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A Unified Approach to Photon and Beta Particle Dosimetry

Department of Radiology, University of Nebraska Medical Center, Omaha, Nebraska

Correspondence: For correspondence or reprints contact: Peter K. Leichner, PhD, University of Nebraska Medical Center, Department of Radiology, Omaha, NE 68198-1045.

ABSTRACT

The purpose of this investigation was to develop a unified and practical method for photon and beta particle dosimetry. Methods: This was achieved by developing a point-source function that is equally valid for photons and beta particles. This function contains four fitting parameters. These were computed on the basis of Berger's tables for a wide range of photon and beta particle energies. Explicit formulas were derived for the absorbed fraction within and outside of spheres containing a uniform distribution of activity. For photons, calculations of the absorbed fraction at the center of spheres were compared with the results of Monte Carlo calculations. The two methods yielded essentially identical results, validating the approach used in this study. Results: The results of this study show that there are absorbed-dose gradients as a function of distance from the center of a sphere. These should be taken into account in absorbed-dose calculations. For beta particles, it is shown explicitly that for spheres with a radius of 0.08 cm, absorbed-dose rates from ¹³¹I and ⁹⁰Y beta particles are equal. Conclusion: An important feature of this work is that calculations can be made on the macroscopic, cellular and subcellular levels. The approach employed and results obtained in this work should be particularly useful for tumor dosimetry in radionuclide therapy and applicable radiobiological investigations.

Key Words: dosimetry • photon dosimetry • beta particle dosimetry