Jämförelse av aktivitet i urinblåsan hos 18F-PSMA-PET patienter med och utan hydrering

Sammanfattning: Background: Prostate cancer is the most prevalent form of cancer affecting men.In case of biochemical recurrence, positron emission tomography (PET) targeting prostate-specific membrane antigen (PSMA) on prostate tumor cells is primarily used, in combination with computed tomography (CT), for detection and localization of recurrence. Research for optimizing a PSMA-ligand with high affinity for tumor cells and minimal excretion to the urinary bladder is constantly ongoing, in order to allow better evaluation of the prostate and nearby regions. One such ligand is 18F-PSMA-1007, which was expected to be excreted in the urinary bladder at a rate of 5-10%. However, after switching from diagnostic to low-dose CT, the elimination of 18F-PSMA-1007 in the bladder was higher than expected. Purpose: To evaluate whether hydration during the accumulation period could affect the activity concentration in the bladder. Materials and Methods: The study involved analyzing PET-CT scans obtained from two prostate cancer patient groups who underwent 18F-PSMA-1007-PET with low-dose CT. The groups consisted of 20 participants each, with one group hydrating during the tracer’s accumulation time, while scans from the comparison group were obtained from a time point where patients did not receive instructions about water intake. The amount of radioactivity was measured by placing a standardized 3.00 cm Volume of Interest (VOI) on the bladder, which was then adjusted based on the individual size and shape of the patients' bladder. From the VOI, a standardized uptake value (SUV) was determined, which can be represented as either SUVmean or SUVmax. These values represent the average tracer concentration within a VOI and the highest concentration of the tracer in the urinary bladder, respectively. Results: SUV in the urinary bladder was lower for the hydrated group, where the SUVmean was 1,55 vs 4,5 (p=0,011) for the non-hydrated group. Similar values were obtained for SUVmax, 2,3 vs 6,65 (p< 0,003). Conclusion: This retrospective study suggests that water intake during the accumulation period leads to significantly lower activity concentration in the bladder among these patients, which benefits the detection of recurrences in adjacent areas.