Designing Optimal Bias Voltage for Radiotherapy Diamond Dosimeter

Document Type: Conference Proceedings

Authors

1 Biomedical Engineering and Medical Physics Department, Shahid Beheshti University of Medical Sciences, Tehran, Iran

2 Medical Physics Department, Faculty of Medicine, Mashhad University of Medical sciences, Mashhad, Iran

3 Atomic and Molecular Physics Department, Yazd University, Yazd, Iran

Abstract

Introduction: Recent developments of radiotherapy techniques, require high accuracy detectors to determine the delivered dose in a small area. Chemical vapor deposition (CVD) or naturally growth diamond detectors which are commercially available are good candidates for this purpose. In these detectors two electrodes with high different electrical potential are deposited on both sides of a diamond, and the incident radiation generates a current which indicates absorbed dose. However, the large band gap makes diamond an excellent electrical insulator, but care must be taken to eliminate the air ionization contribution to the photocurrent. For this reason, the device must operate in vacuum. In the other hand, patient’s safety needs a decrease in detector’s voltage. In this simulation study, it is indicated that the applied voltage can be decreased to about 50[V] without loss of dosimeter’s sensitivity.
Materials and methods: In this work Weightfield2 software, which is a program to simulate current signals in a silicon or diamond detector was used. This program uses GEANT4 libraries to simulate the energy released by an interacting particle. Minimum Ionizing Particle (MIP) with a 250 micrometers thick pure diamond was used and then the bias voltage was increased from 1 [V] to 500 [V], then the curve of time response and current response of the sensor was observed as a function of bias voltage.
Results: The results indicate that the applied voltage can reduce up to about 50 [V] with a reasonable 40 [ns] time response. This can be achieved by the benefit of high accuracy and fast Analog to Digital Converters (ADCs).
Conclusion: With new generation of synthetic diamonds known as single crystal CVDs, which their characteristic is very similar to natural diamond, and with modern electric measuring devices, in contrast to the current sensors, it is possible to reduce the applied voltage of dosimeter electrodes to about 50 [V].

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