There has been one change in the computer program producing these S tables which should be mentioned.

A geometric model that takes into account the changes in size, shape and position of the uterus during pregnancy has been designed for calculating the radiation dose to the uterus and the fetus from a radionuclide in the mother's bladder. The bladder is assumed to fill at a constant rate to 300 ml before voiding. The average dose in rads per photon emitted from a source in the bladder during one bladder filling has been calculated for monoenergetic photons of 0.02, 0.03, 0.05, 0.1, 0.2, 0.5, 1 .O, 1.5, 2.0 and 4.0 MeV. Since the dose to specific organs of the fetus could not be calculated, the fetal space was divided into 12 compartments. The dose was calculated for each compartment, for the average of the entire fetal space, and for the uterus. The average dose per photon to each compartment decreases as the fetus increases in size. The highest dose rate to the uterine wall occurs at the point where it touches the bladder. Because the uterus enlarges, the point on the uterus receiving the highest dose rate changes during pregnancy.

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The c o e f f i c i e n t of v a r i a t i o n f o r these values i s greater than 50%.

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