Evelyn E. Watson

Mathematical models and specific absorbed fractions of photon energy in the nonpregnant adult female and at the end of each trimester of pregnancy

Mathematical phantoms representing the adult female at three, six, and nine months of gestation are described. They are modifications of the 15-year-old male/adult female phantom (15-AF phantom) of Cristy and Eckerman (1987). The model of uterine contents includes the fetus, fetal skeleton, and placenta. The model is suitable for dose calculations for the fetus as a whole; individual organs within the fetus (other than the skeleton) are not modeled. A new model for the nonpregnant adult female is also described, comprising (1) the 15-AF phantom; (2) an adjustment to specific absorbed fractions for organ self-dose from photons to better match Reference Woman masses; and (3) computation of specific absorbed fractions with Reference Woman masses from ICRP Publication 23 for both penetrating and nonpenetrating radiations. Specific absorbed fractions for photons emitted from various source regions are tabulated for the new non;pregnant adult female model and the three pregnancy models.

Radiation absorbed dose to the embryo/fetus from radiopharmaceuticals.

Radiation protection practice requires the knowledge of estimated absorbed radiation doses to aid in the understanding of the potential detriment of various exposures. In nuclear medicine, the radiation doses to the internal organs of the subject are commonly calculated using the MIRD methods and equations. The absorbed dose to the embryo or fetus has long been an area of concern. The recent release of the pregnant female phantom series, and its incorporation into the MIRDOSE 3 computer software, has made possible the estimation of absorbed doses from radionuclides in the body to the fetus in early pregnancy and at 3, 6, and 9 mo gestation. A survey of several major medical institutions was made to determine the radiopharmaceuticals which might be given, whether intentionally or not, to women of childbearing years. Biokinetic data for these radiopharmaceuticals were gathered from various documents and other resources, and the absorbed doses to the embryo and fetus at these different stages of gestation from radiations originating within the mothers organs were estimated. In addition, information about activity distributed within the placenta and fetus was included where quantitative data were available. These absorbed dose estimates can be used to evaluate the risk associated with the use of different radiopharmaceuticals so that a more informed evaluation of the risks and benefits of the different procedures may be made. Further research is needed into the mechanisms and quantitative aspects of the placental transfer of many radiopharmaceuticals.

Dose to the fetus from radionuclides in the bladder.

Abstract A geometric model that takes into account the changes in size, shape arid 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 mothers 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, 1.0, 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.

Calculating dose from remaining body activity: a comparison of two methods.

Two methods for calculating the radiation dose from remaining body activity have been suggested. One requires correction of the cumulated activities so that they reflect the activity uniformly distributed in the total body. The other method requires correction of the S values so that a value of S for the target organ from the remainder of the body is obtained. These two methods give the same answer. We have examined these methods and the number of steps required to calculate the radiation dose in each case. Our results show that the method of correcting the cumulated activities is preferred, especially if the number of source and target organs is large and a computer equipped with the necessary software is not available.

A history of medical internal dosimetry.

This paper presents a short history of the development of medical internal dosimetry. It reviews the evolution of the equations and discusses the development of various mathematical models used to improve radiation absorbed dose estimates. The contributions of Leonidas Marinelli, Edith Quimby, William Mayneord, Robert Loevinger, Walter Snyder, and others are emphasized.

Effect of stable scandium on the long-term whole body retention of intravenously administered 46Sc citrate in the rat.

The effect of stable scandium on the whole-body retention and tissue distribution of

Radiation dose to the lungs from ventilation studies with 133Xe.

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Dosimetry of leukocytes labeled with 99Tcm-albumin colloid.

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Interfacing a multichannel analyzer to a minicomputer

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MIRD Pamphlet No. 17: The Dosimetry of Nonuniform Activity Distributions—Radionuclide S Values at the Voxel Level

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