Development of implantable real time micro dosimeter system

Although progress of radiation therapy in recent years is rapid, medical accidents like the irradiation of over and under dose occur frequently in Japan. To eradicate these accidents and to increase accuracy of radiation therapy, we are developing an implantable real time micro dosimeter system. CdTe semiconductor is used as an ideal detector. And the doses of radiation are monitored by measuring the magnetic field converted from the current. We investigated the relationship between dose rate and current value from CdTe semiconductor(4mmx4mmx0.5mm). The data showed that 70 to 90 nA of electric current is proportionally generated from the CdTe semiconductor when it is irradiated by a LINAC under an air condition by the dose rate of I similar to 6Gy/min. In addition, the proportion of irradiated dose and the current was confirmed under a subaqueous condition(15cm in depth). To investigate the influence of a magnetic, field on a human body, we calculated the tolerance frequency for human body using FEM simulation method. The data showed that the sending and receiving of data as a frequency of magnetic field should be set 100MHz or less. We are now miniaturizing the dosimeter circuit up to the size of inserted level by a fine needle.