Application of heavy ion CT

The precision in heavy ion radiotherapy treatment planning depends on the accuracy of conversion from CT value to relative stopping power to water. This accuracy is directly related to the accuracy of the calculation of the charged particle range in a patient's body. In treatment planning at National Institute of Radiological Sciences (NIRS), the conversion table from CT numbers into relative stopping powers to water has been created on base of the polybinary tissue model. However, it has not been fully verified that the model is accurate enough for real animal tissues. In order to improve heavy ion radiotherapy more precisely, we have to evaluate the accuracy of the polybinary tissue calibration in animal tissues. We have measured animal tissue samples such as the adipose tissue, muscle and bone with a heavy-ion CT (HICT) and an x-ray CT. The x-ray CT image was converted to the image of relative stopping power by using the table derived from the polybinary tissue calibration. With the HICT, the two dimensional distribution of relative stopping power is obtained directly. The comparison of two CT images enable us to verify the accuracy of the conversion table derived from the polybinary tissue calibration. (author)