Optimum Timing for Surgery After Pre-operative Radiotherapy 6 vs 12 Weeks

The aim of this study is to determine whether greater rectal cancer downstaging and regression occurs when surgery is delayed to 12 weeks after completion of radiotherapy/chemotherapy compared to 6 weeks. Hypothesis: Greater downstaging and tumour regression is observed when surgery is delayed to 12 weeks after completion of CRT compared to 6 weeks.本研究旨在明确：相较于在放化疗完成后6周施行手术，若将手术延迟至放化疗完成后12周，是否可使直肠癌获得更显著的肿瘤降期与肿瘤退缩。 研究假说：相较于放化疗（CRT）完成后6周行手术，将手术延迟至放化疗完成后12周时，可观察到更显著的肿瘤降期与肿瘤退缩。