Making a Subjective Notion Computer-Interpretable: The Case of the Tumour-Volume to Breast-Volume Ratio for the Surgical Decision of Breast Cancer

Clinical practice guidelines (CPGs) often include ambiguous criteria making their translation as computer-interpretable guidelines a difficult task. In breast cancer management, whether to perform a breast conservative surgery (BCS) or not is one example. Most international CPGs recommend to perform a BCS when the tumour volume / breast volume ratio allows for good cosmetic results, which cannot be directly translated into a computable format. We propose to compute an estimate of the ratio using the maximum size of the tumour to compute the tumour volume and the bra size to compute the breast volume. In addition, we take into account the location of the tumour according to quadrants and unions of quadrants. The model has been tested on a retrospective sample of 34 clinical decisions of a breast cancer unit in a Parisian university hospital (France). Concordance was found in 91.2% of the cases, with good sensibility and specificity. This finding could set a new pathway to advance on the development of actionable decision criteria to be used in a future clinical decision support system for breast cancer management.