Field size dependent mapping of medical linear accelerator radiation leakage

Bezin, Julien; Veres, A.; Lefkopoulos, Dimitri; Chavaudra, J.; Deutsch, Éric; Vathaire, Florent de; Diallo, Ibrahima

doi:10.1088/0031-9155/60/5/2103

Cited by 12 publications

(19 citation statements)

References 32 publications

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“…Discrepancies between calculations and measurements were found to be about 10%. In a similar manner, VũBezin et al [78] found discrepancies between leakage measurements and calculations to be below 7% for points within 100 cm of the central beam axis.…”

Section: Estimation Of the Dose At The Point Or Volume Of Interestmentioning

confidence: 65%

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A review of uncertainties in radiotherapy dose reconstruction and their impacts on dose–response relationships

et al. 2017

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Proper understanding of the risk of radiation-induced late effects for patients receiving external photon beam radiotherapy requires the determination of reliable dose–response relationships. Although significant efforts have been devoted to improving dose estimates for the study of late effects, the most often questioned explanatory variable is still the dose. In this work, based on a literature review, we provide an in-depth description of the radiotherapy dose reconstruction process for the study of late effects. In particular, we focus on the identification of the main sources of dose uncertainty involved in this process and summarise their impacts on the dose–response relationship for radiotherapy late effects. We provide a number of recommendations for making progress in estimating the uncertainties in current studies of radiotherapy late effects and reducing these uncertainties in future studies.

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Section: Estimation Of the Dose At The Point Or Volume Of Interestmentioning

confidence: 65%

“…This has led medical physicists to develop in-house algorithms for estimating out-of-field doses. Three main categories of out-of-field dose algorithms exist: measurement-based algorithms [6, 14-16, 72, 76, 77], multi-source algorithms [17,78] and Monte Carlo (MC) algorithms [44,79,80].…”

Section: Estimation Of the Dose At The Point Or Volume Of Interestmentioning

confidence: 99%

A review of uncertainties in radiotherapy dose reconstruction and their impacts on dose–response relationships

et al. 2017

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“…Analytical models, on the other hand, are comparatively simple, fast, and free of statistical fluctuations. There is also promising evidence suggesting they can be dosimetrically accurate in the out‐of‐field region . Further, a recently published analytical model is readily generalizable to different treatment machines and irradiation conditions without the need for proprietary information due to its physics‐based framework .…”

Section: Introductionmentioning

confidence: 99%

Method to quickly and accurately calculate absorbed dose from therapeutic and stray photon exposures throughout the entire body in individual patients

et al. 2020

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Purpose: Photon radiotherapy techniques typically devote considerable attention to limiting the exposure of healthy tissues outside of the target volume. Numerous studies have shown, however, that commercial treatment planning systems (TPSs) significantly underestimate the absorbed dose outside of the treatment field. The purpose of this study was to test the feasibility of quickly and accurately calculating the total absorbed dose to the whole body from photon radiotherapy in individual patients. Methods: We created an extended TPS by implementing a physics-based analytical model for the absorbed dose from stray photons during photon therapy into a research TPS. We configured and validated the extended TPS using measurements of 6-and 15-MV photon beams in water-box and anthropomorphic phantoms. We characterized the additional computation time required for therapeutic and stray dose calculations in a 44 9 30 9 180 cm 3 water-box phantom. Results: The extended TPS achieved superior dosimetric accuracy compared to the research TPS in both water and anthropomorphic phantoms, especially outside of the primary treatment field. In the anthropomorphic phantom, the extended TPS increased the generalized gamma index passing rate by a factor of 10 and decreased the median dosimetric discrepancy in the out-of-field region by a factor of 26. The extended TPS achieved an average discrepancy <1% in and near the treatment field and <1 mGy/Gy far from the treatment field in the anthropomorphic phantom. Characterization of computation time revealed that on average, the extended TPS only required 7% longer than the research TPS to calculate the total absorbed dose. Conclusions: The results of this work suggest that it is feasible to quickly and accurately calculate whole-body doses inside and outside of the therapeutic treatment field in individual patients on a routine basis using physics-based analytical dose models. This additional capability enables a more personalized approach to minimizing the risk of radiogenic late effects, such as second cancer and cardiac toxicity, as part of the treatment planning process.

