfilling technique. Post-implant dosimetry for one patient with (125)I permanent seed implant was performed using Geant4 version 9.5.p01 using three different geometrical techniques. The first technique was the standard described above (G4PVPlacement). The second technique placed patient voxels as before, but placed seeds with LMG (G4PVPlacement+LMG). The third technique placed patient voxels through G4NestedParam and seeds through LMG (G4NestedParam+LMG). All the scenarios were calculated with 3 different image compression factors to manipulate the number of voxels. Additionally, the dosimetric impact of the backfilling technique was investigated for the case of calcifications in close proximity of sources. LMG eliminated the need for backfilling and simplified geometry description. Of the two LMG techniques, G4PVPlacement+LMG had no benefit to calculation time or memory use, actually increasing calculation time, but G4NestedParam+LMG reduced both calculation time and memory. The benefits of G4NestedParam+LMG over standard G4PVPlacement increased with increasing voxel numbers. For the case of calcifications in close proximity to sources, LMG not only increased efficiency but also yielded more accurate dose calculation than G4PVPlacement. G4NestedParam in combination with LMG present a new, efficient approach to simulate radiation sources that overlap patient geometry. Cases with brachytherapy applicators would constitute a direct extension of the method.},

keywords = {Brachytherapy, Computer-Assisted, Humans, Monte Carlo Method, Radiotherapy Dosage, Radiotherapy Planning},

pubstate = {published},

tppubtype = {article}

}

@article{enger_modeling_2011,

title = {Modeling a hypothetical 170Tm source for brachytherapy applications},

author = {Shirin A. Enger and Michel D'Amours and Luc Beaulieu},

doi = {10.1118/1.3626482},

issn = {0094-2405},

year  = {2011},

date = {2011-10-01},

journal = {Medical Physics},

volume = {38},

number = {10},

pages = {5307--5310},

abstract = {PURPOSE: To perform absorbed dose calculations based on Monte Carlo simulations for a hypothetical (170)Tm source and to investigate the influence of encapsulating material on the energy spectrum of the emitted electrons and photons. 

METHODS: GEANT4 Monte Carlo code version 9.2 patch 2 was used to simulate the decay process of (170)Tm and to calculate the absorbed dose distribution using the GEANT4 Penelope physics models. A hypothetical (170)Tm source based on the Flexisource brachytherapy design with the active core set as a pure thulium cylinder (length 3.5 mm and diameter 0.6 mm) and different cylindrical source encapsulations (length 5 mm and thickness 0.125 mm) constructed of titanium, stainless-steel, gold, or platinum were simulated. The radial dose function for the line source approximation was calculated following the TG-43U1 formalism for the stainless-steel encapsulation. 

RESULTS: For the titanium and stainless-steel encapsulation, 94% of the total bremsstrahlung is produced inside the core, 4.8 and 5.5% in titanium and stainless-steel capsules, respectively, and less than 1% in water. For the gold capsule, 85% is produced inside the core, 14.2% inside the gold capsule, and a negligible amount (textless1%) in water. Platinum encapsulation resulted in bremsstrahlung effects similar to those with the gold encapsulation. The range of the beta particles decreases by 1.1 mm with the stainless-steel encapsulation compared to the bare source but the tissue will still receive dose from the beta particles several millimeters from the source capsule. The gold and platinum capsules not only absorb most of the electrons but also attenuate low energy photons. The mean energy of the photons escaping the core and the stainless-steel capsule is 113 keV while for the gold and platinum the mean energy is 160 keV and 165 keV, respectively. 

CONCLUSIONS: A (170)Tm source is primarily a bremsstrahlung source, with the majority of bremsstrahlung photons being generated in the source core and experiencing little attenuation in the source encapsulation. Electrons are efficiently absorbed by the gold and platinum encapsulations. However, for the stainless-steel capsule (or other lower Z encapsulations) electrons will escape. The dose from these electrons is dominant over the photon dose in the first few millimeter but is not taken into account by current standard treatment planning systems. The total energy spectrum of photons emerging from the source depends on the encapsulation composition and results in mean photon energies well above 100 keV. This is higher than the main gamma-ray energy peak at 84 keV. Based on our results, the use of (170)Tm as a brachytherapy source presents notable challenges.},

keywords = {Algorithms, Brachytherapy, Computer Simulation, Computer-Assisted, Electrons, Equipment Design, Gold, Humans, Models, Monte Carlo Method, Photons, Platinum, Radioisotopes, Radiotherapy Planning, Stainless Steel, Theoretical, Thulium, Titanium},

