Purpose: The utility of positron emitter nuclei generated by photonuclear reactions was verified for X-ray beam monitoring in a phantom.
Materials and methods: Positron emission tomography-computed tomography (PET-CT) images of a gelatinous water phantom (H(2)O target) and a polyethylene phantom (CH(2) target) were acquired 5 min after delivering a dose of 17 Gy with an X-ray beam energy of 21 MV. Reconstructed PET images and the calculated half-life showed that the positron emitters of (15)O (half-life 122.2 s) in the H(2)O target and (11)C (half-life 20.4 min) in the CH(2) target were generated by photonuclear reactions.
Results: A comparison was made between measured activity and dose distributions for each target. The measured times of annihilation gamma rays from the positron emitter nucleus were 10 and 30 min for the (15)O nucleus in the H(2)O target and the (11)C nucleus in the CH(2) target, respectively. The activity distributions of the (15)O and (11)C positron emitter nuclei were similar to the measured dose distributions for both depth and lateral directions except for dose buildup and collimator edge regions. It was confirmed that no activity was detected at an X-ray energy of 14 MV, which was far below the energy threshold for both photonuclear reactions.
Conclusion: It was estimated that the PET-CT image acquired from the activity of the (15)O and (11)C positron emitter nuclei might provide the area of X-ray beam irradiation in a phantom.