Stereotactic body radiation therapy for oligo-progressive 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 oligo-progressive pleural mesothelioma (PM). The objective of this study was to investigate the optimal RT doses and schedules in this setting.The records of patients treated with SBRT (> 5 Gy per fraction) for oligo-progression of PM at two Institutions from June 2014 to September 2022 were reviewed. Patients were divided in two 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 two groups in terms of local control (LC) and toxicity was the primary endpoint of the study.Overall, 23 patients were treated on 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 (EQD2) 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=0.94). Only two patients (one for each dose group) had a recurrence in the RT field, both after experiencing distant relapse. No severe acute and late toxicities were observed in the i-SBRT group, while in the h-SBRT group 2 patients experienced a G2 acute and late thoracic pain and one patient developed a G2 acute and G3 chronic thoracic pain.In our experience, SBRT is a safe and effective option for selected patients with oligo-progressive PM. Use of intermediate total doses keeping the dose per fraction high seems to offer an excellent LC, avoiding the risk of severe toxicity.