简化调强技术在宫颈癌外照射中应用的剂量学研究

Dosimetric study of simplified intensity modulated radiation therapy for cervical cancer

目的通过比较宫颈癌盆腔三维适形放疗（3DCRT）、简化调强放疗（sIMRT）和调强放疗（IMRT）技术靶区剂量分布均匀度、适形度，危及器官受照体积、剂量，以及实施治疗时间的影响，探讨sIMRT用于宫颈癌放疗的可行性。方法10例常规体外和腔内放疗的Ⅱb-Ⅲb宫颈癌患者，放疗前行CT扫描并勾画靶区，临床靶体积（CTV）包括子宫、宫颈、阴道等原发肿瘤区域及髂总、髂外、髂内、闭孔、骶前淋巴结等区域和其周围组织，计划靶体积（PTV）以CTV为基础外放前向10mm、余各方向5mm形成PTV。处方剂量95％PTV45Gy（1．8Gy／次，共25次），通过分析剂量体积直方图、适形指数、均匀指数和实施治疗时间，比较3种治疗技术的优缺点。结果3种治疗计划PTV剂量分布的均匀度3DCRT最好，而IMRT与sIMRT相似；剂量分布的适形度sIMRT逊于IMRT而强于3DCRT。对膀胱的保护IMRT明显优于sIMRT，而sIMRT优于3DCRT；对小肠的保护sIMRT显著优于3DCRT，而IMRT并不比sIMRT具有更多优势；对直肠的保护sIMRT优于3DCRT，而逊于IMRT，IMRT的优点主要体现在高剂量区。实际占机时问3DCRT约4min，sIMRT约10min，IMRT约18min。结论sIMRT可减轻工作人员劳动强度，缩短治疗时间，简化验证程序。sIMRT适用于宫颈癌放疗且是一种性价比较高的放疗技术。

Objective To compare the homogeneity and conformity of dose distribution in the target and the dose to the organs at risk among 3-dimensional conformal radiation therapy （3DCRT）, intensity modulated radiation therapy （IMRT） and simplified intensity modulated radiation therapy （sIMRT） , and then to evaluate the clinical value of sIMRT for cervical cancer. Methods Ten patients with cervical cancer receiving radical radiotherapy and brachytherapy were enrolled. Before radiotherapy, CT was performed and target volumes were delineated. The clinical target volume （CTV） included supravaginal portion, cervical stump, paracervical tissue, common iliac lymph nodes, internal and external iliae lymph nodes, obturator lymph nodes, sacral lymph nodes, and the surrounding tissues. If the vagina was involved, the target volume included the whole vagina. Margins between planning target volume （PTV） and CTV were 10 mm in the anterior direction, and 5 mm in other directions. The prescribed dose was 95% PTV receiving 45 Gy in 25 fractions of 1.8 Gy. The dose volume histogram, conformity index, homogeneity index and treatment time per faction were compared. Results Among the three radiotherapy techniques, 3DCRT had the best homogeneity of dose distribution, while there was no significant difference between IMRT and sIMRT. According to the conformity of dose distribution, sIMRT was better than 3DCRT, but worse than IMRT. Comparing the bladder sparing, IMRT was the best followed by slMRT. The volume of the small intestine receiving high dose was increased significantly with sIMRT when compared with IMRT. And the treatment time per faction was 4 , 1 0 and 1 8 minutes for 3 DCRT , sIMRT and IMRT, respectively. Conclusions sIMRT could re - duce the work intensity of the staff , shorten the treatment time per fraction , and simplify the authenticate procedure, which is cost-effective and suitable in the treatment of cervical cancer.