Development of a signal processing system to control a tumor positioning system based on annihilation gamma-rays measured using several pairs of scintillation detectors

The authors have been studying a new tumor tracking system for stereotactic radio surgery, composed of several pairs of scintillation detectors that detect annihilation gamma rays from radioactive medicine, such as ¹⁸F-FDG, in tumor tissue. For that purpose, a signal processing system was developed based on an ASIC (MPX-08, Nova), which can output the logical pulses when the signals from the photomultiplier tubes (PMTs) are above the preset discrimination level. Results obtained experimentally using a ²²Na point source show that the system can control erroneous irradiation outside the expected region to less than 1.8%, even when the source moved with speed of 15 mm/s. Moreover, the computer simulation showed that the system can work with erroneous irradiation of less than several percent, even for volumetric sources, considering the three-dimensional distribution of ¹⁸F-FDG near a lung tumor. (author)