Evaluation of the dose to the bladder wall using a dynamic balloon-bladder phantom and TLD measurements in 18F-FDG...

[18F]-2-deoxyglucose (18F-FDG) is one of the most useful radiopharmaceuticals in clinical positron emission tomographic imaging. Its final metabolic destination is the bladder, which accumulates the highest absorbed dose in the body during imaging. The aims of this study were to develop a dynamic bladder phantom to emulate the dynamic response of the bladder and to evaluate changes in the dose to the bladder wall during the imaging procedure. 18F-FDG of various concentrations can be drip-fed intravenously to the balloon-bladder at different uptake phases or extracted from the phantom during voiding. A dose evaluation model, introducing the concept of photon energy flux conversion into the dose calculation, is thus developed for clinical evaluation. The dose to the bladder wall using the proposed model is comparable to that measured using a thermoluminescence dosimeter (TLD), with a less than 5% discrepancy. The main advantages of the model are the use of the dose conversion factor, phi TLD, which is determined from real TLD measurements, and the ability to consider the dynamic characteristics of the bladder. To overcome the problems of diverse dose distributions among subjects, time-activity information provided by clinical bladder imaging is required, so that the method can be applied to other radiopharmaceuticals.