Comparison Of Dosimetry And Acute Toxicities Between IMRT And VMAT In Preoperative Concurrent Chemoradiotherapy For Locally Advanced Rectal Cancer

Part One:Dosimetric comparison between preoperative volumetric modulated arc therapy and five-fieldintensity modulated radiotherapy for rectal cancerObjective To compare the dosimetric characteristics of volumetric modulated arc therapy(VMAT) and five-field intensity modulated radiotherapy(5F-IMRT) in preoperative radiotherapy for rectal cancer.Methods Sixteen patients with rectal cancer who underwent preoperative chemo-radiotherapy were enrolled in this study. VMAT and 5F-IMRT plans were designed for each patient.The dose distribution in target volumes and organs at risk was evaluated according to the dose-volume histogram. Results Both plans could meet target dose specifications and normal tissue constraint.The CI was similar between the 5F-IMRT(0.88±0.04)and VMAT plans(0.90±0.03), which could satisfy 95% of prescribed dose for covered PTV.The HI of the VMAT plan was 1.06±0.01 compared to 1.05±0.01 of IMRT plans, without statistically significant differences(t=1.37, P>0.05). There was no significant difference for the key parameters(Dmean、Dmax)of risk organs such as intestine, bladder and femoral head in the two plans(P>0.05). There was no significant difference for the key parameters of irradiated volume such as V20,V30, V40 and V50 of risk organs between the 5F-IMRT and VMAT plans(P>0.05).The VMAT group also had significantly lower number of monitor units(MU)when compared with the 5F-IMRT plan group(P=0.000).Conclusion The dose distribution of VMAT and 5F-IMRT is similar in preoperative radiotherapy for rectal cancer, risk organs could be well protected.VMAT offers shorter treatment deliver time than IMRT, reduces treatment MU.Part Two:Comparison of acute toxicities between IMRT and VMAT in preoperative concurrent chemoradiotherapy for rectal cancerObjective To compare the acute toxicities between five-field intensitymodulated radiotherapy(IMRT)and volumetric modulated arc therapy(VMAT)in the preoperative concurrent chemoradiotherapy for locally advanced rectal cancer. To evaluate the feasibility of volumetric modulated arc therapy in the preoperative concurrent chemoradiotherapy for rectal cancer.Methods From March 2012 to November 2015,totally 78 locally advanced rectal cancer patients in our hospital treated by preoperative chemoradiotherapy based on VMAT(n=37) or 5F-IMRT(n=41) with concurrent capecitabine. All patients received preoperative radiotherapy at a dose of 50 Gy/25 fractions, concurrently with capecitabine(825mg/m2 PO BID,5d/w)。The acute toxicities between the two groups in the preoperative concurrent chemoradiotherapy and the rate of complete chemoradiotherapy were observed. Clinical follow-up data was analysis using SPSS 19.0 statistical software.Results All the patients completed the planned radiotherapy,and only 7 cases were interrupted with acute grade 3 toxicities. No significant difference in the incidence of toxicities was found between the VMAT and 5F-IMRT groups(8.0% vs 11.4%, P=0.498). The majority of toxicity was grade 1 to grade 2.No patient occurred grade IV toxicity. The most common acute toxicities in all patients were leucopenia(69.4%, grade≥35.8%), diarrhea(65.5%, grade I>320.7%), and radiodermatitis(62.0 %, grade≥37.9%). There were no significant differences in the incidence of most common acute toxicities between the VMAT and IMRT groups(P>0.05)Conclusion The preoperative concurrent chemoradiotherapy with capecitabine and VMAT was safe and well tolerate for patients with locally advanced rectal cancer,the incidence of acute toxicities was similar to 5F-IMRT.