Lin Teh, Hossain Murshed, Fan Jiajin, Ma C-M Charlie
Department of Radiation Oncology, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA.
Department of Radiation Oncology, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA.
Med Dosim. 2018;43(4):334-343. doi: 10.1016/j.meddos.2017.11.003. Epub 2017 Dec 26.
When a linear accelerator is unavailable for treatment, a clinical decision is imminent regarding whether a patient should be treated on a linear accelerator other than the machine the patient was scheduled on, or whether treatment should be postponed until the original Linac becomes available. This work investigates the feasibility of switching patients to different accelerators for intensity-modulated radiation therapy (IMRT). We have performed Monte Carlo simulations of photon beams from different Linac models and vendors. Prostate and head and neck (H&N) treatment plans for Siemens Primus, Primart, and Varian 21EX accelerators are studied in this work. Dose distributions for given plans are recalculated using different beam data with the same nominal energy from different Linacs. We have compared dose-volume histograms (DVHs) and the maximum, the minimum, and the mean doses to the target and critical structures because of switching accelerators. In the process of switching a treatment plan to a different accelerator, issues exist, including optimum penumbra compensation, dose distribution at the boundary of target and critical structures, and multileaf collimator (MLC) leaf-width effects, which need to be considered and verified with measurements. Our Monte Carlo simulation results confirm that, for the cases we tested, the dose received by 95% of the planning target volume differs by 0.2% to 1.5% between Siemens Primus and Varian 21EX Linacs. The discrepancy is within our clinical acceptance criteria of 3% for IMRT treatments. In making the final decision on whether to switch machines or not, the tumor control probabilities (TCPs) based on a linear-quadratic model are compared. Based on the analyses performed in this work, it is therapeutically more beneficial to switch a patient to a different machine than to postpone a treatment until the original machine is available, especially for fast-growing tumors such as H&N cancers.
当无法使用直线加速器进行治疗时，关于患者是否应在其原定计划使用的直线加速器以外的其他直线加速器上接受治疗，或者治疗是否应推迟到原直线加速器可用，临床决策迫在眉睫。这项工作研究了将患者转换到不同加速器进行调强放射治疗（IMRT）的可行性。我们对来自不同直线加速器型号和供应商的光子束进行了蒙特卡罗模拟。本研究针对西门子Primus、Primart和瓦里安21EX加速器的前列腺及头颈部（H&N）治疗计划展开。使用来自不同直线加速器的具有相同标称能量的不同束流数据，对给定计划的剂量分布进行重新计算。我们比较了由于更换加速器导致的靶区和危及器官的剂量体积直方图（DVH）以及最大、最小和平均剂量。在将治疗计划转换到不同加速器的过程中，存在一些问题，包括最佳半值层补偿、靶区和危及器官边界处的剂量分布以及多叶准直器（MLC）叶片宽度效应，这些都需要通过测量进行考虑和验证。我们的蒙特卡罗模拟结果证实，对于我们测试的病例，西门子Primus直线加速器和瓦里安21EX直线加速器之间，95%的计划靶区体积所接受的剂量相差0.2%至1.5%。这种差异在我们IMRT治疗3%的临床可接受标准范围内。在就是否更换机器做出最终决策时，会比较基于线性二次模型的肿瘤控制概率（TCP）。基于本研究的分析，将患者转换到不同机器进行治疗比推迟治疗直到原机器可用在治疗上更有益，特别是对于像H&N癌症这样生长迅速的肿瘤。
