Improvement of purity of produced 15O beams for OpenPET

In ion therapy, it is ideal to use radioactive ion beams for in-beam positron emission tomography (PET) imaging in order to visualize the irradiation field for treatment. In cancer treatment with light ions,
¹⁵
O beam is a good candidate for tumor treating and monitoring the delivery of the dose by (PET) imaging. Moreover, a combination of different positron emitter ions, such as
¹¹
C and
¹⁵
O, might be favorable for a selected clinical situation in the near future for radiation therapy. We have recently produced
¹⁵
O beams in the Heavy Ion Medical Accelerator in Chiba (HIMAC) using an optimized target of polyethylene. But the purity of the produced beams was around 75%, which is not satisfactory for clinical utilization. Therefore in this study we focused on improvement of the purity of the produced beam by adding a wedge-shaped degrader within the beam line. We inserted an aluminum degrader with the thickness of 1.76 cm into the secondary beam line. The purity of the produced beam for the polyethylene target with thicknesses of 5 cm and 11 cm were measured. The in-beam PET images of the produced beams with and without the aluminum degrader in the beam line were obtained using our whole-body dual-ring OpenPET system. The purity of the beam produced by inserting the degrader into the beam line was increased from 75% to 97%.