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 beta+ activity can be used for imaging and the rest was washed out of the target area.
To examine the reliability of quantitative positron emission tomography studies in the rat (Rat-PET), we assessed the influence of radioactivity accumulated in the Harderian glands on PET CMRglc determination. We measured CMRglc by PET and ex vivo dissection methods by using 2-[18F]fluoro-2-deoxy-D-glucose in rats with and without focal brain ischemia. The CMRglc values obtained by PET, after correcting with recovery coefficients, were higher than those measured by the ex vivo method at rostral slices, and reduction of the CMRglc in the ischemic brain was not demonstrated by PET in the frontal cortex. The radioactivity accumulated in the Harderian glands prevents the quantitative determination of CMRglc using Rat-PET.
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