Pelvic insufficiency fractures –a late effect of radiotherapy

Abstract

Keywords, late effects, pelvic radiotherapy Introduction: Pelvic insufficiency fractures are stress fractures caused by normal or physiological stress on weakened bone . Radiotherapy increases the risk of insufficiency fractures in patients(1). These fractures are underdiagnosed in younger women. Presenting symptoms include pelvic and back pain of which can substantially affect quality of life. Aim- To evaluate the characteristics of patients with pelvic insufficiency fractures following radiotherapy Methods: Four patients presented to pelvic late effects clinic between Jan-June 2019, with confirmed sacral insufficiency fractures on diagnostic magnetic resonance imaging (MRI). Radiotherapy technique 4 field brick 3D CRT (n=1), volumetric modulated arc therapy (VMAT) (n=3), 1 of these with a library of 3 adaptive plans. All patients had concurrent weekly cisplatin. Dose prescribed 50Gy/25# (n=2) and 45Gy/25# (n=2). All Ca Cervix patients had 4 Brachytherapy insertions (24Gy) and Ca Endometrium patient had no insertions. All patients presented with lower back pain. Retrospective planning CT dosimetric analysis, by delineation of the sacrum in Eclipse V15.5 (Varian Medical Systems,Palo Alto). A structure was created using boolean operator to define sacrum overlap with PTV. Dose volume histograms were exported for the sacrum structure and planning characteristics recorded. Results: Age range of patients was 32-73. Radiotherapy complete between Feb 2013-June 2018 for Ca Cervix (n=3) stages 2B (n=2), 11b2 (n=1) and Ca Endometrium grade 3 1B(n=1). 2 patients were pre-menopausal on hormone replacement therapy (HRT) with 2 remaining patients on no HRT. Time to confirmed diagnosis of insufficiency fractures from radiotherapy completion was mean 13 (4-26) months. The mean sacrum volume was 149.6cm3 (130.97-186.61). The mean sacrum overlap with PTV volume was 35.99 cm3 (30.73-40.75). The max dose to the sacrum was 53.27Gy and minimum 16.22Gy. The mean D50% of the sacrum was 40.24Gy (38.69-44.98) and mean D40% 42.91Gy (39.29-74.77). Conclusion/Discussion: The dose-effect relationship has been defined with a 22% risk of fracture at 35Gy and 45% at 40Gy for D50%(2). Our patients D50% were all above 35Gy. Dose received from Brachytherapy has not been accounted for. There is potential using dosimetric analysis to identify patients at high risk of fractures. Numerical