Multi-centre technical evaluation of the radiation-induced lymphocyte apoptosis assay as a predictive test for radiotherapy toxicity.

•The RILA assay is the leading candidate biomarker for radiotherapy toxicity.•We describe work to standardise its use across multiple centres.•Patient factors including smoking and arthritis were found to affect RILA score.•RILA predicts acute breast pain but not other acute end-points.•This work establishes the basis for implementing the assay clinically.