The role of Ga68 PSMA PET/CT imaging in Lu177 PSMA treatment planning in metastatic castration-resistant prostate cancer.

OBJECTIVE: Lutetium-177 (Lu177) prostate-specific membrane antigen (Lu177 PSMA) is a novel targeted treatment for patients with metastatic castration-resistant prostate cancer (CRPC). The purpose of the study was to determine the molecular volumetric Gallium-68 (Ga68) PSMA PET/CT parameters that can predict patients who will respond to treatment. METHODS: These single-center retrospective data were obtained from metastatic CRPC patients receiving intravenous 6.0-8.5 GBq Lu177 PSMA treatment every 6-8 weeks for a maximum of 3-8 cycles, with baseline Ga68 PSMA PET/CT scan, clinical data, and information on treatment responses. All lesions were divided into two groups according to the increase and decrease in PSMA expression levels of 600 bone lesions and 85 lymph nodes that were compatible with metastasis of 23 patients after the treatment. The primary endpoint of our study was the evaluation of the relation between the baseline SUVmax, PSMA TV, TL PSMA values, and the treatment response of the two groups. The threshold values were determined for the parameters that had significant relations. In the present study, the prostate-specific antigen (PSA) response and treatment-induced toxicities were also evaluated as the secondary endpoint. RESULTS: It was found that SUVmax, PSMA TV, and TL PSMA values in bone metastases showed significant differences between the groups with decreased and increased PSMA expression levels after the treatment. The AUC value for SUVmax was significant (AUC = 0.677; p < 0.001). The cutoff value was > 10.50 (sensitivity = 91.8%, Specificity = 41.5%) for SUVmax, > 1.50 cm3 (sensitivity = 49.1%, specificity = 70%) for PSMA TV and > 8.50 g (sensitivity = %60.9, specificity = %72.2) for TL PSMA. The median SUVmax value before the treatment in all metastatic lymph nodes was found to be 7.1 (5.4-12.4), and the median SUVmax after the treatment was 2.5 (1.6-12.1) (p < 0.001). CONCLUSION: It was shown in the present study that Lu177 PSMA treatment response may be higher in CRPC patients with metastatic bone lesion with high baseline PSMA expression level, and better treatment response may be achieved in patients with lymph node metastases than in bone metastases.

Prognostic value of metabolic tumor volume and total lesion glycolysis assessed by 18F-FDG PET/CT in endometrial cancer.

OBJECTIVE: Surgical staging is the most confidential method for prognosis prediction. However, in which stage the surgery is needed and the treatment management of these patients is controversial. Presentation of new determinant factors with imaging methods for prediction of poor prognosis can provide better disease management. The aim of our study was to demonstrate the ability of metabolic tumor volume and total lesion glycolysis as a prognostic factor to predict the disease-free survival time, necessity of adjuvant radiotherapy-chemotherapy, and the association of these parameters with the clinicopathological features. METHODS: Forty-four endometrial cancer diagnosed patients whose PET/CT scans were performed for treatment planning were included in our study. Metabolic parameters (SUVmax, metabolic tumor volume, total lesion glycolysis) of the primary tumor were calculated. Abdominal hysterectomy was performed for all patients. Histopathologic findings were noted. Patients were followed for 31.4 ± 14.8 months. RESULTS: Metabolic tumor volume and total lesion glycolysis were significant prognostic factors for disease-free survival, whereas SUVmax did not effect disease-free survival. According to regression analysis, only metabolic tumor volume was found significant for radiotherapy planning (cutoff metabolic tumor volume; 26.30 ml). There was significant association between metabolic tumor volume, total lesion glycolysis and early-stage, myometrial invasion, and lymph node positivity. We observed only weak association between SUVmax and myometrial invasion. ROC curve calculated metabolic tumor volume and total lesion glycolysis cutoff values as 19.6 ml and 90 g for early-stage, 14.3 ml and 173.4 g for myometrial invasion, and 29.7 ml and 283.1 g for lymph node positivity, respectively. CONCLUSION: Metabolic tumor volume and total lesion glycolysis may be used as prognostic factors for endometrial cancer. The association between SUVmax and clinical findings, disease-free survival, histopathological features are weak. Further studies are needed for demonstrating the prognostic value of metabolic volumetric parameters.