Exploring the use of preoperative MRI for assessing the anatomical location of positive surgical margin at robot-assisted radical prostatectomy (RARP)

Purpose: Robot-assisted radical prostatectomy (RARP) is an effective treatment for localized prostate cancer (PCa), but positive surgical margins (PSMs) occur in up to 22% cases. This study quantifies the relationship between the tumor location on preoperative MRI and PSM location on final pathology examination. Material and methods: We retrospectively reviewed PCa patients who underwent both prostate MRI and RARP between January 1, 2022 and December 31, 2022. The RARP specimens were divided into 14 regions, and concordance between MRI-detected lesions (PIRADS > 2) and PSM locations was assessed. Results: Data from 464 patients revealed PSMS in 130 (28%) patients, totaling 187 PSMs. Concordance between tumor and PSM location was found in 152 PSMs (81%). Of these, 38% corresponded with a T3 lesion on MRI, and 72% showed pathological T3 at the PSM location. Most PSMs (46%) were at the apex. The median size was 6.0 mm (IQR 1.9–10.3). In contrast, 19% of PSMs were in regions without MRI-detected lesions, mainly located at the apex (43%) and bladder neck (29%). In this group, 34% had no positive biopsy on the corresponding side. PSMs in this group showed pathological T3 in 66% of cases. The median size was 3 mm (IQR 2.5–7.0 mm), and 46% had a pathological ISUP Gleason score ≥ 2. Conclusion: This study highlights the role of preoperative MRI assessment in predicting PSM locations during RARP. In 81% of cases, PSMs corresponded to MRI-detected lesions (PI-RADS > 2), suggesting that MRI can help by guiding surgical planning and potentially reduce PSM rates.