Objective To investigate the dosimetric feasibility of volumetric modulated arc therapy (VMAT)with a simultaneous integrated boost(SIB-VMAT58.75 Gy)for preoperative chemoradiotherapy in patients with locally advanced rectal cancer(LARC),and to provide a basis for clinical practice.Methods Nine patients with stage Ⅱ-Ⅲ rectal cancer who underwent preoperative concurrent chemoradiotherapy were involved in the study,and two plans were performed for each patient:SIB-VMAT58.75 Gy and VMAT50.00 Gy. For the SIB-VMAT58.75 Gy plan,the prescribed dose was 58.75 Gy(2.35 Gy/fraction)for the local rectal tumor and positive lymph nodes(GTV 58.75 Gy),and 50 Gy(2 Gy/fraction)for the regions at high risk of harboring microscopic disease(pelvic lymphatic drainage area)(PTV 50Gy).For the VMAT50.00 Gy plan,the prescribed dose was 50 Gy(2 Gy/fraction)for the regions at high risk of harboring microscopic disease(pelvic lymphatic drainage area)without a boost. The conformity index(CI),homogeneity index (HI),and dose for target areas and organs at risk(OAR)were assessed according to the dose-volume histogram. The paired t-test or nonparametric rank test was used to compare the differences between the two plans. Results Both plans met the prescription goal for PTV dose coverage. There was no significant difference in CI for the PTV between the two plans(1.0±0.0 vs. 1.0±0.0,P>0.05).The SIB-VMAT58.75 Gy plan had a worse HI than the VMAT50.00 Gy plan(0.2± 0.2 vs. 0.1± 0.0,P<0.05).There was no significant difference in V10-V50of the small intestine,bladder,femoral heads,and pelvis between the two plans(P>0.05),but D 2 cm3of the small intestine was significantly higher in the SIB-VMAT58.75 Gy plan than in the VMAT50.00 Gy plan(P=0.038). Conclusions The SIB-VMAT58.75 Gy plan for LARC achieves required target volume dose coverage and OAR dose constraints,which is safe and feasible in terms of dosimetry,and its clinical efficacy and adverse effects need further evaluation.