MRI-guided stereotactic radiotherapy for oligometastatic peritoneal carcinomatosis: toward integrative oncologic approaches.

AIMS: Peritoneal carcinomatosis (PC) is historically linked to poor prognosis. In oligometastatic cases, combining systemic treatments with locoregional therapies like stereotactic body radiotherapy (SBRT) may improve outcomes. Magnetic resonance-guided radiotherapy (MRIgRT) enables online adaptation (OA), optimizing daily dose distribution based on patient anatomy. This study assesses the feasibility and efficacy of MRIgSBRT in PC patients treated at a single institution. MATERIALS AND

METHODS

Clinical and dosimetric data from consecutive PC patients treated with MRIgSBRT were analyzed. Feasibility and acute and late toxicity using the CTCAE 5.0 scale were evaluated. Secondary endpoints included 2-year local recurrence-free survival (LRFS), progression-free survival (PFS), and overall survival (OS), assessed using Kaplan-Meier method and Cox regression analysis. Complete response (CR) and partial response (PR) defined the objective response rate (ORR), while ORR or stable disease (SD) defined clinical benefit (CB).

RESULTS

Thirty-four oligometastatic PC patients (51 lesions) were treated with MRIgSBRT from July 2019 to December 2023. Median PTV dose was 35 (10–50) Gy in 5 (2–5) fractions (BEDα/β=10 75.35). OA was used in 76.2% of 227 fractions. CR, PR, and SD were observed in 62.7%, 11.8%, and 9.8% of lesions, respectively, resulting in an 84.3% CB rate. At 19 months’ median follow-up, 2-year LRFS, PFS, and OS rates were 82%, 20%, and 93%, respectively. BEDα/β=10 ≥ 90 Gy improved LRFS (p = 0.0085). No acute or chronic toxicity of any degree has been reported.

CONCLUSION

MRIgSBRT was effective and well tolerated in PC patients, enabling dose escalation while sparing healthy tissue.