TOPLINE:

In patients with biochemical failure after prostatectomy, about two thirds showed detectable local disease at restaging. Multiparametric MRI alone detected local lesions in over one third of patients vs only 5.9% with prostate-specific membrane antigen (PSMA) PET-CT alone.

METHODOLOGY:

• Up to 50% of patients with prostate cancer have biochemical failure or prostate-specific antigen (PSA) persistence after primary surgery. Guidelines recommend PSMA PET-CT for restaging when salvage radiotherapy is being considered, but whether PET-CT and multiparametric MRI perform similarly in detecting local recurrence is unclear. This study prospectively compared the two modalities in patients with early post-prostatectomy biochemical failure.
• Researchers evaluated 107 consecutive patients with pT2-3 pN0-x prostate cancer who were referred for salvage radiotherapy after surgery at a single institution, with inclusion restricted to those with biochemical failure and PSA levels between 0.2 and 2.0 ng/mL.
• Patients underwent both multiparametric MRI of the pelvis and PSMA PET-CT imaging within 8 weeks of each other. The scans were read by two experts; the modalities were co-registered, and lesions were contoured for comparison. Lesions were considered to be the same across modalities if the centroids of the respective lesions were within 1 cm of each other. Most patients (n = 91, 85%) underwent PET-CT with ¹⁸F-PSMA.

TAKEAWAY:

• Overall, 68 patients (63.5%) had at least one lesion in the prostatic fossa. The two modalities together had a detection rate of 58.8%; MRI alone was far superior to PSMA PET-CT alone in detecting local lesions (35.3% vs 5.9%).
• The percentage of discordant pairs was higher than expected (28 of 68, 41.2%), and agreement between the two modalities was only moderate (Cohen kappa coefficient, 0.49; P < .001).
• Of 78 local lesions, 45 (57.7%) were detected by both tests, 29 (37.2%) by MRI only, and four (5.1%) by PSMA PET-CT alone. For lesions detected by both tests, the relative centroid distance for lesion pairs never surpassed 10 mm — indicating that lesions seen via both modalities were the same ones.
• The mean PSA level at restaging was 0.53 ng/mL. Patients with MRI-positive findings had a significantly higher mean PSA level at restaging than those with MRI-negative findings (0.61 vs 0.41 ng/mL; P = .008). Detection on PSMA PET-CT was independently associated with a higher PSA level at restaging and the type of tracer used. The probability of detecting local disease was significantly higher with ¹⁸F-PSMA than with ⁶⁸Ga-PSMA (46.2% vs 12.5%; P = .012).

IN PRACTICE:

“PSMA PET/CT and multiparametric MRI showed significantly different local detection rates, with the former missing about one third of patients who tested positive at the latter one,” the authors of the study wrote. “Moreover, the difference between multiparametric MRI and PSMA PET/CT was mitigated but not eliminated by using ¹⁸F-PSMA instead of ⁶⁸Ga-PSMA.” They conclude that MRI “should be considered the preferred diagnostic modality [for] local restaging, though PSMA PET/CT is complementary for extraprostatic staging.”

SOURCE:

The study, led by Giuseppe Sanguineti, MD, IRCCS Regina Elena National Cancer Institute, Rome, Italy, was published online in Radiotherapy and Oncology.

LIMITATIONS:

The two main limitations of the study were the lack of pathologic validation of local findings and the absence of blinding in reviewing imaging results.

DISCLOSURES:

The study did not receive any specific funding, and the authors declared having no conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.