直肠癌盆腔常规放疗与三维适形放疗的剂量学研究

Dosimetry study on the conventional and three dimensional conformal radiation treatment planning protocols for rectal cancer

目的比较直肠癌盆腔常规放疗和三维适形放疗（3DCRT）对治疗靶区及盆腔正常组织和器官的影响。方法对36例接受3DCRT的直肠癌患者CT定位图像资料进行研究,在连续的CT图像上分别勾画出肿瘤临床靶区（CTV）和危及组织、器官（大小肠、膀胱、盆腔骨、股骨头颈）,用三维治疗计划模拟出2种三维治疗方式（3、4个野计划）和3种常规治疗方式（2、3、4个野计划）,即3D-3、3D4、2D-2、2D-3、2D4治疗计划。通过剂量-体积直方图（DVH）的分析来评价这5种治疗方式对CTV和危及组织、器官的影响。结果5种治疗方式的D95、V95都达到97%以上,3D治疗的适形指数（CI）明显大于2D治疗,剂量不均匀指数（DI）4个野方式要明显小于3个野方式。3D-3与2D-3、3D-4与2D-4相比大小肠受照平均剂量分别要减少28．5%和25．7%,差异有统计学意义。在45 Gy高剂量区3D-3与2D-2、3D-3与2D-3和3D4与2D4相比分别要减少80．8%、51．1%和54．7%的大小肠受照体积。对盆腔骨和膀胱的影响,无论是平均受照剂量还是35、45 Gy的高剂量受照体积3D方式均要明显优于2D方式,且差异有统计学意义。对股骨头颈的影响3D方式明显优于2D方式。结论尽管直肠癌盆腔常规放疗和3DCRT对靶区CTV的影响差别不大,但对盆腔正常组织和器官的影响却有明显不同,3DCRT更能有效地保护正常组织和器官。

Objective To compare the dose distribution of clinical target volume （ CTV）, in normal tissues and organs for patients with rectal cancer on the conventional radiotherapy （2D） and three dimensional conformal radiation treatment （3DCRT）. Methods The CT image data of 36 rectal cancer patients treated with 3DCRT were studied. The CTV, small bowel, colon, bladder, pelvic bone marrow, and femoral head and neck were contoured on consecutive axial slices of CT images. Two 3 DCRT and three conventional treatment planning protocols were simulated using three dimensional treatment planning system（ CMS Focus 2.31 ） , were defined as 3D-3,3D-4,2D-2,2D-3,2D-4. The difference of five treatment planning protocols on the CTV and normal structure by analysis of dose-volume histograms （ DVHs ） were compared. Results The D95 and V95 of these five protocols all exceeded 97%. The conformity index（CI） of 3D was obviously larger than that of 2D protocol. The dose inhomogeneity（DI） in 4 DCRT was less than that of 3 DCRT. The 3D as compared with the 2D, significantly reduced the mean dose of 45 Gy to the small bowel and colon. The 3D-3 as compared with the 2D-3, the 3D-4 as compared with the 2D-4, the mean dose of small bowel and colon was reduced by 28.5% and 25.7%, respectively. The 3D-3 as compared with the 2D-2, the 3D- 3 as compared with the 2D-3 and the 3 D-4 as compared with the 2D-4, the percentage volume of small bowel and colon which received 45 Gy was reduced by 80.8%, 51.1% and 54.7% , respectively. Either the mean dose, or the percentage volume receiving 35 Gy and 45 Gy to the pelvic bone and bladder, the 3D planning protocols had advanage over the 2D planning protocols. The V45 of bladder in 2D-2 planning protocol was the highest in all planning protocols, exceeding 98% , but the highest V45 of bladder was only 50% in the other planning protocols. Conclusions Even though the difference in pelvic CTV of rectal cancer patients between the conventional radiotherapy and 3 DCRT was insignificant, there is significant difference in the pelvic normal tissues and organs. 3DCRT is able to effectively protect all these organs.