Maryam Rahbaran
PhD Student
Medical Physics Unit
Department of Oncology
Bio
Maryam is a PhD student in Dr. Enger’s lab. She has a B.Sc. in Combined Honours Physics and Astronomy from The University of British Columbia, and a M.Sc. in Medical Physics from McGill University.
Current Projects
Dosimetry for alpha- and beta-emitting radionuclide-based therapies
Targeted radionuclide-based therapies with alpha- and beta-emitters are of increasing interest for treating various cancers and rare diseases due to their abilities to deposit dose locally without affecting surrounding healthy tissue, compared to photons. However, the majority of radiobiology studies are based on photons, and dosimetric methods for studying the relative biological effectiveness of alpha and beta particles are not well-reported. In addition, dosimetry for nuclear medicine with alpha- and beta-emitting radionuclides varies with different clinical software, a quality assurance protocol is necessary to ensure accurate, patient-specific dosimetry with the gold standard Monte Carlo method as a validation tool. This project will focus on an analysis of the dosimetric properties of Am-241 in a custom alpha-particle irradiation set-up, and Sr-90 in a custom beta-particle irradiation set-up for radiobiology experiments. In addition, accurate Monte Carlo-based dosimetry of 3D printed phantoms will be performed, based on nuclear medicine patients injected with Lu-177 to serve as a standard to compare clinical dosimetry software to.
Publications/Awards
2025
Cyr, Mélodie; Rahbaran, Maryam; Tomic, Nada; Enger, Shirin A
Dosimetric evaluation of unlaminated radiochromic films exposed to an Americium-241 source using measurements and Monte Carlo simulations Journal Article
In: Medical Physics, vol. 52, iss. 11, no. e70001, 2025, ISSN: 2473-4209.
@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}
}
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.
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.
Rahbaran, Maryam; Li, Joanna; Enger, Shirin A.
Monte Carlo-based dosimetry and optimization of a custom alpha cell irradiation setup Journal Article
In: Physics in Medicine & Biology, vol. 70, iss. 13, no. 135011, 2025, ISSN: 1361-6560.
@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}
}
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.
2024
Rahbaran, Maryam; Kalinowski, Jonathan; DeCunha, Joseph M.; Croce, Kevin J.; Bergmark, Brian A.; Tsui, James M. G.; Devlin, Phillip M.; Enger, Shirin A.
RapidBrachyIVBT: A dosimetry software for patient-specific intravascular brachytherapy dose calculations on optical coherence tomography images Journal Article
In: Medical Physics, vol. 52, iss. 2, pp. 1256-1267, 2024, ISSN: 2473-4209.
@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}
}
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.
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.
2023
Rahbaran, Maryam; Kalinowski, Jonathan; DeCunha, Joseph; Croce, Kevin; Bergmark, Brian; Devlin, Philip; Tsui, James; Enger, Shirin A.
Development Of a Novel Dosimetry Software for Patient-specific Intravascular Brachytherapy Treatment Planning on Optical Coherence Tomography Images Presentation
23.09.2023, (COMP-CARO 2023 Joint Scientific Meeting).
@misc{nokey,
title = {Development Of a Novel Dosimetry Software for Patient-specific Intravascular Brachytherapy Treatment Planning on Optical Coherence Tomography Images},
author = {Maryam Rahbaran and Jonathan Kalinowski and Joseph DeCunha and Kevin Croce and Brian Bergmark and Philip Devlin and James Tsui and Shirin A. Enger},
year = {2023},
date = {2023-09-23},
note = {COMP-CARO 2023 Joint Scientific Meeting},
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pubstate = {published},
tppubtype = {presentation}
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Rahbaran, Maryam; Kalinowski, Jonathan; Tsui, James; DeCunha, Joseph; Croce, Kevin; Bergmark, Brian; Devlin, Philip; Enger, Shirin A.
