Comparison of volumetric-modulated arc therapy using simultaneous integrated boosts (SIB-VMAT) of 45 Gy/55 Gy in 25 fractions with conventional radiotherapy in preoperative chemoradiation for rectal cancers: a propensity score case-matched analysis

The aim of this retrospective study was to compare volumetric-modulated arc therapy using simultaneous integrated boosts (SIB-VMAT) of 45 Gy/55 Gy in 25 fractions with three-dimensional conformal radiotherapy (3D-CRT) in preoperative chemoradiation for rectal cancers. In the propensity score-matching analysis of 1:2, we selected 60 patients from the SIB-VMAT group and 120patients from the 3D-CRT group matched pairings out of 145 patients between 2005 and 2015. The regimen of concurrent combined chemotherapy was oral uracil/tegafur plus leucovorin with/without irinotecan. There were no significant differences between the two groups, in pathological complete response rates (pCR) (11% in the 3D-CRT group vs. 17% in the SIB-VMAT group, P = 0.39), pathological response rates (44% vs. 60%, P = 0.77), disease-free survival (P = 0.32), or local control (P = 0.52). The SIB-VMAT method marginally improved the rate of pathological grade 2-3 effects and the OS was significantly better in patients with grade 2-3 effects. Recurrence was seen in 36 patients (30%) in the 3D-CRT group and 19 patients (32%) in the SIB-VMAT group. The first distant recurrence site in the SIB-VMAT group was liver in 6 patients and lung in 8 patients. The obvious radiation-induced late toxicity in the SIB-VMAT group was recto-vesical fistula in two patients. The SIB-VMAT may be a promising method for preoperative CRT of rectal cancer.