Effects of Temperature and X-rays on Plastic Scintillating Fiber and Infrared Optical Fiber

In this study, we have studied the effects of temperature and X-ray energy variations on the light output signals from two different fiber-optic sensors, a fiber-optic dosimeter (FOD) based on a BCF-12 as a plastic scintillating fiber (PSF) and a fiber-optic thermometer (FOT) using a silver halide optical fiber as an infrared optical fiber (IR fiber). During X-ray beam irradiation, the scintillating light and IR signals were measured simultaneously using a dosimeter probe of the FOD and a thermometer probe of the FOT. The probes were placed in a beaker with water on the center of a hotplate, under variation of the tube potential of a digital radiography system or the temperature of the water in the beaker. From the experimental results, in the case of the PSF, the scintillator light output at the given tube potential decreased as the temperature increased in the temperature range from 25 to 60 °C. We demonstrated that commonly used BCF-12 has a significant temperature dependence of −0.263 ± 0.028%/°C in the clinical temperature range. Next, in the case of the IR fiber, the intensity of the IR signal was almost uniform at each temperature regardless of the tube potential range from 50 to 150 kVp. Therefore, we also demonstrated that the X-ray beam with an energy range used in diagnostic radiology does not affect the IR signals transmitted via a silver halide optical fiber

Effects of Temperature and X-rays on Plastic Scintillating Fiber and Infrared Optical Fiber

In this study, we have studied the effects of temperature and X-ray energy variations on the light output signals from two different fiber-optic sensors, a fiber-optic dosimeter (FOD) based on a BCF-12 as a plastic scintillating fiber (PSF) and a fiber-optic thermometer (FOT) using a silver halide optical fiber as an infrared optical fiber (IR fiber). During X-ray beam irradiation, the scintillating light and IR signals were measured simultaneously using a dosimeter probe of the FOD and a thermometer probe of the FOT. The probes were placed in a beaker with water on the center of a hotplate, under variation of the tube potential of a digital radiography system or the temperature of the water in the beaker. From the experimental results, in the case of the PSF, the scintillator light output at the given tube potential decreased as the temperature increased in the temperature range from 25 to 60 °C. We demonstrated that commonly used BCF-12 has a significant temperature dependence of −0.263 ± 0.028%/°C in the clinical temperature range. Next, in the case of the IR fiber, the intensity of the IR signal was almost uniform at each temperature regardless of the tube potential range from 50 to 150 kVp. Therefore, we also demonstrated that the X-ray beam with an energy range used in diagnostic radiology does not affect the IR signals transmitted via a silver halide optical fiber

2D Monolithic silicon detectors for dosimetry in Small beam radiotherapy (Stereotactic Radiotherapy)

Radiation Therapy is one type of cancer’s treatment, which aims to kill or control tumour cells by using high energy radiation. However, it can affect both normal and tumour cells. Due to that, scientists worked to develop a new treatment technique of radiation delivery that focuses the high prescribed dose on the small localized area of tumour cells and protects the normal cells. This focal irradiation technique is called Stereotactic Radiosurgery (SRS). Using SRS allows the treatment of hard-to-reach lesions where surgery is not possible because of the risks resulting in the surgical procedures. The commissioning and Quality Assurance of SRS/SRT is complex and requires special dosimetry tools. Poor dosimetry of small-field characteristics may lead to reduced treatment efficacy, whether by under-dosage of targeted tumours or overirradiation of adjacent healthy tissues. Poor measurements of the small field characteristics, such as FWHM, penumbra width, output factors and percentage depth dose may result in pernicious health consequences, such as radiation-induced carcinogenesis. Hence, the dosimetry tool plays an important role in the SRS/SRT accuracy and precise delivery. Recently, silicon detectors have increased in popularity because they have high spatial resolution, small sensitive volume, high sensitivity to radiation, reasonable uniformity and provides real time measurements. The Centre for Medical Radiation Physics (CMRP) has developed two innovative monolithic silicon array detectors, DUO and OCTA, to be used in SRS/SRT for pretreatment quality assurance dosimetry. Therefore, the aim of this thesis is to characterise these two monolithic silicon detectors for small radiation field dosimetry employed in stereotactic radiotherapy