pubstate = {published},

tppubtype = {article}

}

@article{enger_monte_2006,

title = {Monte Carlo calculations of thermal neutron capture in gadolinium: a comparison of GEANT4 and MCNP with measurements},

author = {Shirin A. Enger and Per Munck af Rosenschöld and Arash Rezaei and Hans Lundqvist},

doi = {10.1118/1.2150787},

issn = {0094-2405},

year  = {2006},

date = {2006-02-01},

journal = {Medical Physics},

volume = {33},

number = {2},

pages = {337--341},

abstract = {GEANT4 is a Monte Carlo code originally implemented for high-energy physics applications and is well known for particle transport at high energies. The capacity of GEANT4 to simulate neutron transport in the thermal energy region is not equally well known. The aim of this article is to compare MCNP, a code commonly used in low energy neutron transport calculations and GEANT4 with experimental results and select the suitable code for gadolinium neutron capture applications. To account for the thermal neutron scattering from chemically bound atoms [S(alpha,beta)] in biological materials a comparison of thermal neutron fluence in tissue-like poly(methylmethacrylate) phantom is made with MCNP4B, GEANT4 6.0 patch1, and measurements from the neutron capture therapy (NCT) facility at the Studsvik, Sweden. The fluence measurements agreed with MCNP calculated results considering S(alpha,beta). The location of the thermal neutron peak calculated with MCNP without S(alpha,beta) and GEANT4 is shifted by about 0.5 cm towards a shallower depth and is 25%-30% lower in amplitude. Dose distribution from the gadolinium neutron capture reaction is then simulated by MCNP and compared with measured data. The simulations made by MCNP agree well with experimental results. As long as thermal neutron scattering from chemically bound atoms are not included in GEANT4 it is not suitable for NCT applications.},

keywords = {Computer-Assisted, Fast Neutrons, Gadolinium, Humans, Imaging, Monte Carlo Method, Neutron Capture Therapy, Phantoms, Radiologic, Radiometry, Radiotherapy Planning, Reproducibility of Results, Technology},

pubstate = {published},

tppubtype = {article}

}

@article{enger_gadolinium_2006,

title = {Gadolinium neutron capture brachytherapy (GdNCB), a new treatment method for intravascular brachytherapy},

author = {Shirin A. Enger and Arash Rezaei and Per Munck af Rosenschöld and Hans Lundqvist},

doi = {10.1118/1.2146050},

issn = {0094-2405},

year  = {2006},

date = {2006-01-01},

journal = {Medical Physics},

volume = {33},

number = {1},

pages = {46--51},

abstract = {Restenosis is a major problem after balloon angioplasty and stent implantation. The aim of this study is to introduce gadolinium neutron capture brachytherapy (GdNCB) as a suitable modality for treatment of stenosis. The utility of GdNCB in intravascular brachytherapy (IVBT) of stent stenosis is investigated by using the GEANT4 and MCNP4B Monte Carlo radiation transport codes. To study capture rate, Kerma, absorbed dose and absorbed dose rate around a Gd-containing stent activated with neutrons, a 30 mm long, 5 mm diameter gadolinium foil is chosen. The input data is a neutron spectrum used for clinical neutron capture therapy in Studsvik, Sweden. Thermal neutron capture in gadolinium yields a spectrum of high-energy gamma photons, which due to the build-up effect gives an almost flat dose delivery pattern to the first 4 mm around the stent. The absorbed dose rate is 1.33 Gy/min, 0.25 mm from the stent surface while the dose to normal tissue is in order of 0.22 Gy/min, i.e., a factor of 6 lower. To spare normal tissue further fractionation of the dose is also possible. The capture rate is relatively high at both ends of the foil. The dose distribution from gamma and charge particle radiation at the edges and inside the stent contributes to a nonuniform dose distribution. This will lead to higher doses to the surrounding tissue and may prevent stent edge and in-stent restenosis. The position of the stent can be verified and corrected by the treatment plan prior to activation. Activation of the stent by an external neutron field can be performed days after catherization when the target cells start to proliferate and can be expected to be more radiation sensitive. Another advantage of the nonradioactive gadolinium stent is the possibility to avoid radiation hazard to personnel.},

keywords = {Biological, Blood Vessel Prosthesis, Brachytherapy, Computer Simulation, Computer-Assisted, Gadolinium, Graft Occlusion, Humans, Models, Monte Carlo Method, Neutron Capture Therapy, Radiometry, Radiotherapy Dosage, Radiotherapy Planning, Relative Biological Effectiveness, Statistical, Stents, Vascular},

pubstate = {published},

tppubtype = {article}

}