Room: Stars at Night Ballroom 1
Purpose: To replace a Multi-Layer-Ion-Chamber(MLIC) used to measure integral depth dose(IDD) profile in beam commissioning for Pencil Beam Scanning(PBS), we evaluated a novel system based on multilayer acrylic-disk radiation sensor(ADRS) designed to compensate for limitations such as electronic circuits, small diameter of ion-chamber and high-cost.
Methods: Multilayer-ADRS is made of multiple disks and consisted of disk-inserted plates, photomultiplier tube(PMT) and data-acquisition-system(NI-DAQ). When it centered on the plate was irradiated by proton, the generated signals were monitored by PC through PMT and DAQ. Detailed measurement position is flexibly changed depending on patient case by placing solid phantom between the plates. Initial multilayer-ADRS was consisted of 20 disks with the thickness and diameter of 2mm and 150mm, respectively having similar resolution to MLIC. New multilayer-ADRS with enhanced high-resolution was manufactured using 15 disks with thickness of 1mm. This study evaluated dosimetric characteristics of the 1mm-multilayer-ADRS with regard to response dose linearity, dose rate dependence, energy dependence and IDD profile.
Results: When proton beam was irradiated to 1mm disk, the signal size was 92.11 in 800V and suitable to discriminate between signal and noise. Irradiation with 50, 100, 200, 300, 500 and 700 cGy yielded the relative signals of 0.5, 1.0, 2.0, 3.0, 5.1 and 7.1, respectively. When 100 cGy were delivered at rates of 100 to 600 cGy/min, the signal was consistent with the standard deviation of 0.01. And the change of the signal with respect to the energy was nearby to zero. When IDD profile of 165.5MeV was measured using 2mm and 1mm multilayer-ADRS, uncertainty of range in comparison with commissioning data measured by bragg peak ion-chamber was 1mm and 0.4mm, respectively.
Conclusion: These results show Multilayer-ADRS has the advantages of high-efficiency, and low-cost, and also a significant potential as a new detector for PBS measurements.