Implications for Radiation Microboosting Based on Pathology Correlations With Prostate-Specific Membrane Antigen and Multiparametric Magnetic Resonance Imaging Findings

<h2>Abstract</h2><h3>Introduction</h3> Prostate-specific membrane antigen (PSMA) PET and multiparametric MRI (mpMRI) are used to contour the dominant intraprostatic lesion (DIL) when incorporating a microboost. However, it is unclear how well PSMA and mpMRI findings correlate with the true pathologic DIL. So, we performed an analysis between preoperative imaging and the final surgical specimen to identify predictors of discordance. <h3>Methods</h3> This was a single-center retrospective analysis of patients with prostate cancer who underwent PSMA imaging prior to prostatectomy between January 2022 and December 2023. PSMA lesions were independently contoured and measured by a reviewer blinded to the final pathology. mpMRI reports were reviewed for lesion number, location and size. Lesion size and hemigland location on imaging were compared to final pathology. Associations between concordance or discordance and patients' demographics and clinicopathological characteristics were examined. <h3>Results</h3> Of the 48 patients included, mean (SD) PSA was 13.9 (± 12.9), 40% had grade group 4/5 disease, and 58% were staged as pT3 or higher. The pathologic DIL matched the hemigland of the largest PSMA/mpMRI lesion in 94/90% of cases, respectively. The median maximum lesion diameter size discrepancy between PSMA and mpMRI and final pathology was 3.4 mm (IQR 16.3-24.8) and 4 mm (IQR 3-9), respectively. PSMA and mpMRI underestimated lesion size in 59% and 64% of cases, respectively. On PSMA, higher PSA and lower biopsy grade group were associated with greater imaging/pathology size discrepancy on both univariate and multivariable analysis (after adjusting for SUVmax); on mpMRI, higher PSA was associated with greater imaging/pathology size discrepancy on both univariate and multivariable analysis (after adjusting for PI-RADS score; p<0.05). <h3>Conclusion</h3> Standard treatment margins may either over or underestimate the extent of the true gross disease, depending on individual tumor characteristics. Further research is needed to develop a standardized framework for using PSMA and mpMRI to guide microboosting.