Application of MRI simulation in delineation of gross tumor volume in pre-operative radiotherapy for low rectal carcinoma / 中华放射医学与防护杂志

ABSTRACT

Objective To explore the value of MRI simulation in the pre-operative radiotherapy for locally advanced low rectal carcinoma.Methods A total of 40 patients diagnosed with locally advanced low rectal carcinoma by endoscopic biopsy and radiological staging examinations were included in this study.There were 22 male and 18 female with nedian age 58 years (range 31-80).Patients underwent CT and MRI simulation scanning in the same position and fixing device.GTV under CT images and MRI inages were delineated respectively by two experienced radiologists.Primary tumor length,tumor volume and distance of distal tumor from the anal verge were calculated by treatment planning system(TPS).The two groups of data were compared.Results The distance of distal tumor to the anal verge were all no more than 5 cm on digital examination.The mean length of GTVcT was remarkably longer than that of GTVMRI [(5.21 ±1.65) cm vs.(4.46 ± 1.51) cm,t =5.059,P ＜0.05].The mean volume of GTVcTWaS significantly larger than that of GTVMRI[(55.71 ±31.57) cm3vs.(44.02 ±25.11) cm3,t=6.977,P＜ 0.05)].The mean distance of distal tumor to the anal verge was (3.72 ± 0.93) cm,significantly longer than that of lower bounds of GTVCT to the anal verge,which had a high consistency with GTVMRI.The IMRT plan was based on CT-MRI fusion images.There were no 3-4 grade adverse effects of radiotherapy.The overall pCR rate was 32.5％.Conclusions MRI simulation could define smaller GTV and more precise lower bounds than CT.With improved accuracy of target volumes contours,the application of MRI simulation may promote the efficacy of radiotherapy and result in a reduction in the incidence of toxicities.