不同角度固定野动态调强在直肠癌术前放疗中的剂量学比较

Dosimetric Comparison of Different Angle with Dynamic Intensity Modulated Radiotherapy in Preoperative Radiotherapy of Rectal Cancer

目的:比较两种不同角度的固定野动态调强(Dynamic Intensity Modulated Radiotherapy,dIMRT)在直肠癌术前放疗中的剂量学差异。方法:选取10例直肠癌术前患者分别设计5F-00-dIMRT与5F-1800-dIMRT两组计划,PTV处方剂量为50Gy/25次。在95%体积的PTV达到处方剂量前提下,比较两组计划的剂量体积直方图(DVH)、靶区和危及器官剂量、靶区适形度指数(CI)、均匀性指数(HI)、正常组织低剂量体积(B-P)、总机器跳数(MU)以及治疗时间(Treatment Time,TT)。结果:对于PTV的Dmean来说,5F-00-dIMRT低于5F-1800-dIMRT(P<0.05);5F-00-dIMRT的靶区适形度指数优于5F-1800-dIMRT(P<0.05),而5F-00-dIMRT的均匀性指数略优于5F-1800-dIMRT,但差异无统计学意义。在膀胱的Dmean、D5与V30中5F-00-dIMRT低于5F-1800-dIMRT(P<0.05),其余V20、V40、V50间差异无统计学意义。小肠V30中5F-00-dIMRT低于5F-1800-dIMRT(P<0.05),而Dmean、D5、V20中5F-00-dIMRT高于5F-1800-dIMRT,V40、V50中5F-00-dIMRT低于5F-1800-dIMRT,但差异均无统计学意义。双侧股骨头的Dmean、D5、V20、V30,5F-00-dIMRT显著高于5F-1800-dIMRT(P<0.05),V40则明显低于5F-1800-dIMRT(P<0.05)。相对于5F-00-dIMRT来说,B-P的V5、V10、V15高于5F-1800-dIMRT,V20低于5F-1800-dIMRT,差异均无统计学意义,而V30低于5F-1800-dIMRT,差异具有统计学意义(P<0.05)。5F-00-dIMRT的MU较5F-1800-dIMRT略少(P>0.05)。5F-00-dIMRT的治疗时间(TT)较5F-1800-dIMRT略少(P>0.05)。结论:两组计划均能够满足临床治疗需要,5F-00-dIMRT较5F-1800-dIMRT提高了靶区的适形度,能更好地保护膀胱、小肠、双侧股骨头的V40和正常组织低剂量区(B-P)V30的剂量,然而对双侧股骨头的高剂量热点与低剂量区的损伤确更大。

Objective： To compare the dosimetric difference with different fixed gantry angle dynamic intensity modulated ra diotherapy （dlMRT） in the preoperative radiotherapy for rectal cancer. Methods： Ten sets of plans with 5F-0°-dlMRT and 5F-180°-dlMRT were created for 10 consecutive patients. Dose prescription was 50 Gy in 25 fractions. All plans were normal ized to 50 Gy to 95% of PTV. The dose volume histogram （DVH）, target and risk organ doses, conformity indexes （CI）, homo geneity indexes （H/）, low dose volume of normal tissue（B-P）, total monitor units（MU） and treatment time （TT） were compared between the different techniques. Results： Plans with 5F-0°-dlMRT provided the better mean dose （P〈0.05） and conformity in dexes （P〈0.05）, and similar homogeneity as compared with 5F-180°-dIMRT. Bladder Dmean, D5 and V30 were lower in 5F-0°-dlM- RT than 5F-180°-dIMRT （P〈0.05）. Plans with 5F-0°-dlMRT had significantly lower intestine V30 than 5F-180°-dlMRT（P〈0.05）, and higher intestine Dmean, D5, V20 and lower intestine V4o, Vs0 than 5F-180°-dlMRT （P〉0.05）. Plans with 5F-0°-dlMRT provided significantly higher Dmean and Ds, V20 and V30 of bilateral femoral head（P〈0.05）, but lower V40 than 5F-180°-dIMRT （P〈0.05）.Plans with 5F-0^-dlMRT had lower B-P V30 （P〈0.05）, but no significantly different higher B-P V5, V10, V15 and lower B-P V2o as compared with 5F-180°-dlMRT. 5F-0°-dlMRT plans reduced the total MU （P〉0.05）, as well as the treatment time （TT） （P〉0.05）, as compared with 5F-180°-dlMRT respectively. Conclusions： Two sets of plans are able to meet the needs of the clinical treat- ment, as compared with 5F-180°-dlMRT, 5F-0°-dlMRT showing better target coverage, bladder, intenstine, femoral head of V40 and normal tissues（B-P） V3o dose sparing, but the max dose and low dose of femoral head area of the damage is greater.