mpMRI shows higher detection than PSMA PET/CT

By Agata Buczak

A post‑hoc analysis in men with prostate cancer (PC), published in Radiotherapy and Oncology, conducted within a prospective phase 2 study of extreme hypofractionated salvage radiotherapy, found that multiparametric MRI (mpMRI) detects more local recurrent lesions than prostate-specific membrane antigen (PSMA) PET/CT with biochemical failure after radical prostatectomy.

Giuseppe Sanguineti (IRCCS Regina Elena National Cancer Institute, Rome, Italy) and colleagues evaluated 107 consecutive patients with biochemical failure after radical prostatectomy who underwent restaging with both mpMRI and PSMA PET/CT.

In the paired comparison, mpMRI identified local disease in a significantly greater proportion of patients, while PSMA PET/CT “missed about 1/3 of patients” that were positive on mpMRI. This difference remained even when limiting the analysis to patients imaged with 18F-PSMA rather than 68Ga-PSMA.

The authors noted that PSMA PET/CT detected most of the local lesions also identified on mpMRI, stating that “the added value of PSMA PET/CT to local restaging with mpMRI is minimal.”

Overall, 68 of 107 patients (63.5%) harbored at least one lesion in the prostatic fossa. Among these 68 patients, lesions were detected by mpMRI alone in 24 patients, by PSMA PET/CT alone in four patients, and by both imaging modalities in 40 patients.

The discordance rate between the two imaging tests was 41.2% (28/68; p<0.001). When restricting the population to the 91 patients scanned with 18F‑PSMA, detection rates remained significantly higher for mpMRI (61.5%) than for PSMA PET/CT (46.2%; p=0.004).

Lesion‑level analysis showed that PSMA PET/CT “failed to detect smaller lesions,” whereas mpMRI tended to miss lesions with lower SUVmean values. Lesion location in the prostatic fossa did not affect detectability for either modality.

mpMRI identified extraprostatic pelvic disease in 10.3% of patients, compared with 17.8% on PSMA PET/CT. PSA at restaging independently predicted local lesion detection for both imaging modalities.

Although the imaging review was not blinded, the authors note that “the usefulness of blinding has been questioned in studies with an objective outcome such as the feasibility of contouring a discrete lesion in the prostatic fossa as in the present one.”

Despite this limitation, the authors conclude that “mpMRI should be considered the preferred diagnostic modality to local restaging though PSMA PET/CT is complementary for extraprostatic staging.”

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