Significance and direction of advancement in calibration phantom for external counting system

This review concerning the calibration phantom for external counting system described its present states and problems, significance of its advancement, attempt to grade up it and tasks in future. The phantom, filled with radioactive materials, is used for determining the calibration constants (counting efficiency) for calculating the internal exposure dose of the human body containing radioisotopes which can be measurable with external counting systems like the whole body counter, thyroid-monitor and lung-monitor. At present, parameters for estimating the dose like retention function are not for those for the person in problem but those for ordinary population. Advancement would be done by making the phantom more precise, by evaluating the influence of the precision on the dose estimation and by providing a guideline to make the practically useful phantoms. A voxel phantom was made up as an instance of the attempt to improve the phantom, which was validated by actual measurement of the body parts. The task was considered to be the improvement of the phantom together with seeking for the direction of the improvement. (K.H.)