P-138: Real World Single Centre Experience On The Use of Radiotherapy In The Treatment of Patients with Multiple Myeloma

Introduction: Radiotherapy (RT) has traditionally played an important role in the management of patients with multiple myeloma (MM). Recent advances in treatment have led to a prolonged survival advantage. In this context, there is limited recently published data on the use of RT in MM. We analyse real-world patterns of RT use to evaluate the relevance of this treatment modality in the era of novel therapies.

Methods: We identified patients with MM who received RT at our tertiary care centre between 2016 and 2023. Using electronic patient records we collected demographic, disease-related and RT-related data for individual patients.

Results: 157 patients out of 905 who were reviewed in our outpatient clinic were treated with RT. Median age at diagnosis was 59 years, 62.4% of patients were male and 51% were white. 17.8% had high risk cytogenetic features and 12.7% had ISS stage III disease. Median number of treatment lines was 4 (range 1-9) with 90.7% of patients exposed to bortezomib, 84.1% lenalidomide, 47.7% pomalidomide, 34.4% daratumumab, 30.5% ixazomib, 20.5% carfilzomib, 13.2% isatuximab, 12.6% belantamab, and 2.6% CAR-T/bispecific antibodies (BsAbs). 76.8% of patients underwent at least 1 ASCT.

We observed 331 episodes of RT within our patient cohort, with a median of 2 RT episodes per patient (range 1-9). 28% of the cohort received RT at the time of initial diagnosis. Type of tissue irradiated included bone (67.1%), bone/paramedullary (22.1%) and extramedullary soft tissue plasmacytomas (10.9%). The spine was the most irradiated site (39.6%) followed by the pelvis/sacrum (14.5), femur/tibia (8.2%) and skull/facial bones (8.2%). The mean dose of RT was 16.6Gy (range 6-45Gy), the median number of fractions was 5, and the most frequently used dosing schedule was 20Gy given over 5 fractions. Indications for RT included palliation of bone pain (66.2%), spinal cord compression (16.3%), post-operative consolidation (6.3%), prophylaxis/treatment of pathological fracture (5.4%), and extramedullary disease requiring ‘debulking’ (5.7%).

8.5% of RT episodes involved delivery of RT to a site which had previously been irradiated, due to later same-site relapse. RT did not affect haemopoietic stem cell (HSC) yield in those who underwent HSC collection; in patients without prior RT the mean HSC yield was 5.15x10⁶ vs 4.30x10⁶ in those who did require prior RT (t test, p=0.158).



Conclusions: This single centre study involving patients on contemporary treatment protocols showed that RT was used mainly at subsequent therapy lines rather than at diagnosis and was predominantly used as a pain relief measure. An important observation was the low incidence of repeat irradiation at previous RT sites, suggesting the radiosensitive nature of MM. RT could continue to hold a role in patients who become refractory to systemic therapy as salvage bridging therapy especially in the era of CAR-T and BsAbs. More focussed studies on the timing of radiotherapy in the treatment pathway are warranted to maximise its use.