The impact of radiation dose on chemoradiation outcomes and rectum preservation in locally advanced rectal cancer: A retrospective study

Dose-escalated neoadjuvant chemoradiation can be safely achieved using modern radiation techniques. We analyzed the clinical complete response (cCR) and rectum preservation rates at different dosages. This retrospective study was conducted at a medical center and included patients with non-metastatic rectal adenocarcinoma who received neoadjuvant chemoradiation at different dosages (45, 50, and 55 Gy) between 2012 and 2020. Total 137 patients with nonmetastatic rectal cancer were analyzed. The cCR rates of the 45, 50, and 55 Gy groups were 8.2%, 9.8%, and 37%, respectively (p = 0.003). Patients in each group who underwent rectum-preserving procedures (local excision and watch-and-wait approach) were 4.1%, 3.3%, and 22.2%, respectively (p = 0.011). Compared to patients receiving 55 Gy, those treated with 45 Gy or 50 Gy demonstrated significantly lower odds of achieving cCR. The odds ratios (ORs) were 0.151 (95% confidence interval [CI]: 0.042-0.547, p = 0.004) for 45 Gy and 0.185 (95% CI: 0.059-0.585, p = 0.004) for 50 Gy. Additionally, rectum preservation odds were significantly lower in the 45 Gy (OR, 0.142, 95% CI: 0.026-0.764, p = 0.023) and 50 Gy (OR, 0.113, 95% CI: 0.021-0.606, p = 0.011) compared to the 55 Gy group. None of the patients in 55 Gy group experienced grade 3 or higher toxicity related to pelvic radiation. The overall survival rates were not different in 3 groups (p = 0.109). The multivariable analysis found different doses of pelvic radiation as the only significant factor improving the cCR rate. Dose-escalated neoadjuvant chemoradiation of 55 Gy achieved a significantly higher cCR rate, potentially facilitating rectum-preserving procedures without compromising overall survival.