Development Of a Novel Dosimetry Software for Patient-specific Intravascular Brachytherapy Treatment Planning on Optical Coherence Tomography Images Presentation
22.06.2023, (2023 American Brachytherapy Society (ABS) Annual Meeting, Vancouver, Canada).
@misc{nokey,
title = {Development Of a Novel Dosimetry Software for Patient-specific Intravascular Brachytherapy Treatment Planning on Optical Coherence Tomography Images},
author = {Maryam Rahbaran and Jonathan Kalinowski and James Tsui and Joseph DeCunha and Kevin Croce and Brian Bergmark and Philip Devlin and Shirin A. Enger},
year = {2023},
date = {2023-06-22},
urldate = {2023-06-22},
note = {2023 American Brachytherapy Society (ABS) Annual Meeting, Vancouver, Canada},
keywords = {},
pubstate = {published},
tppubtype = {presentation}
}
2022
Rahbaran, Maryam
Graduate Excellence Award award
2022.
@award{nokey,
title = {Graduate Excellence Award },
author = {Maryam Rahbaran},
year = {2022},
date = {2022-08-08},
abstract = {Merit-based recruitment award for first year MSc students. },
keywords = {},
pubstate = {published},
tppubtype = {award}
}
Merit-based recruitment award for first year MSc students.
Rahbaran, Maryam; Kalinowski, Jonathan; Tsui, James; DeCunha, Joseph; Enger, Shirin A.
Monte-Carlo Based Simulations of the Uncertainties in Clinical Water-Based Intravascular Brachytherapy Dosimetry Presentation
11.04.2022.
@misc{nokey,
title = {Monte-Carlo Based Simulations of the Uncertainties in Clinical Water-Based Intravascular Brachytherapy Dosimetry},
author = {Maryam Rahbaran and Jonathan Kalinowski and James Tsui and Joseph DeCunha and Shirin A. Enger},
year = {2022},
date = {2022-04-11},
urldate = {2022-04-11},
journal = {MCMA},
abstract = {"Introduction
Coronary artery disease (CAD) is the most common form of cardiovascular disease and is caused by excess plaque along the arterial wall, blocking blood flow to the heart (stenosis). Percutaneous transluminal coronary angioplasty widens a narrowed artery, leaving behind metal stents (1). However, in-stent restenosis (ISR) may occur due to damage to the arterial wall tissue, triggering neointimal hyperplasia which produces fibrotic and calcified plaques, narrowing the artery again. Drug-eluting stents (DES) slowly release medication to inhibit neointimal hyperplasia to prevent ISR but they fail in 3% to 20% of cases (2). Intravascular brachytherapy (IVBT), which uses b-emitting radionuclides to prevent ISR, is used in these failed cases. However, current dosimetry for IVBT is water based and does not consider attenuation of the radiation by heterogeneities such as the IVBT device guidewire, non-uniform distribution of calcified plaques, and stent material, or the angular dependence of dose distribution (3, 4, 5). The aim of this study was to investigate the uncertainties in clinical water based IVBT dosimetry, considering the effect of heterogeneities on dose distribution.
Materials & Methods
An inhouse Monte-Carlo based dosimetry package for IVBT applications based on Geant4 10.04 (patch 2) was developed. Patient’s artery was modelled as a 32 mm long, 8.4 mm diameter cylinder comprised of three layers: tunica media, represented with muscle, tunica intima, represented with fibrotic plaque, and tunica adventitia, represented with collagen. These layers had mass densities 1.06 g/cm3, 1.22 g/cm3 and 1.07 g/cm3 respectively. The innermost layer consisted of calcified plaque of density 1.45 g/cm3 with varying thicknesses between 0.9 and 1.9 mm with an eccentric shape and a rough surface. The stents had similar composition to Boston Scientific Synergy stents and were modelled to not overlap. The Novoste Beta-Cath 3.5F IVBT device model was used, which has a 90Sr90Y source. The geometry is shown in Figure 1a. A cylindrical scoring geometry was implemented. Two set of simulations were performed. In the first simulation called water phantom, the entire system consisted of water with unit density, and dose to water was calculated similar to the clinical water based dosimetry. In the second simulation called the artery model proper material and mass densities were assigned to each component. To ensure uncertainties below 0.8% within a 1 mm radial distance to the source and 2% within 4.2 mm from the source, 100 million decay events were simulated. The Penelope physics list was used to simulate the electromagnetic interactions between particles. Average, minimum, and maximum dose was calculated at 2.0 mm from the source center and directly and 1 mm behind the outermost stents and guidewire. Absorbed dose was normalized to 23 Gy at 2.0 mm from the source center.
