Involve-site Radiotherapy Combined With Chemotherapy and Immunotherapy as Neoadjuvant Treatment for Locally Advanced Rectal Cancer

A dose of 25 Gy in 5 fractions was delivered as short-course radiotherapy, with one fraction per day, completing treatment within one week. The target volume was delineated using both CT and MRI. Compared to conventional radiotherapy fields, the irradiated volume was significantly reduced to include only the primary tumor and any metastatic lymph nodes as identified on MRI and CT.

After completion of radiotherapy, chemotherapy with the XELOX regimen (oxaliplatin 130 mg/m² on day 1 plus capecitabine 1500 mg/m² on days 1-14, every 3 weeks) was initiated in combination with sintilimab immunotherapy (200 mg every 3 weeks) for 4 cycles.

"Patients in the standard short-course radiotherapy group will receive 25 Gy in 5 fractions, once daily. Target volumes will be delineated according to the 2023 Guidelines for Target Volume Delineation and Planning of Rectal Cancer (National Cancer Center/National Cancer Quality Control Center), including the primary tumor, mesorectal region, and internal iliac and obturator lymph node drainage areas."

Patients in the standard long-course radiotherapy group will receive 50 Gy in 25 fractions, once daily, five days per week, with concurrent oral capecitabine chemotherapy. Target volumes will be delineated according to the 2023 Guidelines for Target Volume Delineation and Planning of Rectal Cancer (National Cancer Center/National Cancer Quality Control Center), including the primary tumor, mesorectal region, and internal iliac and obturator lymph node drainage areas.

Two weeks after the completion of radiotherapy, patients will receive four cycles of CAPOX chemotherapy.