Monte Carlo dosimetry study of novel rotating MRI-compatible shielded tandems for intensity modulated cervix brachytherapy

Morcos, Marc; Enger, Shirin A.

doi:10.1016/j.ejmp.2020.02.014

Cited by 11 publications

(22 citation statements)

References 28 publications

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“…A full characterization of this IMBT tandem has been investigated in detail in a previous study. 8 D m,m distributions for conventional tandem HDR BT with 192 Ir as the radiation source and the IMBT tandem with 192 Ir, 75 Se, and 169 Yb as radiation sources are shown in Fig. 3 for case #22.…”

Section: Resultsmentioning

confidence: 99%

“…Despite the lower energy of 169 Yb, the modest decrease in DHI 150 and DHI 200 (0.02 and 0.05, relative to conventional 192 Ir-based BT) is due to its favorable radial dose function. 8 It is important to note that due to the absence of needles, the IMBT dose is hottest in the center of the cervix and not in normal tissue. To put this in perspective, Kirisits et al noted an increase to the 200% isodose volume from 25 to 33 cm 3 , a 32% change, when adding interstitial needles to the tandem and ring.…”

Section: Discussionmentioning

confidence: 99%

“…Further details of the mechanical design of the IMBT delivery system are described in a previous publication. 8…”

Section: A Imbt Cervix Applicator and Shield Designmentioning

confidence: 99%

“…The MRI-compatible IMBT delivery prototype system for treatment of cervical cancer used in this study builds on our prior work. 8,19 2. MATERIALS AND METHODS…”

Section: Introductionmentioning

confidence: 99%

“…Examples include static directional modulated BT (DMBT) and dynamic shield intensity modulated BT (IMBT), referred to herein simply as IMBT. [6][7][8][9] With DMBT, a static metal alloy shield placed inside conventional applicators enable anisotropic dose distributions, which have been shown to decrease OAR doses in rectal and cervical cancer BT. 10,11 The IMBT technique uses metallic shields which can rotate during the treatment, independent of the applicator that they are contained in, and allow for dynamic directional control of the radiation emission.…”

Section: Introductionmentioning

confidence: 99%

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A novel minimally invasive dynamic‐shield, intensity‐modulated brachytherapy system for the treatment of cervical cancer

et al. 2020

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Purpose To present a novel, MRI‐compatible dynamicshield intensity modulated brachytherapy (IMBT) applicator and delivery system using 192Ir, 75Se, and 169Yb 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 192Ir) plans were compared to IMBT (10Ci 192Ir; 11.5Ci 75Se; 44Ci 169Yb). 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 < 0.001) and 6.7% ± 0.5% (P < 0.001), respectively, with the largest dosimetric enhancement when using 169Yb followed by 75Se and then 192Ir. Similarly, D2cc for all OAR improved with IMBT by up to 7.7% ± 0.6% (P < 0.001). For IC/IS‐BT cases, needle‐free IMBT achieved clinically acceptable plans with 169Yb‐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 192Ir, 75Se, and 169Yb, respectively, relative to conventional 192Ir 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.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

“…Further details of the mechanical design of the IMBT delivery system are described in a previous publication. 8…”

Section: A Imbt Cervix Applicator and Shield Designmentioning

confidence: 99%

“…The MRI-compatible IMBT delivery prototype system for treatment of cervical cancer used in this study builds on our prior work. 8,19 2. MATERIALS AND METHODS…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A novel minimally invasive dynamic‐shield, intensity‐modulated brachytherapy system for the treatment of cervical cancer

et al. 2020

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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

2021

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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 intensitymodulated 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 (D w,w ); (b) D w,w taking the applicator material into consideration (D w,wApp ); (c) dose to water in medium (D w,m ); (d and e) dose to medium in medium with mass densities assigned either nominally per structure (D m,m (Nom) ) or voxel-by-voxel (D m,m ).Results: Ignoring the plastic Venezia applicator (D w,wApp ) overestimates D m,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 (D w,wApp or D w,m ) generally overestimates dose and this effect increases with decreasing photon energy. Reporting dose other than D m,m (or D m,m Nom ) for 169 Yb-based conventional and intensity-modulated brachytherapy leads to a simultaneous overestimation (up to 4%) of CTV HR D 90 and underestimation (up to 2%) of bladder D 2cc 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 D m,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 D w,m and D w,w may overstate the dosimetric benefits.

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AAPM WGDCAB Report 372: A joint AAPM, ESTRO, ABG, and ABS report on commissioning of model‐based dose calculation algorithms in brachytherapy

et al. 2023

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The introduction of model‐based dose calculation algorithms (MBDCAs) in brachytherapy provides an opportunity for a more accurate dose calculation and opens the possibility for novel, innovative treatment modalities. The joint AAPM, ESTRO, and ABG Task Group 186 (TG‐186) report provided guidance to early adopters. However, the commissioning aspect of these algorithms was described only in general terms with no quantitative goals. This report, from the Working Group on Model‐Based Dose Calculation Algorithms in Brachytherapy, introduced a field‐tested approach to MBDCA commissioning. It is based on a set of well‐characterized test cases for which reference Monte Carlo (MC) and vendor‐specific MBDCA dose distributions are available in a Digital Imaging and Communications in Medicine—Radiotherapy (DICOM‐RT) format to the clinical users. The key elements of the TG‐186 commissioning workflow are now described in detail, and quantitative goals are provided. This approach leverages the well‐known Brachytherapy Source Registry jointly managed by the AAPM and the Imaging and Radiation Oncology Core (IROC) Houston Quality Assurance Center (with associated links at ESTRO) to provide open access to test cases as well as step‐by‐step user guides. While the current report is limited to the two most widely commercially available MBDCAs and only for 192Ir‐based afterloading brachytherapy at this time, this report establishes a general framework that can easily be extended to other brachytherapy MBDCAs and brachytherapy sources. The AAPM, ESTRO, ABG, and ABS recommend that clinical medical physicists implement the workflow presented in this report to validate both the basic and the advanced dose calculation features of their commercial MBDCAs. Recommendations are also given to vendors to integrate advanced analysis tools into their brachytherapy treatment planning system to facilitate extensive dose comparisons. The use of the test cases for research and educational purposes is further encouraged.

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Monte Carlo dosimetry study of novel rotating MRI-compatible shielded tandems for intensity modulated cervix brachytherapy

Cited by 11 publications

References 28 publications

A novel minimally invasive dynamic‐shield, intensity‐modulated brachytherapy system for the treatment of cervical cancer

A novel minimally invasive dynamic‐shield, intensity‐modulated brachytherapy system for the treatment of cervical cancer

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

AAPM WGDCAB Report 372: A joint AAPM, ESTRO, ABG, and ABS report on commissioning of model‐based dose calculation algorithms in brachytherapy

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