Dosimetric Study Of Different Techniques In Postoperative Radiotherapy Of Rectal Cancer

Objective: This study compared the dosimetric differences of targetvolume and organs at risk between three dimensional conformal radiationtherapy and intensity modulated conformal radiation therapy in postoperativeradiotherapy of rectal cancer in order to provide references for clinic work.Methods and methods: From May2010to June2011,15postoperative（Dixon） rectal cancer patients who were treated in the department ofradiotherapy of cancer center of the first hospital of Jilin university wereenrolled in this study. Patients were asked to make gastrointestinal preparationand keep bladder distended before the treatment planning computedtomographic scan and then transverse images were taken at5mm-thicknessintervals with patients in the prone position with the belly board device andSiemens Somatom Sensation Open. The reconstructed images were transmittedto the Pinnacle3system. The doctor contoured the target volumes and organs atrisk then3D-CRT and IMRT plan were performed for each patient. Prescriptiondose was set95percent of PTV acceptable dose and the limited doses of organsat risk: V50of small intestines＜50﹪,V50of bladder＜50﹪and V50of femoralhead＜5﹪. We evaluated plans by the dose-volume histograms and dose curve.The main evaluation parameters were CI, HI, Dmax, Dmean and Dmin, V20,V40and V50of small intestines, V40and V50of bladder and V50of femoral head.Results：The comparisons were made between3D-CRT plan and IMRTplan, CI of PTV were0.73±0.02and0.85±0.015, HI of PTV were1.11±0.01and1.06±0.005respectively. There were significant differences in CI, HI,Dmax, Dmean and Dmin. IMRT plans showed a significant superior uniformityand conformity over3D-CRT plans. The doses of organs at risk of two plans were both below the limited doses of normal organs. Compared with3D-CRTplans, the V20of small intestines in IMRT plans was increased by33.9﹪, theV40and V50of small intestines were decreased by38.6﹪and47.0﹪respectively. The V40and V50of bladder were decreased by35.7﹪and54.0﹪and the V50of femoral head was decreased by81.9﹪.Conclusion: IMRT plans showed a significant superior uniformity andconformity over3D-CRT plans in postoperative radiotherapy of rectal cancer.3D-CRT and IMRT plans both had good protections for organs at risk such assmall intestines, bladder and femoral head. IMRT had a dose distributionadvantage in the irradiated volume of higher dose but the irradiated volume ofsmall intestines at lower dose was larger than3D-CRT.