Part II: Verification of the TrueBeam head shielding model in Varian VirtuaLinac via out‐of‐field doses

Wijesooriya, K.; Liyanage, N.; Kaluarachchi, Maduka; Sawkey, D

doi:10.1002/mp.13263

Cited by 10 publications

(14 citation statements)

References 30 publications

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“…Leakage dose at 100 cm away from primary beam was <0.1% of the CAX dose, thus meeting the acceptance criteria specified by AAPM TG 45 . The comparison of these measurements to TrueBeam head shielding model‐based Monte Carlo simulations from Varian VirtuaLinac will be published separately …”

Section: Discussionmentioning

confidence: 88%

“…34 The comparison of these measurements to TrueBeam head shielding model-based Monte Carlo simulations from Varian VirtuaLinac will be published separately. 35 Kry et al 23 reported in-plane measurements for 6X beams for Varian C-series linac dose for 4 9 4 cm 2 , 10 9 10 cm 2 , and 20 9 20 cm 2 out to a distance of 55 cm from CAX are given in Fig. 2 of their paper.…”

Section: Discussionmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 88%

Section: Discussionmentioning

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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“…Similarly, in a study using Monte Carlo simulations, Wijesooriya, et al reported that out-of-field doses reduced exponentially with distance. 19 Overall, these results demonstrate the feasibility of using OSLDs for low-scattered radiation measurements.…”

Section: Discussionmentioning

confidence: 56%

Effect of protective glasses on radiation dose to eye lenses during whole breast irradiation

Nakamura

Suzuki

Kato

et al. 2020

J Applied Clin Med Phys

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Objectives The efficacy of radiotherapy for breast cancer has greatly improved owing to better irradiation methods. Radiotherapy aims to deliver therapeutic doses to predetermined target volumes while sparing surrounding healthy tissues. However, there are few reports on radiation exposure to eye lenses, and the recommended exposure limits to ocular lens have been substantially reduced in recent years. This study aimed to investigate the amount of radiation exposure to eye lenses using optically stimulated luminescence dosimeters (OSLDs) and determine whether wearing special protective devices to protect the eyes, as an organ at risk, during whole breast irradiation, is necessary. Methods This experiment used OSLDs on water‐equivalent phantom to measure the change in scattered radiation dose due to the difference of irradiation field while using 4‐ and 6‐MV photons of TrueBeam linear accelerator. Using a total treatment dose of 50 Gy, a target was positioned to approximate the breast, and a plan was formulated to deliver 2 Gy per treatment by tangential irradiation. The mean (SD) irradiation dose at the lens position outside the irradiation field was reported. Results The scattered radiation dose outside the irradiation field was more affected by the irradiation field size than by the radiation energy. The out‐of‐field irradiation dose with a larger field of view was higher than that with a smaller field of view. The use of 0.07‐ and 0.83‐mm‐thick lead shield protective glasses reduced the radiation dose by 56.1% (P < .001) and 55.6% (P < .001), respectively. Conclusions In this experimental model, the amount of radiation the eye was exposed to during whole breast irradiation was determined by the distance of the eye from the radiation field edge and by wearing protective glasses. In clinical practice, the protection offered by eyeglasses may reduce the risk of long‐term side effects and allow the use of higher intensive radiotherapy.

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“…2 Outof -field MC simulations should be validated through measurements. 2,11 Recent investigations by our group 12 have reported a remarkable sensitivity of the glow curve of the TLD material CaF 2 :Tm, called TLD-300, to photon energy in the range encountered in diagnostic radiology applications. Previously, this feature had been mostly studied as a function of the radiation quality of ion beams.…”

Section: Introductionmentioning

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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Part II: Verification of the TrueBeam head shielding model in Varian VirtuaLinac via out‐of‐field doses

Cited by 10 publications

References 30 publications

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

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

Effect of protective glasses on radiation dose to eye lenses during whole breast irradiation

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

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