TLD estimation of absorbed dose for 131I on the surface of biological organs of REMCAL phantom

In nuclear medicine, the accuracy of absorbed dose of an internally distributed radiopharmaceuticals estimated by the MIRD (medical internal radiation dose) method depends on the cumulated activity of the source organs and their mass. The usual method for obtaining the cumulated activities are: 1) direct measurements by a) positron emission tomography (PET) and b) single photon emission computed tomography (SPECT) 2) extrapolation from animal data and 3) calculations based on the mathematical biokinetic model. Among these methods, extrapolation of animal data to humans includes inevitable inaccuracy due to large interspecies metabolic differences with regard to the administered radiochemical. Biokinetic modeling requires adequate knowledge of various kinetic parameters, which is based on some biological assumptions. Direct measurements can provide cumulated distributions with fewer biological assumptions. But direct measurements of PET/SPECT are difficult to perform routinely. A method has been developed to obtain the surface dose of different biological organs by using TLDs. Here, a number of TLDs are placed just above the surface of the biological organs of the REMCAL Alderson human phantom filled with water. Firstly, investigation of the accuracy of this method by calibration studies using the said phantom, which is having the entire biological organ intact and simulate the organs as human body is done. These organs are filled with the known activity of the radioisotope. In the present study, estimation of radiation dose received by fifteen different target organs, when the known activity was filled in the three major organs of interest was carried out