PET/CT imaging with gallium-68 (Ga-68) prostate-specific membrane antigen (PSMA-11) could help in the early detection and treatment of recurrent prostate cancer after a patient undergoes radical prostatectomy, according to a study in the February issue of the Journal of Nuclear Medicine.
Researchers from the U.S. and Germany believe PSMA-PET/CT could help direct salvage radiotherapy in the 20% to 80% of patients who experience a biochemical recurrence of the disease within 10 years of radical prostatectomy.
Currently, salvage radiotherapy is the main option for treatment; however, imaging modalities often are not sensitive enough to identify the location of recurrence until it is too late. Making the situation more difficult is the lack of clearance for PSMA-PET/CT by the U.S. Food and Drug Administration (FDA).
Lead author Dr. Jeremie Calais, from the University of California, Los Angeles (UCLA), and colleagues believe that PSMA-PET/CT is sufficiently sensitive to locate the recurrent prostate cancer early enough to possibly guide salvage radiotherapy or direct patients to the most appropriate follow-up treatment.
The international, multicenter study included 270 patients from UCLA, the Technical University of Munich, the Ludwig Maximilian University of Munich, and the University of Essen. The subjects had a recurrence of prostate cancer after radical prostatectomy but had not received prior radiotherapy. PSMA-PET/CT was performed at a serum prostate-specific antigen (PSA) level of less than 1 ng/mL (JNM, February 2018, Vol. 59:2, pp. 230-237).
"The first sign of prostate cancer recurrence is a rising PSA," Calais explained in a statement from the Society of Nuclear Medicine and Molecular Imaging (SNMMI). "For salvage radiotherapy to be successful, it should be initiated before the PSA rises above 1 ng/mL, and ideally, closer to 0.2 ng/mL or lower."
The researchers found that 132 patients (49%) had a positive PSMA-PET/CT result, and 52 (19%) had at least one PSMA-positive lesion outside of the consensus clinical target volume (CTV). The two most common PSMA-PET-positive lesion locations outside the consensus radiation fields were in the bone (23, 44%) and perirectal lymph nodes (16, 31%).
"Salvage radiotherapy is only curative if recurrent disease is completely encompassed by the radiotherapy fields," Calais said. "Therefore, in almost 20% of these patients, the addition of PSMA-PET/CT would have a potentially major impact on the outcome of salvage radiotherapy."
The researchers believe that PSMA-PET/CT will eventually become part of the standard of care for prostate cancer patients with biochemical recurrence. They recommended a randomized imaging trial of salvage radiotherapy with or without PSMA-PET/CT to investigate its effects on treatment outcome.