Comparative study between Ga-prostate-specific membrane antigen positron emission tomography and conventional imaging in the initial staging of prostate cancer.

Introduction: The management of prostate cancer has undergone significant advances since the introduction of Ga-prostate-specific membrane antigen ( Ga-PSMA) positron emission tomography (PET) scans. Data on the use of Ga-PSMA PET scans in the setting of biochemical recurrence is widely available. Data on the use of Ga-PSMA PET as an initial staging modality, however, is limited. The aim of this retrospective study was to compare the staging of patients with newly diagnosed prostate cancer between Ga-PSMA PET and current conventional imaging modalities. The potential impact of any change in stage will be analysed.

Methods: Details of all patients who underwent Ga-PSMA PET in South Australia between March 2016 and March 2017 were obtained. One hundred and thirty-one patients with newly diagnosed prostate cancer who had Ga-PSMA PET prior to consideration of definitive treatment were included in this study. The stage pre- Ga-PSMA PET (based on conventional imaging) and post- Ga-PSMA PET was recorded. The stage was classified as A - localised disease, B - presence of regional lymphadenopathy, C - oligometastatic disease (up to three metastases) and D - widespread metastases. Management plans were recorded.

Results: This study showed that the use of Ga-PSMA PET resulted in a change of stage in 37 (28%) patients with an upstage in 17 (13%) patients and a downstage in 20 (15%) patients (P < 0.001). Ga-PSMA PET excluded oligometastatic disease in 11 (8%) patients who had suspicious oligometastatic disease based on a single conventional imaging modality. These Ga-PSMA PET findings impacted on management in at least 24 (18%) patients.

Conclusion: The use of Ga-PSMA PET scans in initial staging can have a significant impact on staging and management when compared to current conventional imaging modalities.