An Evaluation of Bipolar Junction Transistors as Dosimeter for Megavoltage Electron Beams

Conference · Wed Jul 01 00:00:00 EDT 2015

OSTI ID:22531378

Passos, Renan Garcia de; Vidal da Silva, Rogerio Matias; Silva, Malana Marcelina Almeida; Souza, Divanizia do Nascimento ^[1]; Pereira dos Santos, Luiz Antonio ^[2]

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1. Departamento de Fisica, Universidade Federal de Sergipe, Av. Marechal Rondon, sn, Sao Cristovao, SE, 49100-000 (Brazil)
2. Comissao Nacional de Energia Nuclear, CNEN/CRCN-NE, Av. Prof. Luiz Freire, 1, Recife, PE, 50740-540 (Brazil)

Dosimetry is an extremely important field in medical applications of radiation and nowadays, electron beam is a good option for superficial tumor radiotherapy. Normally, the applied dose to the patient both in diagnostic and therapy must be monitored to prevent injuries and ensure the success of the treatment, therefore, we should always look for improving of the dosimetric methods. Accordingly, the aim of this work is about the use of a bipolar junction transistor (BJT) for electron beam dosimetry. After previous studies, such an electronic device can work as a dosimeter when submitted to ionizing radiation of photon beam. Actually, a typical BJT consists of two PN semiconductor junctions resulting in the NPN structure device, for while, and each semiconductor is named as collector (C), base (B) and emitter (E), respectively. Although the transistor effect, which corresponds to the current amplification, be accurately described by the quantum physics, one can utilize a simple concept from the circuit theory: the base current IB (input signal) is amplified by a factor of β resulting in the collector current IC (output signal) at least one hundred times greater the IB. In fact, the BJT is commonly used as a current amplifier with gain β=I{sub C}/I{sub B}, therefore, it was noticed that this parameter is altered when the device is exposed to ionizing radiation. The current gain alteration can be explained by the trap creation and the positive charges build up, beside the degradation of the lattice structure. Then, variations of the gain of irradiated transistors may justify their use as a dosimeter. Actually, the methodology is based on the measurements of the I{sub C} variations whereas I{sub B} is maintained constant. BC846 BJT type was used for dose monitoring from passive-mode measurements: evaluation of its electrical characteristic before and after irradiation procedure. Thus, IC readings were plotted as a function of the applied dose in 6 MeV electron beam from a linear accelerator, Clinac iX. The results show that this new methodology could be an alternative to study the dose in superficial tumors in radiation oncology. (authors)

• Research Organization: Institute of Electrical and Electronics Engineers - IEEE, 3 Park Avenue, 17th Floor, New York, N.Y. 10016-5997 (United States)
• OSTI ID: 22531378
• Report Number(s): ANIMMA-2015-IO-330; TRN: US16V0423102319
• Resource Relation: Conference: ANIMMA 2015: 4. International Conference on Advancements in Nuclear Instrumentation Measurement Methods and their Applications, Lisboa (Portugal), 20-24 Apr 2015; Other Information: Country of input: France
• Country of Publication: United States
• Language: English

Related Subjects

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
61 RADIATION PROTECTION AND DOSIMETRY
62 RADIOLOGY AND NUCLEAR MEDICINE
AMPLIFIERS
CIRCUIT THEORY
DOSEMETERS
DOSIMETRY
ELECTRON BEAMS
GAIN
INJURIES
IRRADIATION PROCEDURES
JUNCTION TRANSISTORS
LINEAR ACCELERATORS
MEV RANGE
MONITORING
NEOPLASMS
PATIENTS
PHOTON BEAMS
QUANTUM MECHANICS
RADIOTHERAPY
SEMICONDUCTOR JUNCTIONS
SEMICONDUCTOR MATERIALS
TRAPS