First full-beam PET acquisitions in proton therapy with a modular dual-head dedicated system

G Sportelli,K Straub,A Kraan,A Tramontana,J E Ortuño,G A P Cirrone,G Cuttone,F Romano,N Belcari,A Santos,A Del Guerra,S Ferretti,V Rosso,N Camarlinghi

doi:10.1088/0031-9155/59/1/43

Abstract

During particle therapy irradiation, positron emitters with half-lives ranging from 2 to 20 min are generated from nuclear processes. The half-lives are such that it is possible either to detect the positron signal in the treatment room using an in-beam positron emission tomography (PET) system, right after the irradiation, or to quickly transfer the patient to a close PET/CT scanner. Since the activity distribution is spatially correlated with the dose, it is possible to use PET imaging as an indirect method to assure the quality of the dose delivery. In this work, we present a new dedicated PET system able to operate in-beam. The PET apparatus consists in two 10 cm × 10 cm detector heads. Each detector is composed of four scintillating matrices of 23 × 23 LYSO crystals. The crystal size is 1.9 mm × 1.9 mm × 16 mm. Each scintillation matrix is read out independently with a modularized acquisition system. The distance between the two opposing detector heads was set to 20 cm. The system has very low dead time per detector area and a 3 ns coincidence window, which is capable to sustain high single count rates and to keep the random counts relatively low. This allows a new full-beam monitoring modality that includes data acquisition also while the beam is on. The PET system was tested during the irradiation at the CATANA (INFN, Catania, Italy) cyclotron-based proton therapy facility. Four acquisitions with different doses and dose rates were analysed. In all cases the random to total coincidences ratio was equal or less than 25%. For each measurement we estimated the accuracy and precision of the activity range on a set of voxel lines within an irradiated PMMA phantom. Results show that the inclusion of data acquired during the irradiation, referred to as beam-on data, improves both the precision and accuracy of the range measurement with respect to data acquired only after irradiation. Beam-on data alone are enough to give precisions better than 1 mm when at least 5 Gy are delivered.

Highlights

Dose range in proton therapy is subject to several sources of uncertainty, including the incompleteness of physical models (Pia et al 2010) and the effects of registration and patient movement (Hui et al 2008)
In the following we present the first reconstructed positron emission tomography (PET) images of the activity produced during the continuous irradiation of a polymethyl methacrylate (PMMA) phantom at the CATANA cyclotron-based proton therapy facility
A set of PET measurements was performed at the cyclotron-based proton therapy facility at CATANA, during the irradiation of a PMMA phantom at different dose rates and stopping the acquisition 10 min after

Summary

Introduction

Dose range in proton therapy is subject to several sources of uncertainty, including the incompleteness of physical models (Pia et al 2010) and the effects of registration and patient movement (Hui et al 2008). An in vivo monitoring would allow better treatment planning by assuring the detection of discrepancies between the planned and the actual delivery close to critical organs It could support experimental activities for better understanding uncertainties and their sources, contributing to increase the reliability of safety margins and eventually to enhance the number and diversity of beam directions

Methods

Results

Conclusion