[Development of a moving target aiming system using an ultrasound imaging unit]

We developed an ultrasound imaging unit for gating the irradiation of proton beams or acquiring CT scan data for treatment planning according to the motion of tumors in the abdomen. In proton therapy, it is essential that the maximum region of dose rate distribution in a body always coincide with the volume of the tumor in motion during irradiation. Gated proton bean irradiation based on tumor motion could solve this problem and minimize undesirable dose distribution to normal tissues in the vicinity of the tumor. This device can generate the TTL level signal of time width corresponding to the period that the tumor would be sited in a region determined in advance, to control the various kinds of machines. Results of our preliminary experiment using X-ray irradiation showed that this aiming device was able to make the width of the gated irradiation area coincide with that of the planned area within a difference of about 0.5 mm.