Measurement and verification of positron emitter nuclei generated at each treatment site by target nuclear fragment reactions in proton therapy.

PURPOSE: The purpose of this study is to verify the characteristics of the positron emitter nuclei generated at each treatment site by proton irradiation. METHODS: Proton therapy using a beam on-line PET system mounted on a rotating gantry port (BOLPs-RGp), which the authors developed, is provided at the National Cancer Center Kashiwa, Japan. BOLPs-RGp is a monitoring system that can confirm the activity distribution of the proton irradiated volume by detection of a pair of annihilation gamma rays coincidentally from positron emitter nuclei generated by the target nuclear fragment reactions between irradiated proton nuclei and nuclei in the human body. Activity is measured from a start of proton irradiation to a period of 200 s after the end of the irradiation. The characteristics of the positron emitter nuclei generated in a patient's body were verified by the measurement of the activity distribution at each treatment site using BOLPs-RGp. RESULTS: The decay curves for measured activity were able to be approximated using two or three half-life values regardless of the treatment site. The activity of half-life value of about 2 min was important for a confirmation of the proton irradiated volume. CONCLUSIONS: In each proton treatment site, verification of the characteristics of the generated positron emitter nuclei was performed by using BOLPs-RGp. For the monitoring of the proton irradiated volume, the detection of (15)O generated in a human body was important.