PURE-MRI: An international study assessing physician accuracy in delineating the prostate and urethra on prostate MRI

Precise delineation of genitourinary structures during prostate cancer (PCa) care is critical to optimize treatment delivery while minimizing toxicity and injury. The Prostate and UREthra on MRI (PURE-MRI) study is an international, prospective study to assess physicians' accuracy segmenting prostate and urethra on MRI.

Physicians who diagnose or treat PCa were invited to contour prostate and urethra on patient cases using standard T₂-weighted MRI (all planes). We compared these contours to reference consensus segmentations produced by a multidisciplinary panel of experts. We also evaluated performance of validated auto-segmentation AI tools. Accuracy was assessed with spatial and volumetric analyses. A mixed effects model was used to evaluate potential factors influencing contour performance.

62 specialists from 11 countries created 114 prostate and 110 urethra contours. Prostate median (min, max) accuracy for physicians [vs. AI] was Dice score: 0.92 (0.62, 0.95) [vs. 0.95 (0.94, 0.96)], maximum deviation inside prostate: 3.4 mm (1.0, 12.4) [vs. 3.0 mm (3.0, 3.0)], maximum deviation beyond prostate: 5.3 mm (2.4, 17.3) [vs. 3.9 mm (3.1, 4.9)], mean deviation (per case) from the reference prostate: 1.6 mm (0.9, 3.9) [vs. 1.2 mm (1.1, 1.6)]. Urethra accuracy was Dice score: 0.33 (0.03, 0.69) [vs. 0.41 (0.35, 0.48)], coverage: 36 % (3 %, 96 %) [vs. 81 % (80 %, 91 %)], maximum (2D) deviation beyond urethra: 1.6 mm (1.0, 2.3) [vs. 1.7 mm (1.3, 2.1)].

Physicians contour the prostate on MRI with overall Dice score >0.90, though typical cases still include at least one error >5 mm and sometimes >10 mm. Physician urethra contours were less accurate, with typical coverage of <40 % of the reference urethra (compared to >80 % for AI). Physician trainees performed similarly to experienced clinicians. AI tools give comparable accuracy to practicing physicians for prostate contours and achieve better coverage of the urethra.