Calculation of the intake retention fraction and dose coefficients in Tc-99m-labelled compound for internal exposure for medical workers

Abstract

For recent decades, a considerable amount of Tc-99m has been stimulated for diagnosis radiopharmaceuticals because of its physical advantages. The increase in the use of Tc-99m makes naturally more chances of internal exposure for not only patients but also medical workers. The patient internal exposure by an intravenous injection has been assessed relatively well with the reports of International Commission on Radiological Protection (ICRP) or Medical Internal Radiation Dose(MIRD). However, there are few studies which can support its accurate assessment for medical worker who treats Tc-99m. In spite of the absence of information, the physiological information of each Tc-99m-labelled compound for patient, provided by ICRP, can be used optionally for worker exposure because the behaviors after uptake to blood are similar for patient and worker. Using the data, in this study, the data for bioassay were given as the intake whole-body retention and urinary excretion function. We selected the two most frequently used Tc-99m-labelled compounds based on statistical data; Tc-99m-phosphonate, pertechnetate. The data of the Human Alimentary Tract Model (HATM, publication 100) and the revised Human Respiratory Tract Model (revised HRTM, OW) were used for compartment models which depict the physiological behavior in body after intake. In case of Tc-99m-phosphonate, we adopted the systemic model for patient intake described in ICRP publication 53 based on the assumption that the behaviors after uptake to blood are similar for patient and worker. On the other hand, recent updated systemic model in OIR report could be directly adopted for pertechnetate. We used Birchall's algorithm for calculation and developed the module which could calculate the retention amounts in each compartment at given time by MATLAB. In addition, we fitted the functions as sum of exponential terms using ORIGIN and the fitting coefficients were provided. We also could calculate the committed dose coefficients for each compound using SAF values for photons provided by Cristy and Eckerman. The results in this study will be useful to estimate the intake and effective dose for medical field.