Adaptive Boost Radiotherapy to Primary Lesions and Positive Nodes in the Neoadjuvant Treatment of Locally Advanced Rectal Cancer

"The choice of adaptive protocol and delivery system is based on individual tumor characteristics, patient anatomy and institutional capabilities. This approach provides flexibility in treatment planning while adhering to evidence-based dose constraints. Adaptive radiotherapy is delivered using one of the following advanced platforms: the Elekta Unity MRI Linac (MR-guided) or Varian Ethos (CBCT-guided), or the United Imaging uRT-linac 506c (FBCT-guided).~ART Option 1 (simultaneous integrated boost, SIB):~GTVp+GTVn: A total dose of 60-65 Gy delivered in 25 fractions using a simultaneous integrated boost approach.~CTV: A total dose of 45-50 Gy delivered in 25 fractions.~ART Option 2 (sequential boost, SB) GTVp+GTVn: An initial hypofractionated boost with a total dose of either 9-12 Gy delivered in 3 fractions or 10 Gy delivered in 2 fractions.~CTV: Followed by standard fractionation delivering 45-50 Gy in 25 fractions."

Conventional long-course radiotherapy administered in a non-adaptive manner without dose escalation. Treatment will be targeted to the pelvic lymphatic drainage region only. A total dose of 45-50 Gy will be delivered in 25 fractions over the course of treatment.

Capecitabine (825 mg/m2, po, twice daily)

Following the completion of concurrent chemoradiotherapy, consolidation chemotherapy will commence 7 to 10 days later. Patients will receive two cycles of the CAPEOX regimen. Each cycle comprises: Capecitabine: 1.0 g/m² administered orally twice daily on days 1 through 14, and Oxaliplatin: 130 mg/m² administered intravenously on day 1.

Total mesorectal excision surgery