Dosimetric study of VMAT for definitive radiotherapy of elderly patients with low rectal cancer

LIU Qiulian; CAO Junda; WAN Xiaofeng; LI Zijun; XIA Yun; WANG Zhi; GONG Minyong

Abstract：Objective:To compare the dose difference between volumetric modulated arc therapy (VMAT) and 7 F-ntensltymodulated radiation therapy (7 F-IMRT) in definitive radiotherapy for elderly patients with low rectal cancer.Methods:Twenty-one patients with low rectal cancer conducted definitive radiotherapy were selected with Pinnacle 9.0.VMAT and 7 F-IMRT plans were respectively designed for each patient.Dose-volume histogram was applied to compare the dose distribution of target volumes and OARs.Results:Intensity modulated radiation therapy 7 F-IMRT and VMAT programs can meet the design requirements of the plan.The conformality index (CI) of VMAT and 7 F-IMRT were 1.16 and 1.22 respectively.The conformability of VMAT is better than IMRT (P＜0.05).The uniformity index (HI) is 0.07 and 0.08 respectively.The uniformity of VMAT is better than IMRT.The difference was not statistically significant (P＞0.05).In the compromised organ dose, the low and high dose affected volume of VMAT technology was lower than IMRT technology.For the intestinal VMAT increased the medium dose area V30 and V40, the V15 and V50 of small intestine in VMAT plans were lower than that in 7 F-IMRT plans.The Dmean, V30and V50 of bilateral femoral head were no significant differences between two plans.The monitor unit of VMAT was significantly lower than that of 7 F-IMRT plans (372.20 vs 528.06, P＜0.05).Compared with 7 F-IMRT plans, VMAT plans showed shorter treatment time (169 s vs 410 s, P＜0.05).Conclusion:Compared with 7 F-IMRT plans, VMAT plans have better HI and CI, with obvious advantages in protecting bladder and small intestine.The treatment time and control points are lower in VMAT plans.