Preoperative chemoradiotherapy with concomitant small field boost irradiation for locally advanced rectal cancer: A multi-institutional phase II study (KROG 04-01)

PURPOSE: This study was designed to determine the effect of concomitant small field boost irradiation given during preoperative chemoradiotherapy for patients with locally advanced rectal cancer. METHODS: The study prospectively enrolled 38 patients scheduled for preoperative chemoradiotherapy. Pelvic radiotherapy of 43.2 Gy/24 fractions was delivered and boost radiotherapy of 7.2 Gy/12 fractions was concomitantly administered during the latter half of the pelvic radiotherapy treatment period. Two cycles of a bolus 5-fluorouracil and leucovorin injection in the first and fifth weeks of radiotherapy were administered. The median time to surgery after completion of chemoradiotherapy was six weeks. Tumor responses to chemoradiotherapy were assessed by using magnetic resonance volumetry and postchemoradiotherapy pathology tests to determine tumor downstaging and tumor regression rate. RESULTS: Thirty-six of 38 patients (94.7 percent) underwent the scheduled surgery. The mean tumor volume reduction rate was 70.3 percent, and the clinical response rate was 66.7 percent. The downstaging rates were 41.7 percent for T classification, 85.2 percent for N classification, and 72.2 percent for stage. Tumor regression grades after preoperative chemoradiotherapy were Grade 1 in 5 patients (13.9 percent), Grade 2 in 24 patients (66.7 percent), Grade 3 in 3 patients (8.3 percent), and Grade 4 in 4 patients (11.1 percent). Ten patients (26.3 percent) experienced ≥ Grade 3 acute toxicity. CONCLUSIONS: Our data suggest that concomitant boost irradiation does not improve clinical outcomes compared with other published preoperative chemoradiotherapy regimens. In addition, the clinicians choosing to use concomitant small field boost irradiation should be cautious to minimize the risk of unplanned sphincter ablation.