Journal Articles
2021
Morcos, Marc; Antaki, Majd; Viswanathan, Akila N.; Enger, Shirin A.
A novel minimally invasive dynamic-shield, intensity-modulated brachytherapy system for the treatment of cervical cancer Journal Article
In: Medical Physics, vol. 48, no. 1, pp. 71–79, 2021, ISSN: 2473-4209.
Abstract | Links | BibTeX | Tags: 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
@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}
}
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.2020
Morcos, Marc; Enger, Shirin A.
Monte Carlo dosimetry study of novel rotating MRI-compatible shielded tandems for intensity modulated cervix brachytherapy Journal Article
In: 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), vol. 71, pp. 178–184, 2020, ISSN: 1724-191X.
Abstract | Links | BibTeX | Tags: Anisotropy, Brachytherapy, Female, Humans, Image-guided cervix brachytherapy, Intensity modulated brachytherapy, Intensity-Modulated, Iridium Radioisotopes, Magnetic Resonance Imaging, Monte Carlo based dosimetry, Monte Carlo Method, MRI-guided GYN brachytherapy, Radiometry, Radiotherapy, Selenium Radioisotopes, Uterine Cervical Neoplasms, Ytterbium
@article{morcos_monte_2020,
title = {Monte Carlo dosimetry study of novel rotating MRI-compatible shielded tandems for intensity modulated cervix brachytherapy},
author = {Marc Morcos and Shirin A. Enger},
doi = {10.1016/j.ejmp.2020.02.014},
issn = {1724-191X},
year = {2020},
date = {2020-03-01},
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 = {71},
pages = {178--184},
abstract = {PURPOSE: Intensity modulated brachytherapy (IMBT) with rotating metal shields enables dose modulation that can better conform to the tumor while reducing OAR doses. In this work, we investigate novel rotating shields, compatible with MRI-compatible tandems used for cervix brachytherapy. Three unique shields were evaluated using the traditional 192Ir source. Additionally, 75Se and 169Yb isotopes were investigated as alternative sources.
METHODS: Three different IMBT shields were modeled and simulated in RapidBrachyMCTPS. Each tungsten shield was designed to fit inside a 6 mm-wide MRI-compatible tandem. The active core of the source was replaced with 192Ir, 75Se and 169Yb. Transmission factors (TFs) were calculated and defined as the dose ratio at 1 cm on opposite sides of the shielded tandem on the transverse plane. Polar and azimuthal anisotropy plots were extracted from simulations. Dose homogeneities V200%V100% were calculated for all radionuclide-shield combinations.
RESULTS: TFs are favorable for IMBT and ranged between 12.9% and 32.2% for 192Ir, 4.0%-16.1% for 75Se and 1.2-6.4% for 169Yb for all shield designs. Average beam-widths in the polar and azimuthal directions were reduced to the range of 42°-112° and 27°-107°, respectively, for all shield-radionuclide combinations. Dose homogeneities for all the radionuclide-shield combinations were within 12% of the non-IMBT tandem.
CONCLUSIONS: This study has quantitatively assessed the influence of various rotating cervical cancer-specific IMBT tandem shields on dosimetry. The dynamic single-channel shields and narrow beam-widths in the polar and azimuthal direction give rise to highly anisotropic distributions. Intermediate-to-high energy radionuclides, 75Se and 169Yb substantially improve the modulation capacity of IMBT and pave the way for treating large and complex cervical cancer without interstitial needle implantation.},
keywords = {Anisotropy, Brachytherapy, Female, Humans, Image-guided cervix brachytherapy, Intensity modulated brachytherapy, Intensity-Modulated, Iridium Radioisotopes, Magnetic Resonance Imaging, Monte Carlo based dosimetry, Monte Carlo Method, MRI-guided GYN brachytherapy, Radiometry, Radiotherapy, Selenium Radioisotopes, Uterine Cervical Neoplasms, Ytterbium},
pubstate = {published},
tppubtype = {article}
}
PURPOSE: Intensity modulated brachytherapy (IMBT) with rotating metal shields enables dose modulation that can better conform to the tumor while reducing OAR doses. In this work, we investigate novel rotating shields, compatible with MRI-compatible tandems used for cervix brachytherapy. Three unique shields were evaluated using the traditional 192Ir source. Additionally, 75Se and 169Yb isotopes were investigated as alternative sources.
METHODS: Three different IMBT shields were modeled and simulated in RapidBrachyMCTPS. Each tungsten shield was designed to fit inside a 6 mm-wide MRI-compatible tandem. The active core of the source was replaced with 192Ir, 75Se and 169Yb. Transmission factors (TFs) were calculated and defined as the dose ratio at 1 cm on opposite sides of the shielded tandem on the transverse plane. Polar and azimuthal anisotropy plots were extracted from simulations. Dose homogeneities V200%V100% were calculated for all radionuclide-shield combinations.