Results
International Conference on Monte Carlo Techniques for Medical Applications, 2022
Compared to the water phantom (Figure 1b), average dose in the artery model (Figure 1c) was attenuated by 50.9% at 2 mm from the source centre and directly behind the guidewire and outermost stent by 66.2%, and by 69.5% 1 mm behind this region. There was significant variation in dose around the source due to the guidewire attenuating dose the most, and heterogeneous distribution of calcification.
Discussion & Conclusions
Dosimetry for IVBT based on dose rate in water is not accurate. Heterogeneities need to be considered to deliver adequate dose to the lesion area. Stent material, heterogenous distribution of calcification and the off cantered placement of the guidewire affects the uniformity of dose distribution around the source. Patients may benefit from personalized treatment planning taking dose-attenuating by different tissue/material heterogeneities into account.
References
[1] Virani, Salim, S., et al. ""Heart Disease and Stroke Statistics—2020 Update"". Circulation, vol. 141, no. 9, March 03, 2020, pp. e336. doi: 10.1161/CIR.0000000000000757.
[2] Lee M, Banka G. In-stent restenosis. Interv Cardiol Clin 2016;5: 211e220.
[3] Chiu-Tsao ST, Schaart DR, Soares CG, et al. Dose calculation formalisms and consensus dosimetry parameters for intravascular brachytherapy dosimetry: Recommendations of the AAPM Therapy Physics Committee Task Group No. 149. Med Phys 2007;34: 4126e4157.
[4] Rivard MJ, Coursey BM, DeWerd LA, et al. Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations. Med Phys 2004;31:633e674.
[5] Nath R, Amols H, Coffey C, et al. Intravascular brachytherapy physics: Report of the AAPM Radiation Therapy Committee Task group No. 60. Med Phys 1999;26:119e152.’
[6] Agostinelli S, Allison J, Amako K, et al. Geant4da simulation toolkit. Nucl Instrum Methods Phys Res 2003;506:230e303."},
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pubstate = {published},
tppubtype = {presentation}
}
"Introduction
Coronary artery disease (CAD) is the most common form of cardiovascular disease and is caused by excess plaque along the arterial wall, blocking blood flow to the heart (stenosis). Percutaneous transluminal coronary angioplasty widens a narrowed artery, leaving behind metal stents (1). However, in-stent restenosis (ISR) may occur due to damage to the arterial wall tissue, triggering neointimal hyperplasia which produces fibrotic and calcified plaques, narrowing the artery again. Drug-eluting stents (DES) slowly release medication to inhibit neointimal hyperplasia to prevent ISR but they fail in 3% to 20% of cases (2). Intravascular brachytherapy (IVBT), which uses b-emitting radionuclides to prevent ISR, is used in these failed cases. However, current dosimetry for IVBT is water based and does not consider attenuation of the radiation by heterogeneities such as the IVBT device guidewire, non-uniform distribution of calcified plaques, and stent material, or the angular dependence of dose distribution (3, 4, 5). The aim of this study was to investigate the uncertainties in clinical water based IVBT dosimetry, considering the effect of heterogeneities on dose distribution.
