Study of out‐of‐field dose in photon radiotherapy: A commercial treatment planning system versus measurements and Monte Carlo simulations

Sánchez‐Nieto, B.; Medina‐Ascanio, K. N.; Rodriguez-Mongua, J.L.; Doerner, Edgardo; Espinoza, Ignacio

doi:10.1002/mp.14356

Cited by 33 publications

(37 citation statements)

References 25 publications

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“…During irradiations at different sites, the measured dose at check points far from the treatment field was extremely small (less than 0.5 cGy), resulting in a very large D TPS /D OSLD . In this study, the underestimation of out-of-field dose calculation of Monaco TPS within 2 % and 5 % isodose ranges is similar to the experimental results presented by Sánchez-Nieto et al 44 . The overestimation at 0 -2 % isodose area became more severe with increasing distance from the beam The results of this study were specific to the Monaco TPS version 5.40.01 and Varian…”

Section: Accepted Articlesupporting

confidence: 91%

Out‐of‐field dose assessment for a 1.5 T MR‐Linac with optically stimulated luminescence dosimeters

et al. 2021

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To assess the out-of-field surface and internal dose of the 1.5T MR-Linac compared to the conventional external beam linac using optically stimulated luminescence dosimeters (OSLDs), and evaluate the out-of-field dose calculation accuracy of the Monaco treatment planning system of the 1.5T MR-Linac. Methods: A cubic solid water phantom, with OSLDs on the surface, was vertically irradiated by MR-Linac square fields with different sizes. In addition, OSLDs were arranged out of the beam edges in four directions. An anthropomorphic adult phantom, with 125 cm 3 simulated volume, was irradiated in 4 orthogonal directions by both MR-Linac and conventional linac at the head, thoracic, and pelvic sites. Out-of-field doses were measured by OSLDs on both the surface and internal emulational organs at risk (OARs). The results were compared to the simulated dose from Monaco treatment planning system (TPS). Results: At different field sizes (5 × 5 to 20 × 20 cm 2) and distances (1 to 10 cm) to beam edge, the out-of-field surface dose measured on MR-Linac varied from 0.16 % (10 cm to 5 × 5 cm 2 edge) to 7.02 % (1 cm to 20 × 20 cm 2 edge) of the maximum dose laterally and from 0.14 % (10 cm to 5 × 5 cm 2 edge) to 8.56 % (1 cm to 20 × 20 cm 2 edge) of the maximum dose longitudinally. Compared to the OSLDs measured data, the Monaco TPS presented an overestimate of the out-of-field dose of OARs at 0-2 % isodose area on both surface and internal check points, and the overestimation gets greater as the distance increases. The underestimation was found to be 0-35% at 2%-5% Accepted Article This article is protected by copyright. All rights reserved isodose area on both surface and internal check points. Compared to the conventional linac, MR-Linac delivered higher average values of out-of-field dose on surface check points (20 %, 19 %, 21 %) and internal simulated OARs (42 %, 37 %, 9 %) of the anthropomorphic phantom at head, thoracic and pelvic irradiations, respectively. Conclusions: Compared to the conventional linac, MR-Linac has the same out-of-field dose distribution. However, considering the absolute dose values, MR-Linac delivered relatively higher out-of-field doses on both surface and internal OARs. Additional radiation shielding to patients undergoing MR-Linac may provide protection from out-of-field exposure.

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Section: Accepted Articlesupporting

confidence: 91%

Out‐of‐field dose assessment for a 1.5 T MR‐Linac with optically stimulated luminescence dosimeters

et al. 2021

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“…Also for a 6 MV beam, Sánchez‐Nieto et al 22 used TLD‐100 to measure the out‐of‐field dose imparted by a 10 × 10 cm 2 field at 5 cm deep in a water phantom, at distances 1–7 cm from the field edge, to be in the range 1.4%–7.7% of the dose imparted at isocenter. Our measurements, as shown in Figure 4(a) together with theirs, show excellent qualitative and quantitative agreement.…”

