食管癌放射治疗中自适应放疗计划时机选择的研究

Exploration of timing of modifying adaptive radiotherapy plan for esophageal cancer

目的分析食管癌放疗过程中靶体积变化对剂量分布的影响,为选择修改放疗计划时机提供参考。方法选取30例食管癌放疗病例,首周每天1次以及后续第6、9、11、14、16、19、21次治疗前采集患者影像,记录首周摆位误差,计算新的靶区外扩边界值并制定新计划,评估靶体积变化及靶区剂量D_(95%)。根据放疗过程中靶体积变化情况选择修改放疗计划时机,将修改计划前、后的实际剂量进行累加,并与原计划比较。结果新的外扩边界值为LR:0.47cm、AP:0.47cm、CC:0.84cm,生成新的靶区体积小于初始靶体积(P<0.05)。新计划靶区剂量D95%与原计划比较差异无统计学意义(P>0.05)。放疗过程中靶体积发生了不同程度的退缩,且在第11至第14次治疗期间退缩最快,退缩率达到5.5%。在第11次治疗后修改计划,修改后的累加计划中双肺V_(5)、V_(10)、V_(20)、V_(30)、D_(mean),心脏V_(30)、V_(40),以及脊髓D_(max)的受照剂量均有降低(P<0.05),靶区剂量D_(95%)与原计划无差异(P>0.05)。结论使用首周摆位误差计算新的外扩边界值小于常规外扩边界值,但不影响靶区剂量分布。在靶区退缩率最大时制定的自适应计划,进一步降低了正常组织受量,不影响靶区剂量分布。建议在第11次治疗后修改放疗计划。

Objective The influence on dose distribution due to target volume change during radiotherapy for esophageal cancer was analyzed to select the right time to modify the radiotherapy plan.Methods Thirty cases of esophageal cancer undergoing radiotherapy were selected.Images of the patients were collected daily during the first week and before the 6th,9th,11th,14th,16th,19th,and 21st treatment sessions.The new margins of the target area were calculated according to the mean value of the positioning errors which were recorded during the first week.A new plan was created using the newly calculated target margin to evaluate target volume change and its impact on target dose coverage D_(95%).Based on the changes in target volume observed during the radiotherapy process,the timing for modifying the radiotherapy plan was determined.The actual doses before and after the modification were summed and compared with the dose distribution according to the original plan.Results The expanded margins values calculated by the positioning error were LR:0.47cm、AP:0.47cm、CC:0.84cm.The volume of the target area generated using the newly expanded margins was significantly smaller than the initial target area(P<0.05).However,the target dose coverage D_(95% )of the new plan did not dif fer statistically compared to the original plan(P >0.05).As radiotherapy progressed,the target volume experienced varying degrees of shrinkage,with the most rapid change occurring between the 11th and 14th treatments,where a shrinkage rate of 5.5% was observed.The radiotherapy plan was modified after the 11th treatment,resulting in a statistically significant reduction in the cumulative dose to the V_5、V_(10)、V_(20)、V_(30)、D_(mean) of lungs,V_(30)、V_(40 )of heart and D_(max) of spinalcord in the revised plan(P < 0.05).However,there was no statistically significant difference in the target dose coverage D_(95) between the modified cumulative plan and the original plan(P >0.05).Conclusion The new external margins value are smaller than the conventional external margins value and the new radiotherapy plan developed based on positioning errors observed during the first week didn't compromise the dose distribution to the target.An adaptive plan was developed when the target receding rate reaches its maximum,and that can further decrease the dose to normal tissues without af fecting target dose distribution.It is advisable to revise the radiotherapy plan after the 11th fraction.