Explaining relationships between local dose and rectal toxicity in prostate cancer radiotherapy with voxel-based population analysis.
Résumé
Intensity Modulated Radiotherapy (IMRT) allows delivering of highly conformal dose to complex targets, implying nevertheless the choice of optimal constraints for the organs at risk (OAR) with the aim of reducing toxicity. To estimate the risk of toxicity, current predictive models stand on the dose-volume histograms (DVH) whose main drawback is the lack of spatial accuracy as they consider the organs as a whole volume and thus ignore the heterogeneous intraorgan radio-sensitivity. A framework for finding relationships between local dose and toxicity is proposed here. In this approach, the planned dose distributions are registered together on a common coordinate system and compared across a population at a voxel level, thereby allowing the highlighting of 3D anatomical patterns which may be in part responsible of toxicity. We demonstrated here the value of the approach by explaining rectal toxicity in prostate cancer radiotherapy (PCRT). 116 patients with 31 month median follow-up were considered. They received a total dose of 80 Gy in the prostate by IMRT. When analyzing rectal toxicity, significant difference of dose was found in large regions within the anterior wall close to the prostate (1cm). This promising voxel-wise approach allowed the highlighting of regions that may be involved in rectal toxicity.