Usefulness of positron-emission tomographic images after proton therapy

Purpose: To examine the positron emission tomography (PET) image obtained after proton irradiation and investigate the usefulness of the image for confirmation of the irradiated volume in proton radiotherapy (RT). Methods and Materials: A homogenous phantom was irradiated separately by carbon-ion and proton beams and the images obtained were compared. The PET images of cancer patients just after proton RT were then taken after informed consent. Results: In the PET image produced by carbon-ion beams, the high pixel counts in the image corresponded to the Bragg peak; however, in that produced by proton beams, they were visible throughout the entire track of the proton beams and were not related to the Bragg peak. The PET image of patients treated with proton RT was similar to that of the phantom experiment. Conclusion: The PET image after proton RT was different from that of carbon-ion RT. It was found that the PET image was very useful in proton RT to verify treatment planning. (C) 2002 Elsevier Science Inc.