Optical imaging for the characterization of radioactive carbon and oxygen ion beams

Heavy ion therapy is a promising cancer therapy technique due to the sharper Bragg peak and smaller lateral scattering characteristics of heavy ion beams as compared to a proton therapy. Recently, the potential for radioactive ion beam therapy has been investigated in combination with the OpenPET system to improve the accuracy of in vivo beam range verification. However, the characteristics of the radioactive ion beams have not been investigated thoroughly. Optical imaging has been proposed as a novel high-resolution beam range estimation method for heavy ion beams. In this study, high-resolution luminescence imaging and Cerenkov light imaging were performed for the range estimation of radioactive ion beams such as ¹¹C and ¹⁵O in the Heavy Ion Medical Accelerator in Chiba (HIMAC) secondary beam line. A polymethyl methacrylate (PMMA) phantom (10.0  ×  10.0  ×  9.9 cm³) was irradiated by ¹¹C and ¹⁵O ion beams. In order to obtain the in-beam luminescence and off-line beam Cerenkov light images, an optical system was used that consisted of a lens and a cooled CCD camera. The Bragg peaks and stopping positions of the ¹¹C and ¹⁵O ion beams could be visualized by using the luminescence and Cerenkov light imaging, respectively. The Bragg peaks showed a good correlation with the peak of the luminescence profile with a positional discrepancy of 1 mm and 0.4 mm for the ¹¹C and ¹⁵O ion beams, respectively. In conclusion, optical imaging using luminescence and Cerenkov light could be used for the precise range estimation of radioactive ion beams.