Efficacy and safety of MR-guided adaptive simultaneous integrated boost radiotherapy to primary lesions and positive lymph nodes in the neoadjuvant treatment of locally advanced rectal cancer: a randomized controlled phase III trial

In locally advanced rectal cancer (LARC), optimizing neoadjuvant strategies, including the addition of concurrent chemotherapy and dose escalation of radiotherapy, is essential to improve tumor regression and subsequent implementation of anal preservation strategies. Currently, dose escalation studies in rectal cancer have focused on the primary lesions. However, a common source of recurrence in LARC is the metastasis of cancer cells to the proximal lymph nodes. In our trial, we implement simultaneous integrated boost (SIB) to both primary lesions and positive lymph nodes in the experimental group based on magnetic resonance-guided adaptive radiotherapy (MRgART), which allows for more precise (and consequently intense) targeting while sparing neighboring healthy tissue. The objective of this study is to evaluate the efficacy and safety of MRgART dose escalation to both primary lesions and positive lymph nodes, in comparison with the conventional radiotherapy of long-course concurrent chemoradiotherapy (LCCRT) group, in the neoadjuvant treatment of LARC.