SU-E-T-359: Forward / Backward Calibration and Clinical Application of a MLIC System for Uniform Scanning Proton Beam

Abstract

Purpose: To describe the successive calibration steps and applications in clinical environment of a multi‐layered ion chamber (MLIC) system for uniform scanning proton beam. Methods: The MLIC system contains 180 independent planar, parallel plate air vented chambers. The active collective area is defined by a circular surface of 2.5cm diameter. A dedicated electrometer was used to collect readable counts produced in the different chambers. Uniformly scanned proton beams with various ranges have been delivered to the device with field sizes of 10*10 [cm*cm] projected at the iso‐center. The material composition of the device has been chosen in order to present equivalent scattering properties to water. The Water Equivalent Thickness (WET) of the device was fine‐tuned and the channel to channel variation corrected following a forward and backward calibration strategy. Various Pristine and Spread Out Bragg peaks of several ranges and modulations have been measured and compared to reference water scans to validate the calibration method. Results: The characteristic analyses of Pristine and spread‐out Bragg peak measurements show that MLIC measurements are in good agreement with requested ranges and modulations within sub‐millimeter accuracy. Additionally the system allows to choose the appropriate time resolution in order to timestamp each layer individually and to proceed further with a detailed analysis of the irradiation delivery. Conclusions: MLIC measurements with WET and relative variation calibration show accurate and time‐saving depth dose measurements. It can be concluded that the use of such a device in overall reduces the overall time of the commissioning process down to ∼10% of the necessary time with standard Water Phantom equipment.