3612 - Local and Distant Recurrences Following Palliative Radiation for Multiple Myeloma

Purpose/Objective(s): Palliative radiation for pain is a common treatment for multiple myeloma (MM), with patients often requiring multiple courses of radiation. This study evaluated distant and local recurrence rates following a range of palliative radiation dose/fractionation regimens and examined whether recurrence rates were associated with high-risk cytogenetics.

Materials/Methods: Patients receiving radiotherapy (RT) for MM in a multi-site hospital system between 2018 and 2023 were included. Patients without bone marrow confirmation of MM were excluded. Data were collected on patient demographics, RT regimens, sites and techniques, and cytogenetics (CG). High-risk CG included FGFR3/IGH fusion or t(4;14), MAF/IGH fusion or t(14;16), IGH/MAFB fusion or t(14:20), TP53 (17p) deletion, and 1q amplification. Re-irradiation of a previously treated site and a second course of radiation to a new site were used as surrogates for local and distant treatment failure.

Results: 116 patients were included (median age of 66 years, IQR 16; 51.7% male). The following initial dose/fractionation regimens were used: 20 Gy in 5 fractions (n=65; 56.0%), 30 Gy in 10 fractions (n=15; 12.9%), 8 Gy in 1 fraction (n=10; 8.6%), 24 Gy in 8 fractions (n=10; 8.6%), other conventional regimens (n=10; 8.6%), or stereotactic body RT (SBRT) (n=6; 5.2%). Most patients (n=94; 84.8%) received AP/PA or 3D radiation. Intensity-modulated RT (IMRT) or SBRT was used in the minority of cases (n=22; 15.2%). Only 4 patients (3.4%) experienced local treatment failure, while 46 patients (39.7%) developed distant recurrence requiring RT. Of patients who had local or distant recurrence requiring more than one course of RT, 22% had high-risk CG. Of those who required only one course of RT, 27% had high-risk CG. Neither the initial RT regimen nor high-risk CG was associated with a statistically increased risk of local or distant recurrence.

Conclusion: In conclusion, local control rates were high (96.6%) even with single fractions of radiation, but nearly 40% of patients required subsequent courses of radiation for distant recurrence. There was no association with recurrence and high-risk CG. These results suggest that a range of palliative dose/fractionation regimens for multiple myeloma are similarly effective at maintaining local control, and that opportunity exists for standardizing dose/fractionation regimens for myeloma even within a single institution.