Comparison of measured and calculated internal absorbed doses in a heterogeneous phantom

The experimental validity of the MIRD (Medical Internal Radiation Dose Committee of the Society of Nuclear Medicine) internal-dose calculations was investigated. Internal radiation doses were measured in a phantom representing the MIRD mathematical phantom using a newly developed volumetric tissue-equivalent dose meter that could be moulded to reproduce the geometry of the phantom's mathematical organs. The MIRD Monte Carlo computer code ALGAM was adapted to simulate the experimental conditions and was run for each calculation with 60,000 photon histories. The experimental data and the theoretical calculations were compared for different combinations of six source organs and seven target organs using 60Co as the source of radiation. The results of this comparison indicated agreement between measured and calculated doses when the uncertainties associated with both techniques are considered. However, statistical analysis of the data also gave an indication that the Monte Carlo method might overestimate the internal absorbed doses since the agreement with the experimental data was found to be in one direction.