Validation of T2- and diffusion-weighted magnetic resonance imaging for mapping intra-prostatic tumour prior to focal boost dose-escalation using intensity-modulated radiotherapy (IMRT).

•5 mm mapping prostate biopsies correlated with imaged intra-prostatic tumour.•Diffusion-restricted tumour of ≥0.5 cm3 can be dose-escalated with confidence.•Tumours of <0.5 cm3 should not be dose-escalated.•Diffusion-weighted MR has good diagnostic accuracy for dominant tumour lesions.