Materials & Methods
An inhouse Monte-Carlo based dosimetry package for IVBT applications based on Geant4 10.04 (patch 2) was developed. Patient’s artery was modelled as a 32 mm long, 8.4 mm diameter cylinder comprised of three layers: tunica media, represented with muscle, tunica intima, represented with fibrotic plaque, and tunica adventitia, represented with collagen. These layers had mass densities 1.06 g/cm3, 1.22 g/cm3 and 1.07 g/cm3 respectively. The innermost layer consisted of calcified plaque of density 1.45 g/cm3 with varying thicknesses between 0.9 and 1.9 mm with an eccentric shape and a rough surface. The stents had similar composition to Boston Scientific Synergy stents and were modelled to not overlap. The Novoste Beta-Cath 3.5F IVBT device model was used, which has a 90Sr90Y source. The geometry is shown in Figure 1a. A cylindrical scoring geometry was implemented. Two set of simulations were performed. In the first simulation called water phantom, the entire system consisted of water with unit density, and dose to water was calculated similar to the clinical water based dosimetry. In the second simulation called the artery model proper material and mass densities were assigned to each component. To ensure uncertainties below 0.8% within a 1 mm radial distance to the source and 2% within 4.2 mm from the source, 100 million decay events were simulated. The Penelope physics list was used to simulate the electromagnetic interactions between particles. Average, minimum, and maximum dose was calculated at 2.0 mm from the source center and directly and 1 mm behind the outermost stents and guidewire. Absorbed dose was normalized to 23 Gy at 2.0 mm from the source center.
Results
International Conference on Monte Carlo Techniques for Medical Applications, 2022
Compared to the water phantom (Figure 1b), average dose in the artery model (Figure 1c) was attenuated by 50.9% at 2 mm from the source centre and directly behind the guidewire and outermost stent by 66.2%, and by 69.5% 1 mm behind this region. There was significant variation in dose around the source due to the guidewire attenuating dose the most, and heterogeneous distribution of calcification.
Discussion & Conclusions
Dosimetry for IVBT based on dose rate in water is not accurate. Heterogeneities need to be considered to deliver adequate dose to the lesion area. Stent material, heterogenous distribution of calcification and the off cantered placement of the guidewire affects the uniformity of dose distribution around the source. Patients may benefit from personalized treatment planning taking dose-attenuating by different tissue/material heterogeneities into account.
References
[1] Virani, Salim, S., et al. ""Heart Disease and Stroke Statistics—2020 Update"". Circulation, vol. 141, no. 9, March 03, 2020, pp. e336. doi: 10.1161/CIR.0000000000000757.
[2] Lee M, Banka G. In-stent restenosis. Interv Cardiol Clin 2016;5: 211e220.
[3] Chiu-Tsao ST, Schaart DR, Soares CG, et al. Dose calculation formalisms and consensus dosimetry parameters for intravascular brachytherapy dosimetry: Recommendations of the AAPM Therapy Physics Committee Task Group No. 149. Med Phys 2007;34: 4126e4157.
[4] Rivard MJ, Coursey BM, DeWerd LA, et al. Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations. Med Phys 2004;31:633e674.
[5] Nath R, Amols H, Coffey C, et al. Intravascular brachytherapy physics: Report of the AAPM Radiation Therapy Committee Task group No. 60. Med Phys 1999;26:119e152.’
[6] Agostinelli S, Allison J, Amako K, et al. Geant4da simulation toolkit. Nucl Instrum Methods Phys Res 2003;506:230e303."
Coronary artery disease (CAD) is the most common form of cardiovascular disease and is caused by excess plaque along the arterial wall, blocking blood flow to the heart (stenosis). Percutaneous transluminal coronary angioplasty widens a narrowed artery, leaving behind metal stents (1). However, in-stent restenosis (ISR) may occur due to damage to the arterial wall tissue, triggering neointimal hyperplasia which produces fibrotic and calcified plaques, narrowing the artery again. Drug-eluting stents (DES) slowly release medication to inhibit neointimal hyperplasia to prevent ISR but they fail in 3% to 20% of cases (2). Intravascular brachytherapy (IVBT), which uses b-emitting radionuclides to prevent ISR, is used in these failed cases. However, current dosimetry for IVBT is water based and does not consider attenuation of the radiation by heterogeneities such as the IVBT device guidewire, non-uniform distribution of calcified plaques, and stent material, or the angular dependence of dose distribution (3, 4, 5). The aim of this study was to investigate the uncertainties in clinical water based IVBT dosimetry, considering the effect of heterogeneities on dose distribution.
