RR Myelo POINT: A Retrospective Single-Center Study Assessing the Role of Radiotherapy in the Management of Multiple Myeloma and Possible Interactions with Concurrent Systemic Treatment

SIMPLE SUMMARY: Currently, few papers have been published regarding the possible interactions between radiotherapy and systemic agents for the treatment of multiple myeloma. In this paper, we retrospectively analyze the data from 312 patients (577 lesions) who received radiotherapy at our institution from 2005 to 2020, with the aim of clarifying the clinical impact of radiotherapy dose and concurrent systemic treatment (CST). The safety profile of the radiotherapy was excellent; high biologically effective doses (BEDs) and CST were associated with higher toxicity rates at the end of radiotherapy, but not after one and three months. The pain control rate was 87.4% at the end of treatment and further increased at three and six months. Radiological progression was reported only for 4.4% of the lesions at six months (based on the data available for 181 lesions) and was significantly more frequent for lesions treated without CST or BED < 15 Gy. ABSTRACT: Background and purpose: Although chemotherapy, biological agents, and radiotherapy (RT) are cornerstones of the treatment of multiple myeloma (MM), the literature regarding the possible interactions of concurrent systemic treatment (CST) and RT is limited, and the optimal RT dose is still unclear. Materials and methods: We retrospectively analyzed the records of patients who underwent RT for MM at our institution from 1 January 2005 to 30 June 2020. The data of 312 patients and 577 lesions (treated in 411 accesses) were retrieved. Results: Most of the treated lesions involved the vertebrae (60%) or extremities (18.9%). Radiotherapy was completed in 96.6% of the accesses and, although biologically effective doses assuming an α/β ratio of 10 (BED 10) > 38 Gy and CST were significantly associated with higher rates of toxicity, the safety profile was excellent, with side effects grade ≥2 reported only for 4.1% of the accesses; CST and BED 10 had no impact on the toxicity at one and three months. Radiotherapy resulted in significant improvements in performance status and in a pain control rate of 87.4% at the end of treatment, which further increased to 96.9% at three months and remained at 94% at six months. The radiological response rate at six months (data available for 181 lesions) was 79%, with only 4.4% of lesions in progression. Progression was significantly more frequent in the lesions treated without CST or BED 10 < 15 Gy, while concurrent biological therapy resulted in significantly lower rates of progression. Conclusion: Radiotherapy resulted in optimal pain control rates and fair toxicity, regardless of BED 10 and CST; the treatments with higher BED 10 and CST (remarkably biological agents) improved the already excellent radiological disease control.