前列腺癌调强放疗的治疗方案比较

Comparison of seven intensity modulated radiation therapy plans for prostate cancer

目的通过对前列腺癌调强放疗的多种布野方案比较,确定符合临床要求的最佳方案。方法对8例前列腺癌患者采用调强放疗方案,处方总剂量76Gy。共设计7个计划,其中共面布野方案5个,分别为5、6、7、9野均匀分布和7野非均匀分布;非共面布野方案2个,分别为5、7野冠状交角照射。分别比较它们的剂量分布、剂量体积直方图、适形度指数等指标。结果所有7个共面和非共面计划的计划靶区剂量分布无明显差别,非共面计划比共面计划降低了直肠D50(50%体积所受剂量)剂量23%,但增加了股骨头剂量,膀胱的剂量大致相同;同时非共面计划还延长了治疗时间,摆位较麻烦。对于共面射野计划,当射野数目由5增至7时,增加照射野数目对靶区、直肠和膀胱剂量分布没有改善且会增加治疗时间,但能降低股骨头受量,靶区剂量均匀性、适合度指数提高,5、6野情况大致相同。当射野数由7野增加到9野时,股骨头受量和靶区剂量均匀性、适合度均无改善。结论5～7野共面调强计划可使前列腺肿瘤获得理想的剂量分布,共面、等角度分布的照射野设计简单、治疗实施效率高。非共面计划射野从5野增加到7野,剂量分布无改善。

Objective To find the optimal beam arrangement for prostate cancer treatment with several intensity modulated radiation therapy (IMRT) technique through comparison of different beam arrangements. Methods Seven IMRT plans were designed for each of 8 randomly chosen patients. With prescription dose in planned target volume(PTV)of 76?Gy, 5, 6, 7 ,9 equispaced beams , 7 non-equispaced axial beam arrangement and a 5-field , 7-field noncoplanar coronal crossfire beam arrangement were used. We compared the dose distribution, dose volume histograph(DVH), conformity index ,etc. of the different beam arrangements. Results There were little difference in PTV's coverage among all plans. Both crossfire beam arrangements showed a 23% mean decrease in D_~50 (dose for 50% volume of the rectum) to the rectum as compared with the axial beam arrangements, but with an increase in dose to the femoral head and the delivery time and a complicated manoeuvre of positioning. There was also little difference in the dose received by the bladder among all plans. For coplanar beam arrangements, the dose distribution in the target , rectum and bladder was not improved as the beam number increased from 5 to 7, though with the dose to the femoral head decreased, showing better dose conformity to the target. Five field and 6 field plans almost revealed the same situation. The dose distribution and conformity to the target and femoral head changed little when the beam number increased from 7 to 9. For noncoplanar beam arrangements, the dose distributions were not increased when the beam number increased from 5-7. Conclusions Five to 7 coplanar beams is able to provide desirable dose distribution for prostate tumor. It is easier and more efficient to design plans with equispaced coplanar beams than with non-equispaced coplanar or non-coplanar beams..