PSMA PET reveals uneven prostate-bed recurrence after prostatectomy

PSMA PET imaging revealed an uneven distribution of prostate-bed recurrences after radical prostatectomy, with the bladder-neck and vesicourethral anastomotic regions containing the largest shares of mapped events and the ventral perivesical region containing comparatively few. In the retrospective cohort, 63 patients had 92 anatomically distinct prostate-bed recurrences. Four lesions extended across more than one anatomical zone, producing 97 lesion-zone events. The bladder-neck region, designated Zone 3, accounted for 28 events, or 28.9%, while the vesicourethral anastomotic region, Zone 2, accounted for 21 events, or 21.6%. Together, these observations provide imaging-based evidence for evaluating postoperative prostate-bed clinical target volume, or CTV, definitions against established radiation-oncology guidelines.

The research combined a multicenter contouring exercise with a retrospective recurrence-mapping analysis. Ten radiation oncologists from eight centers independently delineated the prostate-bed CTV in one postoperative case. Agreement was summarized using the Dice similarity coefficient, or DSC, and the 95th-percentile Hausdorff distance, or HD95. The mean pairwise DSC was 0.767 ± 0.046, and the mean HD95 was 8.244 ± 2.347 mm. The investigators reported considerable interobserver variation, particularly around the bladder. Because the exercise involved a single postoperative case, the measurements characterize agreement for that case rather than the full anatomical and clinical variation encountered in routine practice.

For the recurrence analysis, the investigators assigned PSMA PET-positive prostate-bed lesions to an exploratory framework containing six anatomical zones. In addition to the bladder-neck and vesicourethral anastomotic regions, the retrovesical area, Zone 5b, contained 17 of 97 events, or 17.5%, and the dorsolateral perivesical region, Zone 5a, contained 12 events, or 12.4%. The cranial seminal-vesicle-bed region, Zone 6, contained seven events, while the ventral perivesical region, Zone 4, contained only two of 97 events, or 2.1%. The observed maximum extents were 1.3 cm for the 12 Zone 5a events and 3.0 cm for the seven Zone 6 events. These figures describe the extent of recurrence observed in this sample; they do not establish universally safe CTV boundaries or predict recurrence patterns in all patients after surgery.

The researchers also assessed whether recurrence centroids were covered by CTV definitions from the ESTRO-ACROP 2023, GFRU 2020, and RTOG 2010 guidelines. At the patient level, all identified recurrence centroids were covered in 54 of 63 patients by ESTRO-ACROP, or 85.7% (95% confidence interval, 75.0%–92.3%). Coverage was 52 of 63 patients, or 82.5% (95% confidence interval, 71.4%–90.0%), for GFRU and 53 of 63 patients, or 84.1% (95% confidence interval, 73.2%–91.1%), for RTOG. These results are centroid-based assessments and therefore do not demonstrate that every portion of every recurrence was contained within the corresponding CTVs.

Overall, the study found that PSMA PET-positive recurrences were unevenly distributed within the prostate bed after radical prostatectomy and that radiation oncologists showed notable variation when contouring postoperative targets. The low event count in the ventral perivesical region provides an imaging-based rationale for further evaluation of CTV boundaries in that area, while the contouring results underscore the variation around the bladder. The findings may help inform future studies of postoperative target-volume refinement, but the authors emphasized that validation in larger multicenter cohorts is required. The study did not test whether changing any guideline boundary would improve clinical outcomes, and the contouring exercise and retrospective recurrence analysis do not establish a causal effect of CTV size on recurrence or treatment success.

Subject of Research: Postoperative prostate-bed recurrence mapping and radiation target-volume delineation

Article Title: PSMA PET recurrence mapping and guideline coverage after radical prostatectomy: implications for postoperative prostate bed CTV delineation

Article References: Qi, X., Zhang, H., Chen, C., Wu, J., Liao, X., Zhang, J., He, L., Lu, N., Shen, Y., Wang, H., Zhong, Q., Li, Y., Zhang, M., Gao, X., & Li, H. (2026). PSMA PET recurrence mapping and guideline coverage after radical prostatectomy: implications for postoperative prostate bed CTV delineation. BMC Medical Imaging. https://doi.org/10.1186/s12880-026-02931-x

Image Credits: AI Generated

DOI: 10.1186/s12880-026-02931-x

Keywords: PSMA PET, prostate cancer, radical prostatectomy, prostate bed, recurrence mapping, salvage radiotherapy, clinical target volume, radiation oncology, interobserver variation, guideline coverage, PSMA, recurrence