Bone insufficiency fractures after pelvic radiotherapy are reported to have a low incidence and delayed onset when assessed on CT scans. Our aim was to determine the prevalence of pelvic insufficiency fractures (PIFs) after chemoradiotherapy (CRT) for cervical cancer (CxCa) on MRI follow-up, noting time of onset, symptoms, interval to healing and ADC values on diffusion MRI scans.

In our institution, locally advanced CxCa patients undergo external beam RT (45-50Gy, 25#) including the sacral alar, cervix brachytherapy (24-28Gy, 4#) and weekly Cisplatin. They are followed up with serial MRI pelvis at 3, 12 and 24 months post-treatment. 20 consecutive women were retrospectively reviewed by an oncologic radiologist for the presence of PIFs, defined by linear low T1W and high STIR signal intensity. Features were graded for severity according to displacement, multiplicity, extent of bone oedema. ADC values were measured at the sites of fracture; when no fracture was seen, ADC was measured in the sacral alar. Correlations with symptoms was performed.

15 patients had 55 MRI scans (7 pre- and 48 post-treatment), average follow-up 22 months. 12/15 patients were aged over 50. 13/15 were staged as 2B. 9/15 patients had PIFs, majority diagnosed at 3 months (8/9 patients), 1 at 12 months. PIFs were graded as mild-1, moderate-5 or severe-3. 25 fracture sites were identified (18 sacral, 3 pubic, 1 iliac, 1 acetabular, 2 L4-5). Mean ADC values were 731 um2/s (204-1482) for all visible sacral fractures and 177 um2/s (33-499) for non-fractured sites (MW Test: p<0.001). Healing occurred at 5/25 fracture sites (in 6-23 months), with only 1 patient showing healing of all affected sites. 2 patients had related bone pain. 2 patients with PIFs sustained displaced pelvic fractures after falls. Only 1 patient had pelvic tumour recurrence at 12 months (no PIF).

PIFs on MRI are common after CRT for locally advanced CxCa, with an early onset post-treatment. Majority of patients are asymptomatic, but might have increased risk of displacement after trauma. Further research will be done into radiation dose distribution/techniques and any correlation with bone changes.

PIFs are common on MRI follow-up after CRT for CxCa. Although mostly asymptomatic, only 20% healed during follow-up, with 2/15 patients suffering displaced pelvic fractures after minor trauma.