MRI Simulation-guided Boost in Short-course Preoperative Radiotherapy for Unresectable Rectal Cancer

Improvements in downstaging are required when using preoperative chemoradiation for unresectable rectal cancer. There is therefore a need to explore more effective schedules. The study arm will receive MRI simulation-guided boost in short-course preoperative radiotherapy followed by consolidation chemotherapy , which may enhance the shrinkage of tumor comparing with the concurrent chemoradiation.

The study is a prospective phase II randomized multicenter trial. The purpose of this study is to compare short-term radiotherapy with MRI simulation-guided boost followed by consolidation chemotherapy(Experimental group) with preoperative long-term chemoradiotherapy(Control group) for middle-lower unresectable locally advanced rectal cancer evaluated by MRI. The primary endpoint is the rate of R0 resection and cCR, and the secondary objectives are local recurrence-free survival, distant metastasis-free survival, disease-free survival and overall survival at 3-year and 5-year follow up. Furthermore, pathological complete response rate, the acute and late toxicity profile and quality of life (QOL) after 3 years follow-up are secondary endpoints. The exploratory end point includes the circulating tumor DNA, and other potential biomarkers from tumor tissue and blood sample for treatment response and survival predicting. For each group, a plan for collection of serum/plasma/feces at baseline and different stages during or after treatment and for obtaining fresh tumor tissue for freezing prior to treatment was defined in the protocol. The SUNRISE-trial has been designed by National Cancer Center/Cancer Hospital, Chinese Academy of Medical Sciences, Peking Union Medical College, and the hypothesis is R0 resection rate in Experimental group was superior to that in Control group. Interim analysis design: As a phase II trial, the safety of experimental intervention is a major concern. We took the toxicity data from STELLAR, a phase III randomized study led by our center, as a reference. The incidence of G3 and above side effects in the short course radiotherapy with sequential neoadjuvant chemotherapy group was 28%, and that in the standard long-course concurrent chemoradiotherapy control group was 5%. Considering that boost dose may increase toxicity, if severe toxicity in the study group significantly exceeds that in the control group by more than 35%, it is up to the principal investigator to decide whether to modify the study protocol or terminate the study. The sample size of the interim analysis was calculated by the Z-pooled test, with α=0.05 (one-sided test), 1-β=0.90, using PASS 11 software. The frequency of the toxicity of G3 and above should be compared when neoadjuvant therapy was completed in 21 patients enrolled in each group.