Australian Clinical Dosimetry Service, Australian Radiation Protection and Nuclear Safety Agency, Melbourne, Australia; School of Health and Biomedical Sciences, RMIT University, Melbourne, Australia.
Australian Clinical Dosimetry Service, Australian Radiation Protection and Nuclear Safety Agency, Melbourne, Australia; Olivia Newton John Cancer Wellness Centre, Melbourne, Australia.
Phys Med. 2021 Apr;84:265-273. doi: 10.1016/j.ejmp.2021.03.011. Epub 2021 Mar 25.
Current quality assurance of radiotherapy involving bony regions generally utilises homogeneous phantoms and dose calculations, ignoring the challenges of heterogeneities with dosimetry problems likely occurring around bone. Anthropomorphic phantoms with synthetic bony materials enable realistic end-to-end testing in clinical scenarios. This work reports on measurements and calculated corrections required to directly report dose in bony materials in the context of comprehensive end-to-end dosimetry audit measurements (63 plans, 6 planning systems).
Radiochromic film and microDiamond measurements were performed in an anthropomorphic spine phantom containing bone equivalent materials. Medium dependent correction factors, k, were established using 6 MV and 10 MV Linear Accelerator Monte Carlo simulations to account for the detectors being calibrated in water, but measuring in regions of bony material. Both cortical and trabecular bony material were investigated for verification of dose calculations in dose-to-medium (D) and dose-to-water (D) scenarios.
For D calculations, modelled correction factors for cortical and trabecular bone in film measurements, and for trabecular bone in microDiamond measurements were 0.875(±0.1%), 0.953(±0.3%) and 0.962(±0.4%), respectively. For D calculations, the corrections were 0.920(±0.1%), 0.982(±0.3%) and 0.993(±0.4%), respectively. In the audit, application of the correction factors improves the mean agreement between treatment plans and measured microDiamond dose from -2.4%(±3.9%) to 0.4%(±3.7%).
Monte Carlo simulations provide a method for correcting the dose measured in bony materials allowing more accurate comparison with treatment planning system doses. In verification measurements, algorithm specific correction factors should be applied to account for variations in bony material for calculations based on D and D.
目前涉及骨骼区域的放射治疗质量保证通常利用均匀体模和剂量计算，忽略了骨骼周围可能出现的剂量学问题的不均匀性挑战。具有合成骨材料的人体模型能够在临床情况下实现端到端的逼真测试。本工作报告了在全面端到端剂量审核测量（63 个计划，6 个计划系统）的背景下，直接在骨材料中报告剂量所需的测量和计算校正。
在包含骨等效材料的人体脊柱模型中进行了光致变色胶片和微金刚石测量。使用 6MV 和 10MV 线性加速器蒙特卡罗模拟建立了介质相关校正因子 k，以补偿探测器在水中校准但在骨材料区域测量的情况。研究了皮质骨和松质骨材料，以验证剂量到介质（D）和剂量到水（D）情况下的剂量计算。
对于 D 计算，在胶片测量中，皮质骨和松质骨以及微金刚石测量中的松质骨的模型校正因子分别为 0.875(±0.1%)、0.953(±0.3%)和 0.962(±0.4%)。对于 D 计算，校正因子分别为 0.920(±0.1%)、0.982(±0.3%)和 0.993(±0.4%)。在审核中，应用校正因子将治疗计划与微金刚石测量剂量之间的平均一致性从-2.4%(±3.9%)提高到 0.4%(±3.7%)。
蒙特卡罗模拟为校正骨材料中测量的剂量提供了一种方法，允许更准确地与治疗计划系统剂量进行比较。在验证测量中，应根据 D 和 D 计算应用算法特定的校正因子来考虑骨材料的变化。