Section: Discussionmentioning

confidence: 99%

Out‐of‐field mean photon energy and dose from 6 MV and 6 MV FFF beams measured with TLD‐300 and TLD‐100 dosimeters

et al. 2021

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To measure the out-of -field mean photon energy and dose imparted by the secondary radiation field generated by 6 MV and 6 MV FFF beams using TLD-300 and TLD-100 dosimeters and to use the technique to quantify the contributions from the different sources that generate out-of -field radiation. Methods: The mean photon energy and the dose were measured using the TLD-300 glow curve properties and the TLD-100 response, respectively. The TLD-300 glow curve shape was energy-calibrated with gamma rays from 99m Tc, 18 F, 137 Cs, and 60 Co sources, and its energy dependence was quantified by a parameter obtained from the curve deconvolution. The TLD-100 signal was calibrated in absorbed dose-to-water inside the primary field. Dosimeters were placed on the linac head, and on the surface and at 4.5 cm depth in PMMA at 1-15 cm lateral distances from a 10 × 10 cm 2 field edge at the isocenter plane. Three configurations of dosimeters around the linac were defined to identify and quantify the contributions from the different sources of out-of -field radiation. Results: Typical energies of head leakage were about 500 keV for both beams. The mean energy of collimator-scattered radiation was equal to or larger than 1250 keV and, for phantom-scattered radiation, mean photon energies were 400 keV for the 6 MV and 300 keV for the 6 MV FFF beam. Relative uncertainties to determine mean photon energy were better than 15% for energies below 700 keV, and 40% above 1000 keV. The technique lost its sensitivity to the incident photon energy above 1250 keV. On the phantom surface and at 1-15 cm from the field edge, 80%-90% of out-of -field dose came from scattering in the secondary collimator. At 4.5 cm deep in the phantom and 1-5 cm from the field edge, 50%-60% of the out-of -field dose originated in the phantom. At the points of measurement, the head leakage imparted less than 0.1% of the dose at the isocenter. The 6 MV FFF beam imparted 8-36% less out-of -field dose than the 6 MV beam. These energy results are consistent with general Monte Carlo simulation predictions and show excellent agreement with simulations for a similar linac. The measured out-of -field doses showed good agreement with independent evaluations. Conclusions: The out-of -field mean photon energy and dose imparted by the secondary radiation field were quantified by the applied TLD-300/TLD-100 method. The main sources of out-of -field dose were identified and quantified using three configurations of dosimeters around the linac. This technique could be of value to validate Monte Carlo simulations where the linac head design, configuration, or material composition are unavailable.

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“…Given that treatments only imply exposure to photons, equivalent dose equals absorbed dose, which could be extracted from TPS data. However, the accuracy of TPS outside the border of the field has been questioned [17,18]. Consequently, in this work the Dose Volume Histogram (DVH) information provided by the TPS was only used to determine the mean absorbed dose administered to organs inside the 5% isodose (i.e., approximately up to 3-4 cm of the border of the field).…”

Section: Dosimetrymentioning

confidence: 99%

Low dose radiation therapy for COVID-19: Effective dose and estimation of cancer risk

Garcia-Hernandez

Romero-Expósito

Sánchez‐Nieto

2020

Radiotherapy and Oncology

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Background and purpose The objective of this work is to evaluate the risk of carcinogenesis of low dose ionizing radiation therapy (LDRT), for treatment of immune-related pneumonia following COVID-19 infection, through the estimation of effective dose and the lifetime attributable risk of cancer (LAR). Material and methods LDRT treatment was planned in male and female computational phantoms. Equivalent doses in organs were estimated using both treatment planning system calculations and a peripheral dose model (based on ionization chamber measurements). Skin dose was estimated using radiochromic films. Later, effective dose and LAR were calculated following radiation protection procedures. Results Equivalent doses to organs per unit of prescription dose range from 10 mSv/cGy to 0.0051 mSv/cGy. Effective doses range from 204 mSv to 426 mSv, for prescription doses ranging from 50cGy to 100cGy. Total LAR for a prescription dose of 50 cGy ranges from 1.7 to 0.29 % for male and from 4.9 to 0.54 % for female, for ages ranging from 20 to 80 years old. Conclusions The organs that mainly contribute to risk are lung and breast. Risk for out-of-field organs is low, less than 0.06 cases per 10000. Female LAR is on average 2.2 times that of a male of the same age. Effective doses are of the same order of magnitude than higher dose interventional radiology techniques. For a 60 year-old male, LAR is 8 times that from a cardiac CT, when prescription dose is 50 cGy.

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Study of out‐of‐field dose in photon radiotherapy: A commercial treatment planning system versus measurements and Monte Carlo simulations

Cited by 33 publications

References 25 publications

Out‐of‐field dose assessment for a 1.5 T MR‐Linac with optically stimulated luminescence dosimeters

Out‐of‐field dose assessment for a 1.5 T MR‐Linac with optically stimulated luminescence dosimeters

Out‐of‐field mean photon energy and dose from 6 MV and 6 MV FFF beams measured with TLD‐300 and TLD‐100 dosimeters

Low dose radiation therapy for COVID-19: Effective dose and estimation of cancer risk

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