The effect of hydration on the dose to the urinary bladder wall during technetium-99m diethylene triamine...

A spherical bladder dynamic model for the estimates of the radiation dose to the bladder walls from intravenously injected radionuclides was implemented to investigate in theory the effect of hydration on the reduction of the bladder dose in technetium-99m diethylene triamine penta-acetic acid (99mTc) DTPA renography. This model gives due consideration to the variation with time of the urine flow rate to the bladder, following a known fluid load. According to the model, the estimated dose depends on the renal function, the fluid load, the time elapsed from the fluid load to the i.v. DTPA injection, the micturition volume and the residual urine volume. Experimental data concerning the values of these parameters for normal individuals were obtained from the literature. Calculations cover the time period from i.v. injection up to the time of the ninth postinjection void. Results show that the patient's condition of hydration is critical for the radiation protection of the bladder. It is shown that optimum combinations of the values of the parameters involved in the calculations exist, which minimize the radiation dose. On the basis of these results, a general protocol is proposed, referring to the hydration conditions under which the renal dynamic study may be normally carried out, with a minimal absorbed dose to the bladder walls (less than 0.045 mGy/MBq).