How 18F rhPSMA-7.3 PET/MRI Imaging Can Help Detect Biochemically Recurrent Prostate Cancer and Inform Treatment Planning

For patients with biochemically recurrent (BCR) prostate cancer (PCa) who have previously received a prostatectomy, ¹⁸F rhPSMA-7.3 (rhPSMA) PET/MRI imaging could potentially serve as a “one-stop shop,” both for detecting BCR PCa and tailoring radiation therapy (RT) treatment options.

A recent phase II pilot study conducted by Devaki Shilpa S. Surasi, MD, and colleagues of The University of Texas MD Anderson Cancer Center assessed men with PCa who underwent rhPSMA PET on a simultaneous 3T PET/MRI scanner, post-prostatectomy.

The researchers hypothesized that rhPSMA PET/MRI would “accurately detect recurrent PCa to direct field design in salvage RT planning even at low PSA levels.” Their primary goal was to measure the positive predictive value (PPV) of rhPSMA PET/MRI in detecting PCa, with a secondary aim of measuring RT plan changes after rhPSMA PET/MRI and treatment responses.

The study enrolled 29 patients between August 2021 and January 2023. All patients received at least six months of hormonal therapy (HT), in addition to standard fractionated RT. Of them, 28 underwent rhPSMA PET/MRI imaging. Prior to surgery and upon diagnosis of PCa, the Gleason score was ≥7 and the median prostate-specific antigen (PSA) level was 7.0 ng/mL (IQR: 0.9-29.5). rhPSMA-positive findings were detected in 20 patients (71%), four of whom sought treatment elsewhere and elected not to receive follow-up scans.

Of the remaining 16 patients who received a follow-up scan, one result was found to be a false positive.

In addition, of the 28 patients who underwent PET/MRI imaging, the RT plan was changed for 22 individuals. Eight patients experienced major changes to their plan, including “extension of clinical target volumes to cover PSMA-positive pelvic lesions or cancellation of RT due to polymetastatic disease.” Nine patients experienced minor plan changes, such as “dose escalation to gross disease or dose de-escalation to the rest of prostate fossa.” Five patients experienced both major and minor changes to their RT plans.

After treatment, patients with a positive scan returned six to 18 months later for second timepoint PET/MRI imaging. Those who received both RT and HT were found to have a complete response on the second timepoint scan, and in the time between treatment and the second scan, the median PSA was <0.1 ng/mL (IQR: <0.1-0.1).

The researchers concluded that simultaneous rhPMSA PET/MRI scans resulted in a high rate of disease detection, even at low PSA levels. In addition, implementation of this imaging strategy led to changes in 79% of patients’ RT plans, supporting the use of this strategy in categorizing treatment for patients with BCR PCa.

Source: International Journal of Radiation Oncology, Biology, Physics