RESULTS: TFs are favorable for IMBT and ranged between 12.9% and 32.2% for 192Ir, 4.0%-16.1% for 75Se and 1.2-6.4% for 169Yb for all shield designs. Average beam-widths in the polar and azimuthal directions were reduced to the range of 42°-112° and 27°-107°, respectively, for all shield-radionuclide combinations. Dose homogeneities for all the radionuclide-shield combinations were within 12% of the non-IMBT tandem.
CONCLUSIONS: This study has quantitatively assessed the influence of various rotating cervical cancer-specific IMBT tandem shields on dosimetry. The dynamic single-channel shields and narrow beam-widths in the polar and azimuthal direction give rise to highly anisotropic distributions. Intermediate-to-high energy radionuclides, 75Se and 169Yb substantially improve the modulation capacity of IMBT and pave the way for treating large and complex cervical cancer without interstitial needle implantation.Presentations
2021
Morcos, Marc; Enger, Shirin A.
MR-guided intensity modulated brachytherapy for gynecologic cancers Presentation
McGill FMT, 01.01.2021.
BibTeX | Tags: Image-guided cervix brachytherapy, Intensity modulated brachytherapy, Monte Carlo based dosimetry, MRI-guided GYN brachytherapy
@misc{Morcos2021,
title = {MR-guided intensity modulated brachytherapy for gynecologic cancers},
author = {Marc Morcos and Shirin A. Enger},
year = {2021},
date = {2021-01-01},
howpublished = {McGill FMT},
keywords = {Image-guided cervix brachytherapy, Intensity modulated brachytherapy, Monte Carlo based dosimetry, MRI-guided GYN brachytherapy},
pubstate = {published},
tppubtype = {presentation}
}
Journal Articles
2021
Morcos, Marc; Antaki, Majd; Viswanathan, Akila N.; Enger, Shirin A.
A novel minimally invasive dynamic-shield, intensity-modulated brachytherapy system for the treatment of cervical cancer Journal Article
In: Medical Physics, vol. 48, no. 1, pp. 71–79, 2021, ISSN: 2473-4209.
Abstract | Links | BibTeX | Tags: 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
@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}
}
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.
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.
2020
Morcos, Marc; Enger, Shirin A.
Monte Carlo dosimetry study of novel rotating MRI-compatible shielded tandems for intensity modulated cervix brachytherapy Journal Article
In: 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), vol. 71, pp. 178–184, 2020, ISSN: 1724-191X.
Abstract | Links | BibTeX | Tags: Anisotropy, Brachytherapy, Female, Humans, Image-guided cervix brachytherapy, Intensity modulated brachytherapy, Intensity-Modulated, Iridium Radioisotopes, Magnetic Resonance Imaging, Monte Carlo based dosimetry, Monte Carlo Method, MRI-guided GYN brachytherapy, Radiometry, Radiotherapy, Selenium Radioisotopes, Uterine Cervical Neoplasms, Ytterbium
@article{morcos_monte_2020,
title = {Monte Carlo dosimetry study of novel rotating MRI-compatible shielded tandems for intensity modulated cervix brachytherapy},
author = {Marc Morcos and Shirin A. Enger},
doi = {10.1016/j.ejmp.2020.02.014},
issn = {1724-191X},
year = {2020},
date = {2020-03-01},
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 = {71},
pages = {178--184},
abstract = {PURPOSE: Intensity modulated brachytherapy (IMBT) with rotating metal shields enables dose modulation that can better conform to the tumor while reducing OAR doses. In this work, we investigate novel rotating shields, compatible with MRI-compatible tandems used for cervix brachytherapy. Three unique shields were evaluated using the traditional 192Ir source. Additionally, 75Se and 169Yb isotopes were investigated as alternative sources.
METHODS: Three different IMBT shields were modeled and simulated in RapidBrachyMCTPS. Each tungsten shield was designed to fit inside a 6 mm-wide MRI-compatible tandem. The active core of the source was replaced with 192Ir, 75Se and 169Yb. Transmission factors (TFs) were calculated and defined as the dose ratio at 1 cm on opposite sides of the shielded tandem on the transverse plane. Polar and azimuthal anisotropy plots were extracted from simulations. Dose homogeneities V200%V100% were calculated for all radionuclide-shield combinations.
RESULTS: TFs are favorable for IMBT and ranged between 12.9% and 32.2% for 192Ir, 4.0%-16.1% for 75Se and 1.2-6.4% for 169Yb for all shield designs. Average beam-widths in the polar and azimuthal directions were reduced to the range of 42°-112° and 27°-107°, respectively, for all shield-radionuclide combinations. Dose homogeneities for all the radionuclide-shield combinations were within 12% of the non-IMBT tandem.
