Utilization of short-course radiation therapy for patients with nonmetastatic rectal adenocarcinoma in the United States.

Purpose: Preoperative short-course radiation therapy (SCRT) for patients with nonmetastatic rectal adenocarcinoma has been studied in European trials, but is not often used in the United States. We aim to describe the utilization of preoperative SCRT among patients with nonmetastatic rectal cancer in the National Cancer Database and describe factors associated with its use.

Methods and materials: The National Cancer Database was queried for patients treated with preoperative radiation therapy followed by surgery for nonmetastatic rectal adenocarcinoma between 2004 and 2014. Patient, tumor, and treatment-related characteristics were compared between patients treated with SCRT (20-25 Gy in <7 fractions) and patients treated with long-course radiation therapy (45-70 Gy in ≥ 25 fractions). Univariate and multivariate Cox regression analyses were used to evaluate factors associated with overall survival. Survival rates were compared using an inverse-probability-weighted regression adjustment method.

Results: A total of 42,336 patients were included for analysis of which 41,867 patients (98.9%) were treated with long-course radiation therapy and 469 patients (1.1%) with SCRT. Patients treated with SCRT were older, had more comorbidities, had earlier T-stage, and were more likely to be clinically node-negative. Patients treated with SCRT were more likely to be treated at an academic center, have Medicare insurance, and be treated without chemotherapy. Patients treated with SCRT had lower pathological complete response rates (4.3% vs 6.9%; P < .001) and higher rates of positive circumferential resection margins (8.3% vs 5.2%; P = .001). On multivariate analysis, radiation fractionation was not significantly associated with overall survival.

Conclusions: SCRT is used for only approximately 1% of patients treated preoperatively for nonmetastatic rectal cancer in the United States. The results of recently completed randomized trials may further inform patterns of practice in the United States and abroad.