Dosimetric And Clinical Research For Postoperative Radiotherapy Of Rectal Cancer

Part one：Dosimetric Comparison of Three-dimensional ConformalRadiation Therapy, Intensity-modulation Radiation Therapy andHelical Tomotherapy for Postoperative Rectal CancerObjective: To evaluate the dosimetric characteristics in helical tomotherapy (HT),intensity-modulated radiation therapy (IMRT) and three-dimensional conformalradiation therapy (3D-CRT) for postoperative radiotherapy of rectal cancer.Methods: Ten male patients underwent postoperative radiotherapy with stage Ⅱor Ⅲrectal cancer were enrolled in this study retrospectively. HT, IMRT and3D-CRTplans were produced for each patient, respectively. The prescription dose was50Gy into25fractions, covering at least95％of the planning target volume.Dose-volumeconstraints of OARs were as follow: D50to the pelvic bone <30Gy, D50to the smallbowel <30Gy, D50to the bladder <30Gy, D5to the femoral head <45Gy. Comparisonparameters such as CI, HI and dose-volume of OARs and target between each plan, toassess the target dose distribution and the irradiation volume of normal tissue.Results: All plans could meet the need of the prescription dose. Dose-volumeconstraints of OARs were found acceptable in HT and IMRT plans except3D-CRTplans. Conformity index of HT, IMRT, and3D-CRT plans were0.86,0.82and0.62(F=206.81，P<0.001), homogeneity index were0.001,0.157and0.205(c2=15.8，P<0.001), respectively.3D-CRT plans had greater volumes than HT plans and IMRTplans in the high-dose region, such as pelvic V50, bladder V40, bowel V50, femoral headD5(P<0.05), but the differences between HT plans and IMRT plans were notstatistically significant (P>0.05). The V15of small bowel was71.1%for HT plans,63.3%for IMRT plans and67.7%for3DCRT plans, but the difference was notstatistically significant (F=1.69, P=0.221). Conclusion: All of the HT plans, IMRT plans and3D-CRT plans are able to meetthe prescription dose requirement of target. HT plans show better dose homogeneity andtarget conformity than IMRT plans, and IMRT plans are superior to3D-CRT plans. HTplans are able to meet all of the OARs dose-volume constrains and superior to IMRTplans.3DCRT technique is practical and easy to generate, however, it is unsatisfyingwhen it comes to the protection of OARs. Part two：Postoperative Chemoradiotherapy in StageⅡ/ⅢRectalCancer:52Cases of Clinical AnalysisObjective: To evaluate the curative effect, prognosis factors and adverse sideeffect of postoperative chemoradiotherapy in stage Ⅱ/Ⅲ rectal cancer.Methods: Between May2008and May2012,52patients have stageⅡ/Ⅲ rectalcancer and received radical operation and postoperative chemoradiotherapy wereincluded in our retrospective study. Three-dimensional conformal radiotherapy andintensity modulation radiotherapy were respectively delivered to22patients, helicaltomotherapy were delivered to8patients, and prescription dose was50Gy/25F. Everypatient received at least one circle of sequential chemotherapy. Acute and late adverseside effects were evaluated by RTOG/EORTC criteria.Results: The overall3-year survival rate and disease-free survival was80%and73%, respectively, the average survival time was46.6months, and the3-years of localcontrol rate was81%. The factors of gentle, age and stage influenced the survival rateby univariate analysis (P<0.05). Cox proportional hazards model study show that stagewas available independent prognostic factor (RR=1.07, P=0.04). Grade1-2acute andlate adverse side effects were observed in most of the patients. There was no statisticallydifference in every grade of adverse side effect among3DCRT, IMRT and HT. Conclusion: Stage is the available independent prognostic factor to the stage Ⅱ/Ⅲ postoperative chemoradiotherapy rectal cancer. The adverse side effects ofpostoperative chemoradiotherapy among3DCRT, IMRT and HT are similar.