CONCLUSIONS: This study has quantitatively assessed the influence of various rotating cervical cancer-specific IMBT tandem shields on dosimetry. The dynamic single-channel shields and narrow beam-widths in the polar and azimuthal direction give rise to highly anisotropic distributions. Intermediate-to-high energy radionuclides, 75Se and 169Yb substantially improve the modulation capacity of IMBT and pave the way for treating large and complex cervical cancer without interstitial needle implantation.},
keywords = {Anisotropy, Brachytherapy, Female, Humans, Image-guided cervix brachytherapy, Intensity modulated brachytherapy, Intensity-Modulated, Iridium Radioisotopes, Magnetic Resonance Imaging, Monte Carlo based dosimetry, Monte Carlo Method, MRI-guided GYN brachytherapy, Radiometry, Radiotherapy, Selenium Radioisotopes, Uterine Cervical Neoplasms, Ytterbium},
pubstate = {published},
tppubtype = {article}
}
PURPOSE: Intensity modulated brachytherapy (IMBT) with rotating metal shields enables dose modulation that can better conform to the tumor while reducing OAR doses. In this work, we investigate novel rotating shields, compatible with MRI-compatible tandems used for cervix brachytherapy. Three unique shields were evaluated using the traditional 192Ir source. Additionally, 75Se and 169Yb isotopes were investigated as alternative sources.
METHODS: Three different IMBT shields were modeled and simulated in RapidBrachyMCTPS. Each tungsten shield was designed to fit inside a 6 mm-wide MRI-compatible tandem. The active core of the source was replaced with 192Ir, 75Se and 169Yb. Transmission factors (TFs) were calculated and defined as the dose ratio at 1 cm on opposite sides of the shielded tandem on the transverse plane. Polar and azimuthal anisotropy plots were extracted from simulations. Dose homogeneities V200%V100% were calculated for all radionuclide-shield combinations.
RESULTS: TFs are favorable for IMBT and ranged between 12.9% and 32.2% for 192Ir, 4.0%-16.1% for 75Se and 1.2-6.4% for 169Yb for all shield designs. Average beam-widths in the polar and azimuthal directions were reduced to the range of 42°-112° and 27°-107°, respectively, for all shield-radionuclide combinations. Dose homogeneities for all the radionuclide-shield combinations were within 12% of the non-IMBT tandem.
CONCLUSIONS: This study has quantitatively assessed the influence of various rotating cervical cancer-specific IMBT tandem shields on dosimetry. The dynamic single-channel shields and narrow beam-widths in the polar and azimuthal direction give rise to highly anisotropic distributions. Intermediate-to-high energy radionuclides, 75Se and 169Yb substantially improve the modulation capacity of IMBT and pave the way for treating large and complex cervical cancer without interstitial needle implantation.
METHODS: Three different IMBT shields were modeled and simulated in RapidBrachyMCTPS. Each tungsten shield was designed to fit inside a 6 mm-wide MRI-compatible tandem. The active core of the source was replaced with 192Ir, 75Se and 169Yb. Transmission factors (TFs) were calculated and defined as the dose ratio at 1 cm on opposite sides of the shielded tandem on the transverse plane. Polar and azimuthal anisotropy plots were extracted from simulations. Dose homogeneities V200%V100% were calculated for all radionuclide-shield combinations.
RESULTS: TFs are favorable for IMBT and ranged between 12.9% and 32.2% for 192Ir, 4.0%-16.1% for 75Se and 1.2-6.4% for 169Yb for all shield designs. Average beam-widths in the polar and azimuthal directions were reduced to the range of 42°-112° and 27°-107°, respectively, for all shield-radionuclide combinations. Dose homogeneities for all the radionuclide-shield combinations were within 12% of the non-IMBT tandem.
CONCLUSIONS: This study has quantitatively assessed the influence of various rotating cervical cancer-specific IMBT tandem shields on dosimetry. The dynamic single-channel shields and narrow beam-widths in the polar and azimuthal direction give rise to highly anisotropic distributions. Intermediate-to-high energy radionuclides, 75Se and 169Yb substantially improve the modulation capacity of IMBT and pave the way for treating large and complex cervical cancer without interstitial needle implantation.
Presentations
2021
Morcos, Marc; Enger, Shirin A.
MR-guided intensity modulated brachytherapy for gynecologic cancers Presentation
McGill FMT, 01.01.2021.
BibTeX | Tags: Image-guided cervix brachytherapy, Intensity modulated brachytherapy, Monte Carlo based dosimetry, MRI-guided GYN brachytherapy
@misc{Morcos2021,
title = {MR-guided intensity modulated brachytherapy for gynecologic cancers},
author = {Marc Morcos and Shirin A. Enger},
year = {2021},
date = {2021-01-01},
howpublished = {McGill FMT},
keywords = {Image-guided cervix brachytherapy, Intensity modulated brachytherapy, Monte Carlo based dosimetry, MRI-guided GYN brachytherapy},
pubstate = {published},
tppubtype = {presentation}
}