Predicting the benefit of stereotactic body radiotherapy of colorectal cancer metastases.

Aim: To evaluate Stereotactic body radiotherapy (SBRT) in metastatic colorectal cancer (mCRC) and identify the benefit of the treatment by using a predictive algorithm.

Methods: 85 patients treated with SBRT for mCRC were retrospectively analyzed. The CLInical Categorical Algorithm (CLICAL©) was used to predict probability of relapse after SBRT. Variables pre-SBRT were tested for significance for time to relapse (TTR). The patients' CLICAL© score was the mean of sub-scores of each significant variable's effect on the endpoint. Patients with similar scores were grouped into four signatures dependent on level of benefit after SBRT.

Results: Median age was 69 years (42-88), 63 % had a performance status 0 and 47 % were treated for a single metastasis. At the time of the analysis, 90 % had relapsed (95 % out-of-field). Median TTR was 7.3 months (4.6-8.5), and the 2-year relapse-free rate was 15 % (95 %CI = 7-22). The CLICAL© signature III-IV predicted a low risk of relapse if receiving high dose SBRT to all metastases or to lung metastases only. Signature I-II had a short TTR, why SBRT for these patients was judged non-beneficial.

Conclusion: The benefit from SBRT varies among mCRC patients. CLICAL© may serve as a screening tool for SBRT referrals but needs to be validated.