Predictors of Local Control With Palliative Radiotherapy for Multiple Myeloma.

Introduction: We performed a retrospective analysis of patients with multiple myeloma (MM) receiving palliative radiotherapy (RT) and assessed factors associated with local control, with a focus on dose/fractionation and cytogenetics.

Materials and methods: We included patients who received palliative RT for MM at our institution. Cytogenetics were collected via fluorescence in situ hybridization. Follow-up imaging was used to assess local control.

Results: A total of 239 patients with 362 treated lesions were included. Eighty-six (36.0%) patients had high-risk cytogenetics. Most lesions received 20 Gray (Gy) in 5 fractions (131, 36.2%), 8 Gy in 1 fraction (93, 25.7%), or 30 Gy in 10 fractions (48, 13.3%). At a median follow-up of 4.3 years, 4-year local progression was 13.4% (95% confidence interval [CI]: 10.3-17.5). No cytogenetic abnormalities were correlated with local progression, nor were double- and triple-hit status. There was a nonsignificant trend toward association between number of treated lesions and local progression (HR for >3 vs. 1: 2.43 [95% CI: 0.88-6.74], P = .059). Among patients with >3 treated lesions, equivalent dose in 2 Gy fractions ≥20 Gy reduced progression (HR: 0.05 [95% CI: 0.01-0.23], P = .0001).

Conclusion: In this large study of patients with MM, modern palliative RT achieved excellent rates of long-term local control. Although there was no dose-response observed in the overall cohort, patients with high volume symptomatic disease may benefit from EQD2 ≥20 Gy. High-risk cytogenetics did not appear to influence radioresponsiveness, and standard radiation doses appear to be effective for all MM patients regardless of cytogenetics.