LAUSR

BACKGROUND Radiotherapy-related insufficiency fractures (RRIFs) represent a common, burdensome consequence of pelvic radiotherapy. Their underlying mechanisms remain unclear and data on the effect of osteoporosis are contradictory, with limited studies assessing BMD by DXA. METHODS BMD by DXA (Hologic) scan and fracture risk (FRAX) following pelvic RRIF were retrospectively assessed in 39 patients (median age 68 years), at a tertiary cancer centre. Patient characteristics and treatment history are presented narratively; correlations were explored using univariate regression analyses. RESULTS Additional cancer treatments included chemotherapy (n=31), surgery (n=20), brachytherapy (n=19). Median interval between initiation of radiotherapy and RRIF was 11 [7.5-20.8] and between RRIF and DXA 3 [1-6] months. Three patients had normal BMD, 16 had osteopenia and 16 osteoporosis, following WHO classification. Four patients were <40 years at time of DXA (all Z-scores>-2). Median 10-year risk for hip and major osteoporotic fracture were 3.1% [1.5-5.7] and 11.5% [7.1-13.8], respectively. Only 33.3% of patients had high fracture risk (hip fracture >4% and/or major osteoporotic >20%), and 31% fell above the intervention threshold per NOGG guidance (2017). Higher BMD was predicted by lower pelvic radiotherapy dose (only in L3, L4), concomitant chemotherapy and higher body mass index. CONCLUSION At the time of RRIF, most patients did not have osteoporosis, some had normal BMD, and overall had low fracture risk. Whilst low BMD is a probable risk factor, it is unlikely to be the main mechanism underlying RRIFs and further studies are required to understand the predictive value of BMD.