Development of improved methods for internal dosimetry calculations

Abstract

This dissertation presents improvements in three areas of nuclear medicine dosimetry: diagnostic, therapy, and bone dosimetry. For diagnostic nuclear medicine dosimetry, a series of five pediatric head and brain dosimetric models are developed based on the new adult model of the Medical Internal Radiation Dose Committee (MIRD). The EGS4 Monte Carlo code is used to tabulate absorbed fractions of energy (AFs) for photon and electron sources. Subsequently, radionuclide S values are tabulated for use in pediatric neuroimaging studies. In therapy nuclear medicine dosimetry, a new tool for nonuniform activity distributions is developed based on the MIRD methodology of dose calculation. Three‐dimensional cumulated activity derived from single photon emission computed tomography (SPECT) images can be convoluted with S values calculated for the same voxel arrangement to generate average dose to voxels within the SPECT images. Voxel S values are calculated using the EGS4 code for 21 voxel sizes up to 1.0 cm. A specific absorbed fraction interpolation schema is then derived for other voxel sizes. Examples of the clinical use of this dose calculation method are provided. Finally, in bone dosimetry, three‐dimensional transport models of electrons are developed for trabecular and cortical bone. These models are used with the EGS4‐PRESTA code to calculate AFs. A one‐dimensional transport model is also developed to evaluate improvements using three‐dimensional transport. AFs are then used to calculate bone site‐specific and skeletal‐averaged S values. Differences seen with previously published bone S values are analyzed. These skeletal‐averaged S values are then used to estimate dosimetric advantage of beta‐emitting radionuclides for the palliation of bone pain from bone metastases.