Diabetes increases the risk of serious adverse events after re-irradiation of the spine

Introduction: In this study we investigate the risk of radiation-induced serious adverse event of the spine in a large cohort of consecutive retreated patients with palliative radiotherapy (RT) for metastatic cancer in the spine.

Methods and materials: From 2010 to 2014, 2387 patients received spinal irradiation with a palliative intent for metastatic spinal cord compression at our institution. The patients were reviewed for prior RT and 220 patients had received re-irradiation of the spine. Clinical and treatment data were obtained from the patients' records and the RT planning system.

Results: Patients had metastatic disease from breast, prostate, lung, hematological or other cancers (22.7%, 21.8%, 21.4%, 3.2% and 30.9%, respectively). Median follow-up was 99 days. Median cumulative EQD2 was 57.6 Gy₂; range: 20.0-90.0 Gy. Spinal events related to re-irradiation were observed in fourteen patients; six patients were diagnosed with radiation-induced myelopathy (RIM) and nine patients with radiation-induced vertebral fracture (RIF). In a multivariate analysis, diabetes was related to increased risk of toxicity (HR = 7.9; P = 0.003).

Conclusion: The incidence of RIM and RIF (6 and 9 out of 220 patients, respectively) was low in our cohort of re-irradiated patients. Patients with diabetes had a higher risk of adverse events which should be considered before re-irradiation of the spine.