基于危及器官分区约束的等效均匀剂量优化在直肠癌容积调强放疗中的应用

摘要

目的:评估基于危及器官分区约束的等效均匀剂量优化在直肠癌容积调强放疗中的剂量学和生物学优势.方法:随机选取临床批准的经过剂量-体积优化的直肠癌容积调强放疗计划10例(PHY计划).以PHY计划为基础,分别根据小肠,膀胱与靶区的位置关系,将危及器官进行分区并根据组织特性参数(a值)对剂量热点敏感性的不同,给予不同的a值进行等效均匀剂量优化(EUD计划).根据a值越大对剂量热点越敏感这一特点,靶区与危及器官重叠部分的剂量相对其它区域来说较高,热点出现概率较大,取较大的a值进行等效均匀剂量优化(a=10).重叠部分外扩9 mm且与小肠和膀胱相交区域的剂量热点出现概率相对重叠区域较低,a值取8和5;同理,其余小肠和膀胱区域由于远离高剂量的靶区,a值分别取6.7和2.3.最后对EUD计划和PHY计划的剂量学以及生物学进行比较,并且通过SPSS 22软件对所得数据的差异性进行分析.结果:EUD计划的靶区情况与PHY计划基本一致.进行分区处理的EUD计划中危及器官的剂量参数和正常组织并发症概率均有不同程度降低,其数据差异均具有统计学意义(P<0.05).其中,小肠和膀胱的平均剂量分别下降4.5、6.8 Gy;正常组织并发症概率下降40.0％和6.6％.结论:基于危及器官分区约束的等效均匀剂量优化在直肠癌容积调强放疗中能够在保持靶区不受影响的情况下显著降低危及器官的受照剂量以及放疗并发症概率,对改善计划质量具有一定意义.%Objective To evaluate the dosimetric and biological advantages of equivalent uniform dose optimization based on organs-at-risk (OAR) partition constraint in volumetric modulated arc therapy (VMAT) for rectal cancer. Methods With dose-volume constraints, 10 VMAT plans for rectal cancer which were approved in clinic were selected (PHY plans). Based on the PHY plans, we performed the OAR partition according to the position relationships among the small intestine, the bladder and target areas, and carried out the equivalent uniform dose (EUD) optimization by giving different specific-tissues parameters (a value) which were different in sensitivity to hot spots, finally obtaining EUD plans. The greater a value was more sensitive to hot spots, and the dose of overlaps between target areas and OAR was relatively higher than that of other regions, with a higher probability of occurrence of hot spots, thus we selected a larger a value (a=10) to perform EUD optimization. The area where 9 mm expanded from the overlapping portions was intersected with the small intestine and the bladder had a low incidence of hot spots, therefore a value was at 8 and 5. As the rest of small intestine and bladder were away from high-dose area, we took a value of 6.7 and 2.3. The dosimetric and biological features of EUD plans and PHY plans were compared and SPSS 22 software was used to analyze the obtained data. Results The differences between PHY plan and EUD plan in PTV parameters were trivial. However, compared with PHY plans, EUD plans had reduced OAR dose parameters and normal tissue complication probability, with statistically significant differences (P<0.05). In EUD plan, the mean dose of the small intestine and the bladder decreased by 4.5 and 6.8 Gy, respectively;NTCP decreased 40.0％and 6.6％, respectively. Conclusion EUD optimization based on OAR partition constraint in VMAT for rectal cancer obviously decreases the OAR irradiation dose and normal tissue complication probability, without affecting PTV, which is significant to improve the quality of the plan.