Washout studies of ¹¹C in rabbit thigh muscle implanted by secondary beams of HIMAC.

Heavy ion therapy has two definite advantages: good dose localization and higher biological effect. Range calculation of the heavy ions is an important factor in treatment planning. X-ray CT numbers are used to estimate the heavy ion range by looking up values in a conversion table which relates empirically photon attenuation in tissues to particle stopping power; this is one source of uncertainty in the treatment planning. Use of positron emitting radioactive beams along with a positron emission tomograph or a positron camera gives range information and may be used as a means of checking in heavy ion treatment planning. However, the metabolism of the implanted positron emitters in a living object is unpredictable because the chemical forms of these emitters are unknown and the metabolism is dependent on the organ species and may be influenced by many factors such as blood flow rate and fluid components present. In this paper, the washout rate of ¹¹C activity implanted by injecting energetic ¹¹C beams into thigh muscle of a rear leg of a rabbit is presented. The washout was found to consist of two components, the shorter one was about 4.2+-1.1 min and the longer one ranged from 91 to 124 min. About one third of the implanted positron activity can be used for imaging and the rest was washed out of the target area.