Stereotactic Body Radiation Therapy for Oligoprogressive Pleural Mesothelioma: Fine-Tuning the Optimal Doses

There is growing evidence of a role of stereotactic body radiation therapy (SBRT) in the treatment of patients with oligoprogressive pleural mesothelioma (PM). The objective of this study was to investigate the optimal radiation therapy doses and schedules in this setting. The records of patients treated with SBRT (>5 Gy per fraction) for oligoprogression of PM at 2 institutions from June 2014 to September 2022 were reviewed. Patients were divided into 2 groups: "intermediate-dose" SBRT (i-SBRT; total dose, 30-36 Gy in 5-6 fractions) and "high-dose" SBRT (h-SBRT; total dose, 45-50 Gy in 4-8 fractions). The comparison between the 2 groups in terms of local control (LC) and toxicity was the primary endpoint of the study. Overall, 23 patients were treated for 25 pleural lesions. All had received upfront chemotherapy with platinum/pemetrexed. Fifteen patients were treated with i-SBRT and 8 patients with h-SBRT. The median equivalent dose was 40 Gy (range, 40-49.6) in the i-SBRT group and 74.46 Gy (range, 64-88) in the h-SBRT group. Six-month, 1-year, and 2-year LC were 100%, 100%, and 80% in the i-SBRT group and 100%, 100%, and 67% in the h-SBRT group, respectively (p =.94). Only 2 patients (1 for each dose group) had a recurrence in the radiation therapy field, both after experiencing a distant relapse. No severe acute and late toxicities were observed in the i-SBRT group, whereas in the h-SBRT group, 2 patients experienced G2 acute and late thoracic pain and 1 patient experienced G2 acute and G3 chronic thoracic pain. In our experience, SBRT is a safe and effective option for selected patients with oligoprogressive PM. Use of intermediate total doses keeping the dose per fraction high seems to offer an excellent LC, avoiding the risk of severe toxicity.