Feasibility of secondary 15O beam production for in-beam PET

For the purpose of in situ visualization of an irradiation field in particle therapy, it is ideal to use radioactive beams for in-beam positron emission tomography (PET) imaging. In the Heavy Ion Medical Accelerator in Chiba (HIMAC), there is a beam course to produce ¹¹C and ¹⁰C as secondary beams, but generation of ¹⁵O has never been investigated. This study was devoted to analysis of the feasibility of secondary ¹⁵O production for in-beam PET by ¹⁶O primary beam in different absorbing materials (targets) with various thicknesses in order to find out the optimum target material and its thickness. The study was performed using analytical method, LISE++ code, and the Monte Carlo method, PHITS code. The calculation results showed that the highest intensity of the secondary ¹⁵O beam observed for primary ¹⁶O beam decelerating in liquid hydrogen but practically almost impossible to apply. The final optimum target was considered to be polyethylene with thickness of 11 cm. The ¹⁵O beam was produced in the HIMAC secondary beam line using the optimum target and the in-beam PET imaging was presented for a PMMA phantom irradiated with the produced beam.