3D energy deposition measurements with the GEMPix detector in a water phantom for hadron therapy

J Leidner,A Rimoldi,A Tamborini,A Mirandola,M Ciocca,F Murtas,M Silari,S.P George

doi:10.1088/1748-0221/13/08/p08009

Abstract

In this paper we present 3D measurements of the energy deposition by a clinical carbon ion beam in a water phantom. Conventionally, these measurements are performed with an array of ionization chambers and used for quality assurance. The spatial resolution is typically not better than 5 mm. We used the GEMPix, a gaseous detector with a highly pixelated readout and much better spatial resolution. The GEMPix was obtained by coupling a triple Gas Electron Multiplier (GEM) to a quad Timepix ASIC with 512×512 pixels and 55 μm pitch. The Bragg curve, 2D images of the beam and a 3D reconstruction of the energy deposition are obtained from a single depth scan performed in approximately 15 minutes. A separate linearity check was also performed. The detector response is well linear and the measured Bragg curve is very smooth with uncertainties of a few percent. 3D energy deposition measurements in a water phantom with the GEMPix provide better spatial resolution than conventional devices. Systematic differences in the Bragg curve in comparison to the reference one are still too large for clinical use but work on several improvements is on-going.

Highlights

- Negative Ion Time Projection Chamber operation with SF6 at nearly atmospheric pressure E
Measurements of the current driven by the Gas Electron Multiplier (GEM) while performing a depth scan at CNAO provide a measurement of the Bragg curve: the current driven by the applied HV between the third GEM and the readout ASIC is proportional to the electrons multiplied in the GEMs
It has been shown that the GEMPix is capable of measuring the 3D energy deposition of a carbon ion beam in a water phantom. 2D images of the beam, the Bragg curve and the 3D reconstructed energy deposition can be obtained in a single depth scan that lasts about 15 minutes

Summary

Introduction

- Negative Ion Time Projection Chamber operation with SF6 at nearly atmospheric pressure E. : In this paper we present 3D measurements of the energy deposition by a clinical carbon ion beam in a water phantom. These measurements are performed with an array of ionization chambers and used for quality assurance. We used the GEMPix, a gaseous detector with a highly pixelated readout and much better spatial resolution. The GEMPix was obtained by coupling a triple Gas Electron Multiplier (GEM) to a quad Timepix ASIC with 512×512 pixels and 55 μm pitch. The Bragg curve, 2D images of the beam and a 3D reconstruction of the energy deposition are obtained from a single depth scan performed in approximately 15 minutes. The detector response is well linear and the measured Bragg curve is very smooth with uncertainties of a few percent

Methods

Findings

Discussion

Conclusion