Objective: To assess the potential dosimetric effects of arms movement in patients with Cyberknife spine tumors.
Methods: In the study, 12 patients with thoracic and lumbar tumors were retrospectively selected respectively. The contour of the patient's arms was sketched and the CT density was modified to be equivalent to air in order to simulate the extreme case when the arm was completely removed from the radiation fields. The dose of simulated plan was re-calculated with the original beam parameters and compared with the original plan. The changes of V100, D95, and D90, conformity index (CI) and heterogeneity index (HI) in planning target volume (PTV), as well as Dmax, D1cc and D2cc in the spinal cord, stomach, esophagus, and intestines were analyzed by comparing with the original plans.
Results: Compared with the original treatment plan, V100, D95, D90 and CI of PTV for the simulated plan was increased by 0.86%, 2.02%, 1.97% and 0.80% respectively, the difference was statistically significant (P < 0.05). Dmax, D1cc and D2cc of spinal cord was increased by 2.35%, 0.59% and 1.49% on average, compared with the original plan, the difference was statistically significant (P < 0.05). The difference was statistically significant only in average D2cc of stomach, which was increased by 1.70%, compared with the original plan (P < 0.05). There was no significant difference in dose change of eso-phagus and intestine between the original and simulated plans.
Conclusion: This study analyzed the most extreme arm position in spinal tumor of radiation therapy based on Cyberknife. It was found that the change of arm position had little effect on dosimetry. In addition, with the change of arm position, the dose in PTV and organ at risk (OAR) increased, but the increase was relatively small. Therefore, in some special cases where the patient really can't keep the arm position consistent during treatment, reasonable adjustment can be accepted. However, in order to ensure accurate radiotherapy, patient position should be as stable and consistent as possible.
目的: 评估患者手臂位置变化对射波刀脊柱肿瘤放射治疗潜在剂量学的影响。
方法: 选取胸椎与腰椎肿瘤患者各12例，勾画患者手臂轮廓并修改CT值和密度，使其等效为空气，模拟手臂完全移出射野的极端情况。保留原治疗计划的射束条件再次计算剂量，通过与原始计划的剂量体积直方图(dose-volume histogram, DVH)的参数比较，分析计划靶区(planning target volume, PTV)100%处方剂量的覆盖体积(V100)、95%PTV体积受照剂量(D95)、90%PTV体积受照剂量(D90)、适形指数(conformity index, CI)与异质性指数(heterogeneity index, HI)，以及脊髓、胃、食管、肠道的最大受照剂量(Dmax)、1cc体积(1 mL)受照剂量(D1cc)和2cc体积(2 mL)受照剂量(D2cc)的变化。
结果: 与原治疗计划相比，模拟计划的PTV V100、D95、D90、CI平均升高0.86%、2.02%、1.97%、0.80%，差异有统计学意义(P < 0.05);脊髓Dmax、D1cc与D2cc平均升高2.35%、2.59%、1.49%，差异有统计学意义(P < 0.05);胃D2cc平均升高1.70%，差异有统计学意义(P < 0.05);食管与肠道剂量差异无统计学意义。
结论: 在基于射波刀的脊柱肿瘤放射治疗过程中最极端的双臂位置情况下，发现手臂位置的改变对剂量学影响很小，并且随手臂位置的改变，靶区与危及器官(organ at risk, OAR)的剂量有所增加，但增幅相对较小，因此，在某些特殊情况下，患者确实无法始终保持手臂位置一致时，可以进行合理的调整，但是为了保证剂量的精确投照，应尽可能实现患者治疗体位的稳定性与一致性。
Keywords: Cyberknife; Dosimetry; Position of arm; Spinal tumor.