子宫颈癌术后盆腔不同体外照射方法的剂量学研究

A comparative dosimetric study of conventional, conforinal and intensity-modulated radiotherapy in postoperative pelvic irradiation of cervical cancer

目的比较常规放疗（CRT）、三维适形放疗（3DCRT）及调强放疗（IMRT）方法在子宫颈癌靶体积剂量覆盖及危及器官（OAR）保护方面的差异，探讨子宫颈癌患者术后盆腔体外照射的合理方法。方法对10例子宫颈癌术后患者进行模拟CT增强扫描，在计划系统内勾画临床靶体积（CTV），CTV均匀外扩1．0cm生成计划靶体积（刚），同时勾画小肠、直肠、膀胱、骨髓、卵巢及股骨头作为OAR。进而设计出CRT、3DCRT及IMRT的3种治疗计划，对CRT要求参考点达到处方剂量45Gy，对3DCRT及IMRT要求95％的PTV达45Gy。应用等剂量曲线及剂量体积直方图对3种计划的CTV及OAR的剂量分布进行比较。结果CRT计划中CTV达45Gy的平均体积显著低于3DCRT、IMRT计划（Q=8．27、8．37，P值均〈0．01），而3DCRT和IMRT计划之间相似（Q=0．10，P〉0．05）。3DCRT和IMRT计划中小肠达30、45Gy的体积明显低于CRT。IMRT计划中直肠、膀胱达30、45Gy的体积均显著低于CRT，而3DCRT中仅直肠、膀胱达45Gy的体积显著低于CRT。3DCRT和IMRT使骨髓达30、45Gy剂量的体积明显低于CRT。4例卵巢移位者中2例在3DCRT及IMRT计划中，另2例在3种计划中卵巢平均受量全部超过300cGy。结论IMRT和3DCRT在提高靶体积内剂量及其均匀度，以及保护小肠、直肠和膀胱方面较CRT具备明显优势，以IMRT为最佳。在高剂量范围内，IMRT和3DCRT对骨髓的保护优势确定。对于移位悬吊的卵巢，IMRT、3DCRT及CRT均不能对其形成有效保护。

Objective To evaluate target-volume coverage and organ at risk （OAR） protection achieved with conventional radiotherapy （ CRT）, three dimensional conformal radiotherapy （ 3 DCRT）, and intensity-modulated radiotherapy（IMRT） through dosimetric comparison in patients with cervical cancer after hysterectomy. Methods The planning CT scans of 10 patients treated with pelvic radiation after hysterectomy for cervical cancer were used to generate CRT,3DCRT and IMRT plans for this study. Clinical target volume（CTV） was contoured on the individual axial CT slices of every patient. The CTV was then uniformly expanded by 1.0 cm to create the planning target volume （ PTV ）. The small bowel, rectum, bladder, bone marrow,ovaries,and femoral heads were outlined for the organ at risk（OAR） evaluation. The CRT,3DCRT and IMRT plans were generated using commercial planning software. CRT plan was prescribed to deliver 45 Gy to the reference point,while IMRT and 3DCRT plans were 45 Gy to 95% of the PTV. Isodose line and dose volume histograms（DVH） were used to evaluate the dose distribution in CTV and OAR. Results For 10 patients,the average volume of CTV receiving the prescribed dose of CRT was significantly lower than 3 DCRT（ Q = 8.27,P 〈 0.01 ） and IMRT （ Q = 8.37,P 〈 0.01 ）, respectively. Comparing with the CRT plan, the 3DCRT and IMRT plans notably reduced the volume of bowel at 30 and 45 Gy levels. The IMRT plan significantly spared rectum and bladder at 30 and 45 Gy levels comparing with the CRT （ P 〈 0.01 ） and 3DCRT（ P 〈 0.05 ） plans,while the 3DCRT plan significantly spared rectum and bladder at 45 Gy level com-paring with the CRT（ P 〈0.01 ） plans. For 4 patients with ovarian transposition,the average doses of ovary over 3 Gy were 2 patients with the 3DCRT and IMRT plans, and 2 with all three plans. Conclusions IMRT and 3DCRT are superior to CRT in improving dose coverage of target volume and sparing of OAR ,while IMRT being the best. The superiority of IMRT and 3DCRT is obvious in sparing bone marrow at high dose levels. IMRT,3DCRT and CRT could not spare the transposed ovary effectively.