The following is a summary of “Prostate-specific membrane antigen-based imaging for stereotactic irradiation of low-volume progressive prostate cancer: a single-center experience,” published in the August 2023 issue of Oncology by Varga et al.
Prostate-specific membrane antigen (PSMA), a transmembrane protein, can appear on prostate cancer (PC) cell surfaces. Researchers performed a retrospective study to investigate the use of PSMA-based imaging to improve the accuracy of target definition and delivery of stereotactic body radiotherapy (SBRT) in patients with locally recurrent or oligometastatic PC.
The study analyzed the data from 363 examinations. Inclusion criteria comprised of confirmed PC with indications of recurrence. Imaging was done through 99mTc-PSMA-I&S single-photon emission computed tomography (SPECT)/CT or 18F-JK-PSMA-7 positron emission tomography/computer tomography (PET/CT). Scan assessment and tumor volume marking were done in Nuclear Medicine. Target volume delineation on topometric CT was performed in Oncotherapy. Volumes were compared through image fusion and registration.
Of the 363 PSMA isotope-based examinations, 84 lesions in 64 patients received SBRT treatment. For intermodality comparison, 70 lesions from 50 patients were evaluated. The PSMA-defined target volume was significantly smaller than the TCT-defined tumor size: GTVCT(gross tumor volume on the TCT) (27.58 ± 46.07 cm3) versus BTVPSMA(biological target volume on the PSMA-based examination) (16.14 ± 29.87 cm3). Geometric analysis revealed a Dice similarity coefficient (DSC) of 0.56 ± 0.20 (0.07-0.85).
Prostate-specific antigen (PSA) control assessed treatment response as initial PSA averaged 16.98 ng/ml (± SD: 33.81), dropping to 11.19 ng/ml (± SD: 32.85) three months after SBRT. Post-therapy PSMA imaging at three months showed reduced or halted isotope uptake in 14 cases. In 65.6% of all cases, conventional imaging control indicated 22 (52.4%) complete remissions, 14 (33.3%) partial remissions, four (9.5%) stable diseases, and two (4.8%) progressive diseases.
The study concluded that PSMA-based imaging shows promise in stage specification and detecting minor progression. These findings indicated that the hybrid approach can impact treatment choices and SBRT target definition.