Preoperative intensity-modulated and image-guided radiotherapy with a simultaneous integrated boost in locally advanced rectal cancer: report on late toxicity and outcome.

Background And Purpose: The addition of chemotherapy to preoperative radiotherapy has been established as the standard of care for patients with cT3-4 rectal cancer. As an alternative strategy, we explored intensity-modulated and image-guided radiotherapy (IMRT-IGRT) with a simultaneous integrated boost (SIB) in a prospective phase II study. Here, we report outcome and late toxicity after a median follow-up of 54 months.

Methods And Materials: A total of 108 patients were treated preoperatively with IMRT-IGRT, delivering a dose of 46 Gy in fractions of 2 Gy. Patients (n=57) displaying an anticipated circumferential resection margin (CRM) of less than 2mm based on magnetic resonance imaging received a SIB to the tumor up to a total dose of 55.2 Gy.

Results: The absolute incidence of grade ≥3 late gastrointestinal and urinary toxicity was 9% and 4%, respectively, with a 13% rate of any grade ≥3 late toxicity. The actuarial 5-year local control (LC), progression-free survival (PFS) and overall survival (OS) were 97%, 57%, and 68%. On multivariate analysis, R1 resection and pN2 disease were associated with significantly impaired OS.

Conclusions: The use of preoperative IMRT-IGRT with a SIB resulted in a high 5-year LC rate and non-negligible late toxicity.