Materials & Methods
An inhouse Monte-Carlo based dosimetry package for IVBT applications based on Geant4 10.04 (patch 2) was developed. Patient’s artery was modelled as a 32 mm long, 8.4 mm diameter cylinder comprised of three layers: tunica media, represented with muscle, tunica intima, represented with fibrotic plaque, and tunica adventitia, represented with collagen. These layers had mass densities 1.06 g/cm3, 1.22 g/cm3 and 1.07 g/cm3 respectively. The innermost layer consisted of calcified plaque of density 1.45 g/cm3 with varying thicknesses between 0.9 and 1.9 mm with an eccentric shape and a rough surface. The stents had similar composition to Boston Scientific Synergy stents and were modelled to not overlap. The Novoste Beta-Cath 3.5F IVBT device model was used, which has a 90Sr90Y source. The geometry is shown in Figure 1a. A cylindrical scoring geometry was implemented. Two set of simulations were performed. In the first simulation called water phantom, the entire system consisted of water with unit density, and dose to water was calculated similar to the clinical water based dosimetry. In the second simulation called the artery model proper material and mass densities were assigned to each component. To ensure uncertainties below 0.8% within a 1 mm radial distance to the source and 2% within 4.2 mm from the source, 100 million decay events were simulated. The Penelope physics list was used to simulate the electromagnetic interactions between particles. Average, minimum, and maximum dose was calculated at 2.0 mm from the source center and directly and 1 mm behind the outermost stents and guidewire. Absorbed dose was normalized to 23 Gy at 2.0 mm from the source center.
Results
International Conference on Monte Carlo Techniques for Medical Applications, 2022
Compared to the water phantom (Figure 1b), average dose in the artery model (Figure 1c) was attenuated by 50.9% at 2 mm from the source centre and directly behind the guidewire and outermost stent by 66.2%, and by 69.5% 1 mm behind this region. There was significant variation in dose around the source due to the guidewire attenuating dose the most, and heterogeneous distribution of calcification.
Discussion & Conclusions
Dosimetry for IVBT based on dose rate in water is not accurate. Heterogeneities need to be considered to deliver adequate dose to the lesion area. Stent material, heterogenous distribution of calcification and the off cantered placement of the guidewire affects the uniformity of dose distribution around the source. Patients may benefit from personalized treatment planning taking dose-attenuating by different tissue/material heterogeneities into account.
References
[1] Virani, Salim, S., et al. ""Heart Disease and Stroke Statistics—2020 Update"". Circulation, vol. 141, no. 9, March 03, 2020, pp. e336. doi: 10.1161/CIR.0000000000000757.
[2] Lee M, Banka G. In-stent restenosis. Interv Cardiol Clin 2016;5: 211e220.
[3] Chiu-Tsao ST, Schaart DR, Soares CG, et al. Dose calculation formalisms and consensus dosimetry parameters for intravascular brachytherapy dosimetry: Recommendations of the AAPM Therapy Physics Committee Task Group No. 149. Med Phys 2007;34: 4126e4157.
[4] Rivard MJ, Coursey BM, DeWerd LA, et al. Update of AAPM Task Group No. 43 Report: A revised AAPM protocol for brachytherapy dose calculations. Med Phys 2004;31:633e674.
[5] Nath R, Amols H, Coffey C, et al. Intravascular brachytherapy physics: Report of the AAPM Radiation Therapy Committee Task group No. 60. Med Phys 1999;26:119e152.’
[6] Agostinelli S, Allison J, Amako K, et al. Geant4da simulation toolkit. Nucl Instrum Methods Phys Res 2003;506:230e303."