BLADDER WALL RADIATION-DOSE IN HUMANS FROM FLUORINE-18-FDOPA

PET, in conjunction with F-18-fluorodopa (FDOPA), has become the stand ard technique to assess basal ganglia degeneration in patients with mo vement disorders. Based on published dosimetry data, the injected dose of FDOPA is limited to ill Mbq (3 mCi) because of exposure to the bla dder wall, which is the critical organ for such studies, These dosimet ry studies are based on mathematical models for the bladder radioactiv ity accumulation and clearance when the subjects were asked to void ap proximately 2 hr after the intravenous injection of FDOPA. In this stu dy, we improved the radiation dose estimate to the bladder wall using dynamic PET to image the bladder during the uptake phase as well as be fore and after voiding, Methods: The subjects were tested on a new pro tocol, They were hydrated preinjection and given a first bladder void break at 40 min postinjection and a second void at the end of study at 120 min, Results: The MIRD model, applied to the data collected from 10 adults of both sexes, yielded an average absorbed dose of 0.15 +/- 0.08 mGy/MBq (0.57 +/- 0.28 rad/mCi). Conclusion: This absorbed dose i s significantly lower than previous estimates and allows for FDOPA inj ections up to 333 Mbq (9 mCi).