Dosimetric analysis of preoperative three-dimensional conformal and preoperative intensity modulated radiotherapy for rectal cancer

Abstract

Objective To compare the dose distribution of the three-dimensional conformal radiotherapy(3D-CRT)and 5-field or 7-field intensity modulated radiation therapy(IMRT), and to explore the value of IMRT in preoperative radiotherapy for rectal cancer.Methods Ten rectal cancer patients treated with preoperative combination radiotherapy and chemotherapy were enrolled in this study. 3D-CRT plan and the 5.field or 7-field IMRT plans were performed for each patient.The conformal index (CI),heterogeneity index(HI)of the planning target volume(PTV)and the dose of normal organs of 3D-CRT plan(3D-CRTp)and the 5-field or 7-field IMRT plans(IMRT5fp or IMRT7fp)were analyzed with the dose-volume histogram.Results The CI values of PTV were 0.91,0.87 and 0.78 in IMRT7fpIMRT5fp and 3D- CRT but with IMRT7fp>IMRT5fp>3D-CRTp(t=-5.69、-8.91,P IMRT7fp>3D- CRTp(t=3.41、-6.89,P<0.01),respectively.The ratio of dose volume were 0.08,0.10 and 0.19(t=2.79、3.52,P<0.05)in IMRT7fp,IMRT5fp and 3D- CRTp on the small intestine V50,with 0.07,0.10 and 0.19(t=2.58、3.40,P<0.05)in IMRT7fp,IMRT5fp and 3D-CRTp on the bladder V50 and 0.01,0.01 and 0.05(t=3.00、3.17,P<0.01)in IMRT7fp,IMRT5fp and 3D- CRTp on the fomoral head V45.The ratio of dose volume were 0.31 and 0.38(t=3.91,P<0.01)in IMRT7fp and IMRT5fp on the bone marrow V50,with 0.07 and 0.10 in IMRT7fp and IMRT5fp on bladder V45.Conclusions IMRT plan is superior to 3 D- CRT plan in dose conformal degrees of PTV with preoperative radiotherapy of rectal cancer and can significantly protect the normal tissues.The 7-field IMRT plan might be the optimal plan for dose conformal degree and dose uniformity compared with 5-field IMRT. Key words: Rectal carcinoma; Preoperative radiotherapy; Three-dimensional conformal radiotherapy; Intensity-modulated radiotherapy; Dosimetry