宫颈癌术后不同射野数量对盆骨保护的调强放射治疗技术剂量学研究

Dosimetric analysis for the number of IMRT beams to pelvic bone for postoperative pelvic tumors

目的探讨在调强放射治疗技术(IMRT)中将盆骨作为危机器官进行计划设计的剂量学优势,研究不同射野数量对盆骨保护的IMRT的剂量学影响。方法 18例宫颈癌术后患者均进行CT扫描并勾画靶区。采用6MV X线,多野共面照射,每个患者设计4个IMRT计划,两个7野计划IMRT_(7f)和BMS-IMRT_(7f),1个5野BMS-IMRT_(5f)计划和9野BMS-IMRT_(9f)计划。IMRT_(7f)为未对盆骨限量的7野调强计划,BMS-IMRT_(5f)、BMS-IMRT_(7f)和BMS-IMRT_(9f)分别是将盆骨视为危机器官的5野、7野、9野调强计划。IMRT_(7f)和BMS-IMRT_(7f)比较,旨在分析对盆骨限量的计划对PTV适形性、均匀性和其他危机器官的剂量分布的影响。BMSIMRT_(5f)、BMS-IMRT_(7f)和BMS-IMRT_(9f)相互比较,研究不同射野数量对盆骨保护的剂量差异。结果 BMS-IMRT_(7f)与IMRT_(7f)相比,等剂量线在盆骨处分布更加紧凑。BMS-IMRT_(7f)与IMRT_(7f)在PTV适形性和均匀性上差异无统计意义(P>0.05),但是BMSIMRT_(7f)在盆骨保护上明显优于IMRT_(7f)(P<0.05)。BMS-IMRT_(9f)和BMS-IMRT_(7f)计划靶区的均匀性和适形性明显优于BMSIMRT_(5f)(P<0.05);在盆骨和小肠保护方面,BMS-IMRT_(5f)和BMS-IMRT_(7f)差异无统计意义(P>0.05);BMS-IMRT_(9f)在低剂量区照射面积最大,而在高剂量区照射面积最小。在直肠保护方面,BMS-IMRT_(7f)对直肠的照射面积最小。BMS-IMRT_(9f)对膀胱的保护最好,BMS-IMRT_(7f)次之。从跳数MU上分析,BMS-IMRT_(5f)跳数最少,BMS-IMRT_(9f)跳数最多。结论 BMS-IMRT_(7f)在不牺牲计划靶区的适形性和均匀性的基础上,较好的保护了盆骨,但略微增大直肠、小肠和膀胱的高剂量区。BMS-IMRT_(7f)在PTV适形性、均匀性和危机器官保护上,优于BMS-IMRT_(5f),略差于BMS-IMRT_(9f)。BMS-IMRT_(9f)跳数较多,治疗时间较长。从剂量和实际执行效率来说,BMS-IMRT_(7f)更适合临床应用。

Objective To investigate the dosimetric advantages of IMRT plans which regard pelvic bone as an organ at risk, and explore the dosimetric effect of the beam number on pelvic bone during cervical IMRT plans. Methods The target areas of 18 cases of cervical cancer patients were depicted after CT scans. 6Mv X-ray and multi-field coplanar plan were performed. Four coplanar plans were performed on every case, including IMRT7f、BMS-IMRT5f、BMS-IMRT7f and BMS-IMRT9f. The pelvic bones were not considered as organ at risk in IMRT7f.While, they were regarded as organ at risk in BMS-IMRT5f、BMS-IMRT7f and BMS-IMRT9f. The comparison between IMRT7f and BMS-IMRT7f was used to analyze the effect of different treatment plans in conformability and homogeneity of PTV and dose distribution in organs at risk. The comparisons of BMS-IMRT5f, BMS-IMRT7f and BMS-IMRT9f were used to investigate the dosimetric difference of the beam number on cervical IMRT plans. Results Compared with IMRT7f, BMS-IMRT7f had more compact isodose lines in the pelvic bone region. The difference between BMS-IMRT7f and IMRT7f in conformability and homogeneity of PTV was not significant. BMS-IMRT7f was better than IMRT7f in pelvic bone protection with significant difference. Both of BMS-IMRT9f and BMS-IMRT7f had better coverage and homogeneity of PTV than BMS-IMRT5f. The difference between BMS-IMRT5f and BMS-IMRT7f in pelvis and intestinal protection was not significant. BMS-IMRT9f had a large filed in lower dose area, while it had a small field in higher dose area. In terms of rectal protection, BMS-IMRT7f had a minimum filed size on rectum. BMS-IMRT9f was best protected against the bladder, followed by BMS-IMRT7f. The number of BMS-IMRT5f hops was the least, and the number of BMS-IMRT9f hops was the largest. Conclusion BMS-IMRT7f protects the pelvis.It increases the high dose of the rectum, small intestine and bladder without sacrificing the conformability and uniformity of PTV. BMS-IMRT7f is superior to BMS-IMRT5f in PTV conformance, homogeneity and organ protection. BMS-IMRT9f hops more with longer treatment time. BMS-IMRT7f is more suitable for clinical use in terms of dose and actual implementation efficiency.