Radiation hardness of dsipm sensors in a proton therapy radiation environment

Abstract

Abstract-In vivo verification of dose delivery in proton therapy by means of positron emission tomography (PET) or prompt gamma imaging is mostly based on fast scintillation detectors. The digital silicon photomultiplier (dSiPM) allows excellent scintillation detector timing properties and is thus being considered for such verification methods. We present here the results of the first investigation of radiation damage to dSiPM sensors in a proton therapy radiation environment. Radiation hardness experiments were performed at the AGOR cyclotron facility at the KVI-Center for Advanced Radiation Technology, University of Groningen. A 150-MeV proton beam was fully stopped in a water target. In the first experiment, bare dSiPM sensors were placed at 25 cm from the Bragg peak, perpendicular to the beam direction, a geometry typical for an in situ implementation of a PET or prompt gamma imaging device. In the second experiment, dSiPM-based PET detectors containing lutetium yttrium orthosilicate scintillator crystal arrays were placed at 2 and 4 m from the Bragg peak, perpendicular to the beam direction; resembling an in-room PET implementation. Furthermore, the experimental setup was simulated with a Geant4-based Monte Carlo code in order to determine the angular and energy distributions of the neutrons and to determine the 1-MeV equivalent neutron fluences delivered to the dSiPM sensors. A noticeable increase in dark count rate (DCR) after an irradiation with about 10 8 1-MeV equivalent neutrons/cm 2 agrees with observations by others for analog SiPMs, indicating that the radiation damage occurs in the single photon avalanche diodes and not in the electronics integrated on the sensor chip. It was found that in the in situ location, the DCR becomes too large for successful operation after the equivalent of a few weeks of use in a proton therapy treatment room (about 5×10 13 protons). For PET detectors in an in-room setup, detector performance was unchanged even after an irradiation equivalent to three years of use in a treatment room (3 × 10 15 protons). Manuscript

A Review of Inorganic Scintillation Crystals for Extreme Environments

“…It has been estimated that a prompt gamma detector placed vertically at a distance of 30 cm from a 200-MeV proton beam is hit by 2 × 10 −5 neutrons/cm 2 /stopped proton [113]. In summary, assuming 380 patients/yr, the dose-verified detector should withstand at least fluences of 10 11 neutrons/cm 2 to operate without degradation for at least 5 yr [114]. Possible detector performance degradation due to these secondary neutrons, despite being a topic of relatively small interest, should not be overlooked when selecting scintillation crystals for proton therapy monitoring systems.…”

New Digital Plug and Imaging Sensor for a Proton Therapy Monitoring System Based on Positron Emission Tomography

“…It is a low photon flux silicon sensor with an area ranging typically between 1 mm 2 and 9 mm 2 and an internal gain of reached at a bias ranging between 20 V and 60 V. Modern commercially available SiPMs exhibit photon detection efficiency up to 40% at 420 nm and single photon time resolution less than 100 ps (FWHM) [ 32 , 33 , 34 ]. Radiation hardness is currently under investigation [ 35 ]. Due to their compact size and simple required readout electronics, they are substituting the traditional photomultiplier tubes in PET instrumentation for proton therapy monitoring systems.…”

Medical applications of silicon photomultipliers

“…Dendooven and coll. [68] have made an experiment with bare digital SiPMs to test the radiation hardness of such devices in a geometry configuration typical of in-beam PET operation. They found that the dark count rate (DCR) became too large for successful operation after the equivalent of a few weeks in a proton therapy treatment room (about 5 × 10 13 protons.…”