Based on preliminary findings on the motion error of the clinical target volume (CTV) in MR-guided adaptive radiotherapy (MRgART) for locally advanced rectal cancer (LARC), this study aims to reduce CTV-to-PTV margins and evaluate the complete response (CR) rate following MRgART in LARC patients. Additionally, it will investigate the safety and tolerability of MRgART, as well as its impact on:
3-year organ preservation rate
Local recurrence rate in patients under a "watch-and-wait" approach
3-year overall survival (OS), disease-free survival (DFS), and local progression-free survival (LPFS).
Furthermore, by analyzing ADC maps of the gross tumor volume (GTV), this study will characterize treatment responses and spatial deformation in metabolically active tumor subregions. These insights may inform future dose-escalation strategies for LARC radiotherapy, with the ultimate goal of improving prognosis and quality of life in this patient population.