Stereotactic body radiotherapy for bone metastases in patients with colorectal cancer

To clarify the clinical outcomes of stereotactic body radiotherapy for colorectal cancer-derived bone metastases and identify factors predicting treatment failure.

Patients treated with stereotactic body radiotherapy for bone metastases from colorectal cancer between September 2013 and June 2019 were retrospectively reviewed. The prescribed dose for spine and non-spine bone metastases was 24 Gy in two fractions and 35 Gy in five fractions, respectively. The end point was local failure, which was defined as tumour progression on imaging evaluations. In addition, various treatment- and tumour-specific factors were evaluated to determine predictors of local failure.

This study included 43 lesions in 38 patients, with solitary bone metastases in 18 lesions (42%), re-irradiation stereotactic body radiotherapy in 28 lesions (65%) and postoperative stereotactic body radiotherapy due to spinal cord compression in 10 lesions (23%). The median follow-up after stereotactic body radiotherapy was 12 (range, 2-60) months. The 1-year LF rate was 44%. In the univariate analysis, sacral metastases (P = 0.02) were found to be significantly correlated with LF, and multiple-course systemic therapy before stereotactic body radiotherapy (P= 0.06) and large target volume (P = 0.07) showed a trend towards an association with LF. However, these factors were not independent predictors of LF in the multivariate analysis.

More than 40% of the lesions treated with stereotactic body radiotherapy for bone metastases from colorectal cancer showed LF within 1 year. No poor prognostic factors could be identified statistically. The poor outcomes in all groups indicate that the treatment intensity of the stereotactic body radiotherapy was insufficient to control colorectal cancer bone metastases.