Radionuclide photon dose kernels for internal emitter dosimetry

Photon point dose kernels and absorbed fractions were generated in water for the full photon emission spectrum of each radionuclide of interest in nuclear medicine, by simulating the transport of particles using Monte Carlo. The kernels were then fitted to a mathematical expression. Absorbed fractions for point sources were obtained by integrating the kernels over spheres. Photon dose kernels and absorbed fractions were generated for the following radionuclides: I-123, I-124, I-125, I-131, In-111, Cu-64, Cu-67, Ga-67, Ga-68, Re-186, Re-188, Sm-153, Sn-117m, Tc-99m. The Monte Carlo simulation was verified by comparing the dose kernels to published monoenergetic photon kernels. Further validation was obtained by generating an I-125 brachytherapy seed kernel and comparing it with published data. Since Monte Carlo simulation was initialized by sampling from the complete photon spectra of these radionuclides, interpolation between monoenergetic kernels and absorbed fractions was not required. The absorbed-fraction due to uniform spherical distributions can be directly applied for use in internal dosimetry. In addition, the kernels can be used as input for three-dimensional internal dosimetry calculations.