Washout measurement of radioisotope implanted by radioactive beams in the rabbit

Abstract

Washout of 10C and 11C implanted by radioactive beams in brain and thigh muscle of rabbits was studied. The biological washout effect in a living body is important in the range verification system or three-dimensional volume imaging in heavy ion therapy. Positron emitter beams were implanted in the rabbit and the annihilation gamma-rays were measured by an in situ positron camera which consisted of a pair of scintillation cameras set on either side of the target. The ROI (region of interest) was set as a two-dimensional position distribution and the time-activity curve of the ROI was measured. Experiments were done under two conditions: live and dead. By comparing the two sets of measurement data, it was deduced that there are at least three components in the washout process. Time-activity curves of both brain and thigh muscle were clearly explained by the three-component model analysis. The three components ratios (and washout half-lives) were 35% (2.0 s), 30% (140 s) and 35% (10 191 s) for brain and 30% (10 s), 19% (195 s) and 52% (3175 s) for thigh muscle. The washout effect must be taken into account for the verification of treatment plans by means of positron camera measurements.

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

“…Positron emitter distributions were calculated by internally combining proton fluence with experimental cross sections (12). Besides the main (p, pn) channels on 12 C and 16 O yielding 11 C and 15 O (12), respectively, further proton interactions with N, O, Ca, and P, resulting in 11 C, 13 N, 38 K, and 30 P production, respectively, were included. Shorter-lived emitters were neglected because of the low-production cross-section and the offline PET imaging approach.…”

“…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.…”

“…For the low-perfusion fat and compact bone, M s and T 1/2,bios were set to 0.9 and 15,000 s, respectively. In soft bone, intermediate values of M s and T 1/2,bios were approximated to 0.6 and 8,000 s. For all remaining tissue, an average value of M s = 0.55 and T 1/2,bios = 3,500 s was used in spine sites, while a value of M s = 0.35 and T 1/2,bios = 10,000 s was used for head sites, based on the results of animal studies in muscle and brain, respectively (16). In the patient with ocular melanoma, reduced perfusion (M s = 0.8, T 1/2,bios = 10,000 s) was assumed within the eye, whereas an average value of 0.45 (M s ) and 6,000 s (T 1/2,bios ) was used for the surrounding tissue.…”

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.…”

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/…”