Dynamic absorbed dose calculations to the urinary bladder wall for the ICRP compartmental models of iodide and technetium

• Aim/Introduction: The urinary bladder wall is a radiosensitive organ that can receive a high absorbed dose from radiopharmaceuticals used even in diagnostic nuclear medicine. The commonly used method to calculate the absorbed dose to the urinary bladder wall is to apply absorbed fractions or S-values derived for a static volume of the content e.g. 200 mL for adult males. However, there are some dynamic models to estimate the photon and electron absorbed dose contributions to the inner surface or the mean absorbed dose to the bladder wall. These models have only been applied on adults and use descriptive biokinetic models for the transfer of radionuclides. The aim of this work is to estimate the absorbed dose, based on Monte Carlo-simulated dynamic urinary bladders and the ICRP compartmental biokinetic models of iodide and pertechnetate. The calculations include sex specific absorbeddose and estimations for preadults of 15- 10- 5- 1-year and newborn.Materials and Methods: S-values were calculated for different volumes of the content with a fix mass of the wall. As an approximation a spherical shape was assumed. Calculations were based on anatomical and physiological data of the reference sets of values given in ICRP Publication 89. The reference values were given for both male and female subjects of six different ages: newborn, 1-, 5-, 10-, 15-years, and adult. The elemental compositions of the urinary bladder wall and content were taken from the ICRP Publication 110.Results: For adult male assuming a urinary flow rate of 1600 ml/day, an initial urine volume of 100 ml, a voiding volume at 300 ml and a residual volume of 30 ml, the cumulated activity will for intravenously administered activity of Tc-99m pertechnetate be 30 % lower than assuming a 3.5 hour voiding interwall. The absorbed dose to the urinary bladder wall will be 64% lower also applying the dynamic S-values on the dynamic case. Using the same biological parameters for intravenous intake of I-131 iodide, the cumulated activity will be 60 % higher for the dynamic case and the mean absorbed dose to the urinary bladder wall 30 % lower.Conclusion: This project aims to perform more realistic calculation of absorbed dose to the urinary bladder calculations. This is done by tracking the activity in the urinary content at each time on compartment models and applying the time dependent activity to urinary flow and Monte Carlo simulated S-values.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Radiologi och bildbehandling (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Radiology, Nuclear Medicine and Medical Imaging (hsv//eng)

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