18F FDG PET/CT blood flow imaging in urinary bladder cancer : Nuclear medicine’s answer to the oncologists’ question of muscle invasion

Introduction: Background :

Muscle invasion in urothelial carcinomas is a treatment defining parameter. Magnetic resonance imaging (MRI) is the gold standard modality to know about muscle invasion. Positron emission tomography imaging with 18Fluorine-fluorodeoxyglucose (FDG PETCT) has demonstrated utility in metastasis evaluation of carcinoma urinary bladder, but its utility in tumour (T) staging is limited owing to high urinary FDG concentration. We tried early dynamic imaging and the findings helped in better ‘T’ staging of carcinoma urinary bladder.

Aim / purpose:

The aim of this study was to identify muscle invasion in bladder cancer using a novel scanning protocol that takes advantage of the angiogenesis observed in malignancies and the kidneys’ physiology of delayed excretion of 18F-FDG into the urinary bladder.

Methods: Early dynamic PET/CT and 18F-FDG scans were performed on 14 patients with pathology confirmed bladder cancer. A series of 5 frames of 2 minutes each, starting at injection time, were obtained on each patient’s urinary bladder. SUV max was calculated for each frame as (SUVmax_1, SUV max_2, SUV max_3, SUV max_4, SUV max₅). Delayed images were acquired after 45 minutes for metastasis evaluation.

Results: Muscle invasion in pathology report was considered as the gold standard. Patients with muscle invasion demonstrated increased SUV max in the first two frames. Patients without muscle invasion demonstrated no increase in SUV max in initial two frames. Patients with muscle invasion also showed consistent increase in the SUV max over the next consecutive frames. Patients without muscle invasion demonstrated no significant increase in SUV max over the next consecutive frame. The average maximum standard uptake values (SUVmax SD), at 2 to 4 minutes postinjection, of bladder wall areas in muscle invasion positive and muscle invasion negative patients were 8.5 and 1.8 respectively

Conclusions: Out of 10 patients who showed muscle invasion in pathology, 8 patients demonstrated increased SUV max in the initial two frames , 1 patient showed no uptake owing to complete resection in TURBT, 1 patient showed no uptake (pathology turned out to be neuro endocrine origin) . So, Our study findings early dynamic 18F FDG PET CT imaging can be used as an adjunct to find the muscle invasion status in carcinoma bladder patients.