Volumetric 68 Ga-PSMA PET/CT analysis of bone metastasis subtypes in prostate cancer: correlation with prostate-specific antigen and International Society of Urological Pathology grade.

[OBJECTIVE] The aim of this study was to determine the rate of metastasis types in prostate cancer (PCa) patients with bone metastasis and to evaluate the relationship between volumetric parameters obtained from gallium-68 ( 68 Ga) prostate-specific membrane antigen (PSMA) PET/computed tomography (CT) and prostate-specific antigen (PSA) levels.

[MATERIALS AND METHODS] We retrospectively reviewed the images of patients who underwent 68 Ga-PSMA PET/CT for restaging for recurrent PCa between 2014 and 2019. All detected bone lesions were manually grouped as 'osteoblastic (OB), osteolytic (OL), mixed (M), and radio-occult (RO) lesions' and the number and percentage were determined. Different volumetric values are obtained for each type of bone metastasis using the LIFEx v7.3.0 program. The relationship between PSA level and these volumetric values will be determined by the Spearman correlation test. The relationship between the International Society of Urological Pathology (ISUP) PCa grade group and volumetric values will be evaluated by the Kruskal-Wallis correlation test.

[RESULTS] Seventy-one patients had a total of 599 bone metastasis. Of these lesions, 268 were OB (44.7%), 39 were OL (6.5%), 72 were M (12.0%), and 220 were RO (36.7%). Total lesion volume (TLV) (P : 0.001), total lesion activity (TLA) (P : 0.001), and OB-TLA (P : 0.042) were significantly different between ISUP grades. In addition, the total number of lesions showed a statistically significant difference between ISUP grades (P : 0.019). PSA level correlated with RO lesion number ( r : 0.404, P : 0.016), RO-TLV ( r : 0.471, P : 0.004), and RO-TLA ( r : 0.528, P : 0.001).

[CONCLUSION] 68 Ga-PSMA PET/CT can identify the source of biochemical recurrence by detecting RO lesions at early stages when bone mineral density is not affected.