Adaptive radiotherapy of locally advanced sigmoid colon cancer with intra‑fractional motion using the MRIdian system: A case report

Neoadjuvant chemotherapy, when combined with radiotherapy, serves as an optional treatment for patients locally advanced sigmoid colon cancer and is usually performed in conjunction complete mesocolic excision. The substantial movement of surrounding organs cases frequently leads to toxicity normal tissues. present report details the case a 76‑year‑old man diagnosed cancer. Initially, using Tomotherapy Hi‑Art system was selected; however, during image guidance from first sixth fractions, tumor location underwent marked change, exceeding range planning target volume. Efforts recapture were unsuccessful, leading decision transition patient MRIdian daily online adaptive radiotherapy. positional variations evident each system, mean shifts 2.58 cm right‑left direction, 1.24 cranial‑caudal direction 0.40 anterior‑posterior direction. time entry completion 41 min. Adaptive plans all 19 two treatments repeated due moving out tracking range. Following irradiation gross volume decreased by 62%. Notably, experienced no side effects treatment. A CT scan conducted 3 months after radiotherapy revealed reduction size, consistent partial response, scheduling surgery. surgery, 6 local recurrence surgical bed region. findings support feasibility implementing plan context neoadjuvant chemoradiotherapy.