Diagnostic value of Gallium-68 prostate specific membrane antigen positron emission tomography/computed tomography method in determining treatment response in patients with prostate cancer and in patient management

Aim: In our retrospective study, we aimed to investigate the correlation of quantitative values obtained from Gallium-68 prostate specific membrane antigen (Ga-68 PSMA) positron emission tomography/computed tomography (PET/CT) imaging with biochemical response in prostate cancer and their potential contribution to evaluating treatment response. Materials and methods: 40 patients who underwent Ga-68 PSMA PET/CT imaging before and after treatment and whose total prostate specific antigen (tPSA) values were available were examined.In the pre-treatment imaging, one target lesion with the highest intensity from the metastatic lesion areas was determined. SUVmax, SUVmean, PSMA tumor volume (PSMA-TV) and total lesion PSMA (TL-PSMA) values of the prostate gland and target lesions were recorded in pre- and post-treatment imaging.Percentage changes after treatment in the tPSA values of the patients and the quantitative values of the lesions were calculated.Spearman correlation analysis was used to evaluate the relationships between quantitative variables.Wilcoxon test was used to compare quantitative values.A value of p<0.05 was considered statistically significant. Results: The age range of the patients was 53-84 years, and the mean age (±sd) was 69±7 years. The tPSA values of the patients were between 0.824-8211 ng/ml before the treatment and 0.003-504.9 ng/ml after the treatment.While the percentage change in tPSA values of the patients did not show a significant correlation with the percentage changes in SUVmax, SUVmean, PSMA-TV values of the prostate gland and lymph nodes, it showed a moderate correlation with the percentage changes in the same parameters of the bone lesions.Percentage change in tPSA values was correlated with low (R=0.445; p=0.006), moderate (R=0.500; p=0.014) and strong (R=0.700; p=0.004) significant correlations with percentage change in prostate gland TL-PSMA values, lymph node TL-PSMA values and bone lesions TL-PSMA values, respectively.In 16/40 patients with PSMA receptor expression only in the prostate gland and no evidence of metastasis, the percentage change in tPSA was strongly correlated (R=0.711; p=0.002) with the percentage change in prostate gland TL-PSMA values.The change in the quantitative values of the lesions and tPSA values after treatment was statistically significant (p<0.001 for tPSA). Conclusion: In prostate gland and lymph nodes TL-PSMA, in bone lesions, especially TL-PSMA, SUVmax, SUVmean, PSMA-TV parameters have potential importance in evaluating treatment response with Ga-68 PSMA PET/CT.Our findings need to be confirmed by prospective studies with large patient groups. Key Words: Prostate Cancer, PET scan, Prostate specific antigen, treatment response