Washout effect in rabbit brain: in-beam PET measurements using 10C, 11C and 15O ion beams

In particle therapy, in-beampositron emission tomography (PET) is expected to enable in situ noninvasive confirmation of the treatment delivery. For accurate range and dose verification or threedimensional (3D) volume imaging, however, correction of the biological washout effect in a living body is necessary. In this study, wemeasured thewashout rate in a rabbit brain using the recently developed technology for oxygen beam radiation aswell as carbon ion beam radiation. Tomeasure components of washout, three radionuclides, C, C and O,whichwere generated as secondary beams in theHeavy IonMedical Accelerator inChiba (HIMAC), were irradiated on the rabbit brain under two conditions, live and dead. In-beamdatawere acquired by ourwhole body dual-ring OpenPET,which enables 3D in-beam imaging. Regions of interests (ROIs)were set as a 3Dpositron distribution and the time activity curves (TACs) of the irradiated fieldwere acquired.We obtained the washout rate for those conditions based onmultiple componentmodel analysis. A difference between washout speed in C ions and the O ionswas observed. The observedmedium and slow biological decay rates of C ions in rabbit brainwere 0.30min and 0.004min, respectively. Those values were consistent with the previous rabbit study results acquired by other imagingmodalities, such as the pair of positron cameras or our single-ring small animalOpenPETprototype. The observed medium and slowbiological decay rates of O ionswere 0.72min and 0.024min, respectively, whichwere faster than those of the C ion. Also, themediumbiological decay rate of O ionswas close to thewashout rate in cerebral blood flow (CBF)measurements by dynamic PETwith O-labeledwater. These results should help to establish an accurate washout correctionmodel.