Dose estimation from in-beam PET imaging of 11C and 15O beams

Monitoring the stopping position of primary ions in a tumor is desirable for effective tumor treatment by ensuring tumor coverage and preventing overdose exposure to normal tissues in ion therapy. The use of positron-emitting ion beams, such as
¹¹
C and
¹⁵
O, has been suggested for range verification in ion therapy exploiting in-beam positron emission tomography (PET) imaging, where the ion stopping position is visualized with a high signal-to-noise ratio. We have previously demonstrated the feasibility of in-beam PET imaging for range verification of
¹¹
C and
¹⁵
O ion beams. In this study, we investigate a method for prediction of dose profiles from PET images for both
¹¹
C and
¹⁵
O ion beams for the first time. The depth dose was measured in water for both ion beams with momentum acceptance (MA) of 0.5% and 5%. The PET images were obtained for an irradiated polymethyl methacrylate (PMMA) phantom with both beams under the same MA conditions. The beams with smaller MA were considered as mono-energetic beams and were used to obtain the best energy weights for reproducing the measured PET activity of the beams with MA of 5%. Then the obtained optimum energy weights were used for prediction of dose profiles for the beams with MA of 5%. The predicted dose profiles were in overall good agreement with the measured ones and the distal fall-off positions at 80% of the Bragg peaks were also predicted within 0.2 mm for both
¹¹
C and
¹⁵
O ion beams.