Characterization of a fast timing and energy spectroscopy system for real-time range verification in particle therapy

A compact high-throughput gamma-ray timing and energy spectrometry systems has been characterized with respect to time and energy resolution at detector loads up to 1.5 Mcps by using 0.1-12.5 MeV bremsstrahlung and a common radioactive source. The detection system, developed for range assessment in particle therapy based on the Prompt Gamma-Ray Timing (PGT) technique, consist of a commercial ⌀2”×1” or ⌀2”×2” CeBr 3 scintillation detector with photomultiplier readout (Scionix), coupled to a digital plug-on spectrometer (U100) by Target Systemelektronik. The excellent time structure of the bremsstrahlung beam at ELBE (HZDR) allowed measuring the system time resolution simultaneously for 0.1-12 MeV photons. Also, the beam current and thus the detector load could be varied in a wide range. The energy resolution was determined in parallel with a 60 Co-source attached to the detector. Source and bremsstrahlung photons were separated by means of cuts in the timing spectra measured against the accelerator RF. The detection system could demonstrate a time resolution of < 260 ps (FWHM) for energies above 3 MeV with the smaller crystal, and an energy resolution of < 3.7% at 1.173 MeV for both crystals, up to detector loads of 1.4 Mcps and a corresponding system throughput of ~ 600 kcps. This fits well with the design goals of the detection system. Corresponding units shall be used for measuring PGT spectra during patients treatments with proton beams, in order to verify the proton beam range for single beam spots in Pencil Beam Scanning (PBS) mode. Range verification is considered a key for reducing margins and for improving precision and health outcome of particle therapy.