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“…Out-of-field dose is an unintended consequence of radiation therapy that may increase the risk of late effects such as myocardial damage [1][2][3][4][5] and secondary cancers. [6][7][8] Out-of-field dose consists of three main components: head leakage, 9,10 internal scatter, 11 and collimator scatter. Unlike internal scatter which is an unavoidable radiation dose, head leakage can and should be minimized.…”

Section: Introductionmentioning

confidence: 99%

Part I: Out‐of‐field dose mapping for 6X and 6X‐flattening‐filter‐free beams on the TrueBeam for extended distances

Wijesooriya

2019

Medical Physics

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Purpose With increasing cancer treatment success rates, many patients go on to live long, productive lives following recovery. Therefore, minimizing potential side effects due to dose outside the treated field is becoming a significant consideration in radiation therapy. With many potential treatment configurations available, it is important to quantify how out‐of‐field dose varies with common variables such as distance from isocenter, couch angle, jaw size, and flattening‐filter setting. The accurate quantification of out‐of‐field dose at extended distances could also benefit researchers and detector developers. While data exist for out‐of‐field dose from older linear accelerator (Linac) models, the phenomenon has not been described for the latest generation of machines, such as the Varian TrueBeam. The purpose of this study was to comprehensively quantify out‐of‐field dose for the Varian TrueBeam Linac low energy photons in a wide range of positions and treatment geometries. Method and Materials Out‐of‐field doses were measured using two phantom setups: (a) A large volume ion chamber with a buildup sleeve to quantify head leakage and collimator scatter background dose; and (b) A farmer ion chamber in solid water to incorporate phantom scatter in addition to collimator scatter, and head leakage background dose. In both cases, the ion chamber was positioned with its length along the slowly varying transverse direction (perpendicular to the radial from isocenter). Doses were measured for four symmetric jaw settings (2 × 2 cm2, 4 × 4 cm2, 10 × 10 cm2, and 20 × 20 cm2) for a range of distances from the isocenter (0–100 cm). The angular dependence of the out‐of‐field dose was measured using four different angles: 0°, 45°, 90°, and 135° with respect to the in‐plane direction. All measurements were performed for both 6X and 6X‐flattening‐filter‐free (FFF) beams. Results The lowest out‐of‐field doses were observed at 60 cm away from isocenter in both in‐plane and cross‐plane directions for fields smaller than 10 × 10 cm2. Out‐of‐field dose decreased with decreasing jaw size (a factor of 4.7 for 6X‐FFF and a factor of 3.1 for 6X going from 20 × 20 cm2 to 2 × 2 cm2 at 60 cm from isocenter in the in‐plane direction). The 6X‐FFF beam produced out‐of‐field doses as low as 64% of the 6X beam. Conclusion This study presents a comprehensive description of 6X and 6X‐FFF out‐of‐field doses on a Varian TrueBeam Linac including measurements at a range of positions, angles, and jaw settings and with and without phantom scatter.

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Field size dependent mapping of medical linear accelerator radiation leakage

Cited by 12 publications

References 32 publications

A review of uncertainties in radiotherapy dose reconstruction and their impacts on dose–response relationships

A review of uncertainties in radiotherapy dose reconstruction and their impacts on dose–response relationships

Method to quickly and accurately calculate absorbed dose from therapeutic and stray photon exposures throughout the entire body in individual patients

Part I: Out‐of‐field dose mapping for 6X and 6X‐flattening‐filter‐free beams on the TrueBeam for extended distances

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