The clinical utility of total-body [ Ga]Ga-PSMA-11 PET/CT in prostate cancer: identifying extra-regional bone metastases and informing treatment strategies.

[BACKGROUND AND PURPOSE] Bone metastasis significantly impacts morbidity and mortality in prostate cancer patients, necessitating accurate detection and monitoring. Although [ Ga]Ga-PSMA-11 PET/CT imaging provides superior sensitivity compared with conventional imaging, the conventional field of view (CFOV; skull to proximal femur) obtained with short axial field of view (SAFOV) PET/CT scanners may underestimate the extent of disease. This study aimed to evaluate the prevalence and characteristics of bone metastases outside the CFOV scan range (distal to the proximal one-third of the femur) using total-body [ Ga]Ga-PSMA-11 PET/CT imaging and its impact on tumor burden, staging and subsequent treatment in prostate cancer patients.

[METHODS] This retrospective study included 1211 prostate cancer patients who underwent total-body [ Ga]Ga-PSMA-11 PET/CT imaging. Imaging results were independently evaluated by three nuclear medicine physicians. Positive findings were validated through histopathology, treatment response, prostate-specific antigen (PSA) changes, or follow-up imaging. We further characterized the clinical and imaging characteristics of lesions located beyond the CFOV scan range. We also assessed the impact of total-body imaging on tumor burden biomarkers (PSMA-TV and TL-PSMA) and disease staging, and constructed a nomogram to predict the risk of extra-CFOV lesions.

[RESULTS] Apart from bone metastases, total-body [ Ga]Ga-PSMA-11 PET/CT imaging did not identify any other types of lesions outside the CFOV scan range. Among the 1211 patients, 5.12% (62 patients) had bone metastases outside the CFOV scan range. Multivariable regression analysis revealed that patients in the castration-resistant prostate cancer (CRPC) stage, with higher Gleason scores (≥ 8), and higher PSA levels (≥ 12.57 ng/mL) were independent predictors of bone metastases outside the CFOV scan range. We developed a nomogram to predict bone metastases outside the CFOV scan range, in which the patient's disease stage demonstrated greater predictive value than the Gleason score and PSA level. In the subset of 62 patients with lesions outside the CFOV scan range, tumor burden metrics were significantly increased (P < 0.001). Treatment plans were altered in 20 patients (32.3% of the subgroup; 1.65% of the total cohort).

[CONCLUSIONS] SAFOV PET/CT scanners with CFOV scan range may underestimate the true extent of bone metastasis. Total-body scan range using total-body PET/CT scanners revealed occult bone metastases in 5.12% of patients, particularly in those with higher PSA, Gleason scores, and CRPC stage. This extended view significantly impacts tumor burden quantification, leads to disease upstaging, and influences treatment planning. The developed nomogram can guide clinicians at centers with SAFOV PET/CT scanners in identifying patients who would most benefit from extended field-of-view imaging.