Furuya Tomohisa, Phua Jun H, Ito Kei, Karasawa Katsuyuki
Department of Radiology, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, Tokyo 113-8677, Japan.
Department of Radiation Oncology, National Cancer Center Singapore, Singapore 169610, Singapore.
Med Dosim. 2019;44(4):415-420. doi: 10.1016/j.meddos.2019.03.002. Epub 2019 Mar 28.
The objective of the present study was to report whether the adequate spine stereotactic body radiotherapy (SBRT) plans were generated with feasible treatment duration for patients with large vertebral metastases undergoing re-irradiation. For 5 cases, the re-irradiation plans using static-field intensity-modulated radiation therapy (SIMRT), volumetric-modulated arc therapy (VMAT), and CyberKnife with a total prescribed dose (PD) of 24 Gy applied in 2 fractions were generated. A minimum dose to 95% of the evaluated planning target volume (PTV) that was >70% of PD (D > 70% PD) was defined as minimum criterion. For the dose tolerance of the spinal cord or thecal sac, which could affect the risk of radiation myelopathy, a volume-dose constraint of 12.2 Gy was set for the planning organ-at-risk volume of the spinal cord (PRV) or thecal sac and limited to 0.035 cc (D< 12.2 Gy) on the re-irradiation plans. For assessing the impact of the stricter dose constraint of PRV on the plan quality, we generated plans with a PRV dose constraint of D < 17.0 Gy, which was employed for patients with no previous history of radiation therapy (RT). Dose-volume histogram (DVH) analysis was performed for the PTV and spinal cord. Median PTV of all cases was 242.3 cc (range; 159.2 to 722.4 cc). Two out of 5 cases had a PTV >500 cc. The constraint of the PRV D was met in all re-irradiation plans; however, a comparison between the re-irradiation plan for patients with large vertebral metastases and the plan for cases with no RT history showed that the decrease of the target dose coverage was correlated with the stricter dose constraint of the PRV. For SIMRT and VMAT, the re-irradiation plans met the goal of the PTV D. On the other hand, CyberKnife plans could not achieve the constraints of the PTV D. This discrepancy is due to the constraint of treatment duration, which is defined as the comfortable duration for patients with large spinal metastases. Regardless of the delivery method used, treatment plan quality is impacted to a greater extent by the dose tolerance of the spinal cord than by the size of the tumor.
本研究的目的是报告对于接受再程放疗的大椎体转移瘤患者，是否能制定出合适的脊柱立体定向体部放疗（SBRT）计划并具有可行的治疗时长。针对5例患者，制定了采用静态野调强放疗（SIMRT）、容积调强弧形放疗（VMAT）和射波刀的再程放疗计划，总处方剂量（PD）为24 Gy，分2次给予。将评估的计划靶区（PTV）95%的最小剂量>70%PD（D>70%PD）定义为最低标准。对于可能影响放射性脊髓病风险的脊髓或硬脊膜囊的剂量耐受性，在再程放疗计划中为脊髓（PRV）或硬脊膜囊的计划危及器官体积设定了12.2 Gy的体积 - 剂量约束，并限制在0.035 cc（D<12.2 Gy）。为评估更严格的PRV剂量约束对计划质量的影响，我们制定了PRV剂量约束为D<17.0 Gy的计划，该约束用于既往无放疗（RT）史的患者。对PTV和脊髓进行了剂量体积直方图（DVH）分析。所有病例的PTV中位数为242.3 cc（范围：159.2至722.4 cc）。5例中有2例PTV>500 cc。所有再程放疗计划均满足PRV D的约束；然而，对大椎体转移瘤患者的再程放疗计划与无RT史病例的计划进行比较发现，靶区剂量覆盖的降低与更严格的PRV剂量约束相关。对于SIMRT和VMAT，再程放疗计划达到了PTV D的目标。另一方面，射波刀计划无法达到PTV D的约束。这种差异是由于治疗时长的约束，其被定义为大脊柱转移瘤患者的舒适时长。无论使用何种 delivery method（原文未明确，可能是“放疗方式”之类），治疗计划质量受脊髓剂量耐受性的影响程度大于受肿瘤大小的影响。
