Washout studies of¹¹C in rabbit thigh muscle implanted by secondary beams of HIMAC

Abstract

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.

Patient Study of In Vivo Verification of Beam Delivery and Range, Using Positron Emission Tomography and Computed Tomography Imaging After Proton Therapy

“…This prohibits the application of compartment models, which are well-established in conventional tracer imaging. Previous animal studies on the washout of 10 C and 11 C implanted ions or 11 C resulting from autoactivation of 12 C beams indicated the existence of a fast (biologic half-life [T 1/2 , biof ] ≈(2-10 s), medium (T 1/2 , biom ≈100-200 s), and slow (T 1/2,bios ≈ 3,000-10,000 s) component of biologic decay in rabbit thigh muscle and brain (15,16). In our offline imaging approach, the fast and medium processes have already decayed at the time of imaging.…”

“…Positron emitters such as 11 C and 15 O are produced via nuclear interactions along the protonbeam path, and can be imaged during (online) or shortly after (offline) treatment as a spatial marker of radiation-dose deposition. Previous offline and online phantom experiments indicated the sufficient accuracy of positron emission tomography (PET) imaging for the verification of proton range and field lateral position [(1,2) and citations therein].…”

Experimental verification of proton beam monitoring in a human body by use of activity image of positron-emitting nuclei generated by nuclear fragmentation reaction

“…Therefore, the biological washout effect in the metabolism of a living tissue is important for the verification of the absolute activity and the activity distribution of the positron-emitting nuclei induced by the proton irradiation. In studies in which the radioactive ion beam ( 11 C, 10 C) to a rabbit was irradiated, the decay curve has three components of a fast decay (decay constant *2-10 s), medium decay (decay constant *100-200 s), and slow decay (decay constant *3,000-10,000 s) [23,24]. The 50-65% of total activity is the fast and medium components.…”

“…The coefficient of the effect has been estimated to be the 50-65% of total activity [23,24]. However, the radioactive ion beam was irradiated to a living tissue in the study.…”

Proton therapy dosimetry using positron emission tomography

“…The simulation of using an on-line system showed losses in activity intensity from transportation to the offline system of up to 75%, depending on the type of tissue. Also, it was found that the effect of biological washout was lower than the previously estimated 50%-65%, although the overall effect was not quantified [37,38] . The study led by Parodi K took nine patients with different types of head and neck cancers and used a PET/…”