Evaluation of differences between measured and modeled properties of gamma camera in the dositest project

Abstract

Introduction To date, there is no standardized dosimetric protocol in molecular radiotherapy. Activity quantification based on scintigraphic imaging and cumulated activity calculation are still extremely different depending on the investigator centre they are coming from. The project DosiTest ( www.dositest.com ) aims at evaluating the impact of the wide heterogeneity of implemented dosimetric approaches by means of a virtual multi-centric inter-comparison based on Monte-Carlo simulation. In each clinical centre involved in the project, the gamma camera model, generated using GATE, has to be validated with experimental measurements. In this context, the objective of the present work is to optimize the protocol of acquisitions in order to limit discrepancies between measured and simulated characteristics of the camera. Materials and Methods The study was performed on a dual-head gamma camera Infinia from GE HealthCare equipped with a NaI (Tl) crystal of 3/8” (CHU Rangueil, Toulouse). For each head of detection, energy resolution, spatial resolution and sensitivity were determined based on national and international guidelines (IAEA, AAPM, SFPM) for both intrinsic and collimated configurations. The modelling step was done using the code Gate version 6.1, on computing cluster (480) or with GateLab environment. The geometry of experimental acquisitions was recreated in the virtual GATE space. Energy spectra are going to be repeated and a Kolmogorov– Smirnov analysis will be conducted on the whole spectrum and also on the photoelectric peak alone. Results/Perspectives Preliminary results show that the GATE simulation is running. However this step highlights some difficulties in modeling the back-compartment of the camera and the examination room where it is located. At this time of the study, repeated measurements for Technetium are under acquisition to establish ‘‘true” and optimized characteristics of the gamma camera. Additional acquisitions and modeling for Indium 111 will be performed quite soon in order to continue the dosimetric project of DosiTest.