局部晚期直肠癌术前VMAT同期加量剂量学研究

A dosimetric study of volumetric modulated arc therapy with a simultaneous integrated boost for preoperative chemoradiotherapy in patients with locally advanced rectal cancer

目的 探讨开展直肠癌术前VMAT同期加量（SIB-VMAT58.75 Gy）剂量学可行性,为临床应用提供依据。方法 对9例Ⅱ—Ⅲ期直肠癌术前放化疗患者分别行SIB-VMAT58.75 Gy和非同期加量VMAT （VMAT50.00 Gy）,SIB-VMAT58.75 Gy剂量分割模式为局部直肠病变及阳性淋巴结给予58.25 Gy分25次（2.35 Gy/次）,盆腔淋巴引流区给予50 Gy分25次（2.0 Gy/次）;VMAT50.00 Gy剂量分割模式为盆腔淋巴引流区50 Gy分25次（2.0 Gy/次）。利用DVH评价靶区CI、HI和OAR受量。配对t检验或配对非参数秩和检验。结果 两种计划均能满足靶区处方剂量要求;PTV两组CI相近（1.0±0.0、1.0±0.0,P〉0.05）;HISIB-VMAT58.75 Gy组差于HIVMAT50.00 Gy组（0.2±0.2、0.1±0.0,P〈0.05）。SIB-VMAT58.75 Gy较VMAT50.00 Gy小肠D2 cm^3稍增加（P=0.038）,小肠、膀胱、股骨头、骨盆的V10—V50两种计划相近（P均〉0.05）。结论 SIB-VMAT58.75 Gy计划可以满足靶区处方剂量及OAR剂量限制要求,在剂量学上安全可行,具体疗效及不良反应有待于临床研究进一步验证。

Objective To investigate the dosimetric feasibility of volumetric modulated arc therapy （VMAT） with a simultaneous integrated boost （SIB-VMAT58.75 Gy） for preoperative chemoradiotherapy inpatients with locally advanced rectal cancer （LARC）,and to provide a basis for clinical practice. MethodsNine patients with stage Ⅱ-Ⅲ rectal cancer who underwent preoperative concurrent chemoradiotherapy were involved in the study,and two plans were performed for each patient：SIB-VMAT58.75 Gy and VMAT50.00 Gy. For the SIB-VMAT58.75 Gy plan,the prescribed dose was 58.75 Gy （2.35 Gy/fraction） for the local rectal tumor and positive lymph nodes （GTV 58.75 Gy）,and 50 Gy （2 Gy/fraction） for the regions at high risk of harboring microscopic disease （pelvic lymphatic drainage area）（PTV50 Gy）.For the VMAT50.00 Gy plan,the prescribed dose was 50 Gy （2 Gy/fraction） for the regions at high risk of harboring microscopic disease （pelvic lymphatic drainage area） without a boost. The conformity index （CI）,homogeneity index （HI）,and dose for target areas and organs at risk （OAR） were assessed according to the dose-volume histogram. The paired t-test or nonparametric rank test was used to compare the differences between the two plans. Resutls Both plans met the prescription goal for PTV dose coverage. There was no significant difference in CI for the PTV between the two plans （1.0±0.0 vs. 1.0±0.0,P〉0.05）.The SIB-VMAT58.75 Gy plan had a worse HI than the VMAT50.00 Gy plan （0.2±0.2 vs. 0.1±0.0,P〈0.05）.There was no significant difference in V10-V50 of the small intestine,bladder,femoral heads,and pelvis between the two plans （P〉0.05）,but D2 cm^3 of the small intestine was significantly higher in the SIB-VMAT58.75 Gy plan than in the VMAT50.00 Gy plan （P=0.038）. Conclutions The SIB-VMAT58.75 Gy plan for LARC achieves required target volume dose coverage and OAR dose constraints,which is safe and feasible in terms of dosimetry,and its clinical efficacy and adverse effects need further evaluation.