Metamodeling of late rectal bleeding in patients undergoing radiotherapy for prostate cancer.

61Background: Predictive models for late rectal bleeding (LRB) after radiotherapy (RT) for prostate cancer were established by several studies, with good performance on development population (POP). Nonetheless, they were found to be unsatisfactory in their generalization to independent validation cohorts. Aim of the study is to build a metamodel for grade 2-3 (G23) and grade 3 (G3) LRB (LENT/SOMA) starting from literature evidence and to validate it on a new POP. Methods: The metamodel was constituted by clinical/dosimetric features and by their coefficients. Available predictive models for LRB were selected by literature search. Models including rectal Equivalent Uniform Dose (EUD) with/without patient-related dose-modifying factors were retrieved. The process allowed identification of “evidence-based” clinical/dosimetric features associated to LRB. Coeff. for identified features were resolved by weighted mean of published values, using their standard deviation as weight and then inserted in a sigmoid-s...