Introduction/Background Published studies quote up to 19.7% of patients treated with radical pelvic radiotherapy (RT) develop pelvic insufficiency fractures (PIF) post-treatment. We hypothesize that the risk is greatest in patients with low bone mineral density (BMD) prior to starting RT, and this could be estimated from the planning CT data.

Methodology We identified 23 patients treated with radical RT for cervical cancer who developed PIF confirmed on imaging. These patients were matched 1:2 to age-stratified controls (nonPIF) who received similar treatment. Hounsfield units (HU) were measured on radiotherapy planning scans using Eclipse treatment planning software, for L2/L4 and L5 vertebral bodies and S1 and S2 vertebrae. HU measurements of the trabecular bone were then converted to quantified CT measurements (qCT) using the equation qCT=17.8+(0.7xHU). T-test for unequal variance was used to assess for statistical difference between the 2 cohorts, with 2-tailed significance testing taken as p≤0.05.

Results The 2 cohorts were well matched for age (median 58 years nonPIF vs 59 years PIF) and for BMI (26.5 for nonPIF vs 26 for PIF). There was a consistent trend toward lower measurements of Hounsfield units and calculated qCT values for the PIF group compared to the nonPIF group. The differences reached statistical significance for measurements of sacral bones (see table 1). In the PIF group 96% (22/23) of PIFs were in the sacrum.

Conclusion Pelvic radiotherapy increases the risk of PIFs which can impact on quality of life. The planning CT scan can provide data to help identify patients who are at higher risk. This could allow preventive measures post RT to be considered such as lifestyle advice and bone protection agents.