Radiation Dose to Bladder Wall from Technetium-99m Accumulated in the Bladder Contents

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The standard MIRD model for the calculation of the radiation dose to the urinary bladder wall, per unit of activity accumulated in the bladder contents, has inherent limitations mainly associated with the assumption of a constant bladder volume. In this work accurate corresponding calculations are presented of bladder dose from 99 Tc m accumulations, performed through a home-developed Monte Carlo simulation code and using the dynamic geometry model proposed in MIRD Pamphlet No 14 for the simulation of the bladder. Radiation dose per unit of 99 Tc m activity accumulated in the bladder was calculated, for various bladder filling volumes, both at the bladder inner surface and as a function of depth within the bladder wall. The effect of backscatter from the bladder surrounding tissue was investigated and was found to influence photon dose calculations by as much as 25%. Results were used to derive parameterisation functions giving bladder wall surface and depth dose, with respect to bladder filling volume. These functions can be used, in combination with any dynamic physiological model, for accurate bladder wall depth dose estimations per unit of 99 Tc m administered activity.