Feasibility study of dose de-escalation in postoperative intensity-modulated radiation therapy for locally advanced thymoma.

Purpose: This study aimed to investigate retrospectively the feasibility of reducing the standard postoperative radiation therapy (PORT) dose of 45-50 Gy for locally invasive thymoma to shorten treatment duration and minimize side effects, while preserving disease-specific survival (DSS) and progression-free survival (PFS).

Materials and methods: Between January 2016 and June 2022, 150 locally advanced thymoma patients underwent surgery followed by intensity-modulated radiation therapy, with a median follow-up of 40.8 months; the standard regimen was 45-50 Gy in 25 fractions (median biological effective dose [BED] 60 Gy), compared to a de-escalation regimen of 30-35 Gy in 10 fractions (median BED 47.25 Gy), with PFS as the primary endpoint, and overall survival (OS), DSS, and toxicity as secondary endpoints.

Results: No significant differences were found between standard and de-escalation groups in 3-year PFS (p = 0.406), with both groups achieving 100% 3-year DSS; two deaths in the de-escalation group were due to double primary cancers. All locoregional recurrences occurred outside the radiation field. Factors including age, initial tumor size, myasthenia gravis, and pathological type showed no correlation with PFS or OS. No grade II toxicities occurred in the de-escalation group, whereas the standard group had three cases of grade II toxicity, specifically radiation pneumonitis.

Conclusion: Radiation dose de-escalation in locally advanced thymoma patients undergoing PORT showed comparable survival outcomes with reduced toxicity and shorter treatment duration, but requires longer follow-up to confirm efficacy and safety.