Improving calibration for in-vivo radioactivity monitoring
Unlike external radiation monitoring internal radiation exposure measurements are more complicated, time consuming and potentially less accurate. To answer this need the IDEA project focused on improving internal dosimetry techniques including bioassay and in-vivo studies for assessing their applicability in routine practice. One of the key project results involves a comparative study of calibration methods using phantom measurements and computerised techniques involving specific Monte Carlo simulation code. Thereby, measurements of bottle phantoms filled with a solution of holmium-166m and cobalt-60 on a whole body counter in scan geometry were compared against results coming from the computer simulations. In order to assess the more accurate method, uncertainty factors of both calibration methods were calculated. A finite amount of events give rise to statistical uncertainty factors for both the measurement and the simulation. Other uncertainty sources include calibration sources of the bottle phantoms, geometrical reasons, averaging techniques and models for simulated physical effects. All uncertainties were stated as one standard deviation. It was shown that the calibration by simulation displays a better accuracy (3.8%) than the calibration by measurement (4.1%). Therefore, the simulation technique has the potential to be exploited in the calibration studies of a whole body counter and anthropomorphic phantoms. Using Medical Internal Radiation Dose (MIRD) phantoms, uncertainty factors for different weight and height of the subject as well as inhomogeneous distributions in the human body were also calculated. The interesting findings are expected to improve the efficiency of the calibration technique and in-vivo monitoring methods.
