Department of Physics and Astronomy, Louisiana State University and Agricultural and Mechanical College, Baton Rouge, LA, USA.
Department of Physics, Mary Bird Perkins Cancer Center, Baton Rouge, LA, USA.
Radiat Oncol. 2021 Dec 7;16(1):234. doi: 10.1186/s13014-021-01956-6.
No consensus currently exists about the correct margin size to use for spinal SBRT. Margins have been proposed to account for various errors individually, but not with all errors combined to result in a single margin value. The purpose of this work was to determine a setup margin for five-fraction spinal SBRT based on known errors during radiotherapy to achieve at least 90% coverage of the clinical target volume with the prescription dose for at least 90% of patients and not exceed a 30 Gy point dose or 23 Gy to 10% of the spinal cord subvolume.
The random and systematic error components of intrafraction motion, residual setup error, and end-to-end system accuracy were measured. The patient's surface displacement was measured to quantify intrafraction motion, the residual setup error was quantified by re-registering accepted daily cone beam computed tomography setup images, and the displacement between measured and planned dose profiles in a phantom quantified the end-to-end system accuracy. These errors and parameters were used to identify the minimum acceptable margin size. The margin recommendation was validated by assessing dose delivery across 140 simulated patient plans suffering from various random shifts representative of the measured errors.
The errors were quantified in three dimensions and the analytical margin generated was 2.4 mm. With this margin applied in the superior/inferior direction only, at least 90% of the CTV was covered with the prescription dose for 96% of the 140 patients simulated with minimal negative effect on the spinal cord dose levels.
The findings of this work support that a 2.4 mm margin applied in the superior/inferior direction can achieve at least 90% coverage of the CTV for at least 90% of dual-arc volumetric modulated arc therapy spinal SBRT patients in the presence of errors when immobilized with vacuum bags.
目前对于脊柱 SBRT 应使用的正确边缘大小尚无共识。边缘大小已被提议用于单独考虑各种误差，但并未将所有误差组合起来以得出单个边缘值。这项工作的目的是确定五部分分割脊柱 SBRT 的设置边缘，以根据放射治疗期间的已知误差来实现临床靶体积至少 90%的处方剂量覆盖，并且不超过 30Gy 点剂量或 23Gy 至脊髓亚体积的 10%。
测量分次内运动、残余设置误差和端到端系统精度的随机和系统误差分量。通过测量患者表面位移来量化分次内运动，通过重新注册可接受的每日锥形束计算机断层扫描设置图像来量化残余设置误差，通过在体模中测量和计划剂量分布之间的位移来量化端到端系统精度。这些误差和参数用于确定最小可接受的边缘大小。通过评估 140 个模拟患者计划的剂量传递来验证边缘推荐，这些计划受到代表测量误差的各种随机移位的影响。
在三个维度上量化了误差，并生成了 2.4mm 的分析边缘。仅在上下方向应用此边缘，至少 90%的 CTV 被处方剂量覆盖，对于模拟的 140 个患者中的 96%，对脊髓剂量水平的负面影响最小。
这项工作的结果支持在使用真空袋固定时，对于使用双弧容积调强弧形治疗的脊柱 SBRT 患者，2.4mm 的边缘仅在上下方向应用可以实现至少 90%的 CTV 覆盖，同时存在误差时至少 90%的患者可以达到。
