Since their conception in the early 1990s, radioluminescence-based fibre-optic dosimeters (FODs) have attracted great interest for dosimetric applications in radiotherapy (RT). Over the years, many scintillating materials, both organic and inorganic, have been developed and tested by multiple research groups around the world. In parallel, reliable techniques for removing or subtracting the stem effect, one of the main drawbacks of FODs, have been proposed in the literature. To date, several prototype systems are widespread, some of which prove to be viable commercial solutions. This review aims to trace the efforts over the years that have enabled FODs to become reliable tools for dosimetry in the current RT procedures and promising options for future scenarios. After a first section devoted to a thorough discussion of the stem effect issue, the use of FODs in various applications of interest to RT, primarily small-field dosimetry and in vivo dosimetry, are addressed. Their use both in
This study investigates the use of a specially developed P-I-N diode to measure displacement damage in a silicon substrate caused by irradiation from 400 MeV/u 20Ne, 500 MeV/u 40Ar, 290 MeV/u 12C, and 6, 9, 12, 20 MeV electrons. Various energy levels of heavy ions attenuated by PMMA beam degraders were assessed. The study focuses on the forward voltage shift of the P-I-N diode as an indicator of displacement damage in silicon. Comparisons were made with simulated fluences, and the associated particle displacement Kinetic Energy Released per unit Mass (KERMA) to the silicon substrate.
The investigation revealed that the long base P-I-N diode's response is directly proportional to displacement damage, exhibiting a long dynamic range and independence from particle type, energy, and Linear Energy Transfer (LET). Applying a calibration factor demonstrated good agreement between simulation and experimental values. Diode fading was also assessed, showing a 20% voltage fade after several
This thesis aims to characterise the accuracy of a new active CMOS pad detector for dosimetry in HDR Brachytherapy. A 1x1x1 mm3 detector is doped with high resistivity n-type silicon, thickness of 100 μm (Wafer10) and 48 μm (Wafer20) epitaxial substrate and built in standard CMOS along with a transimpedance amplifier. This work investigates and examine this detector’s sensitivity and signal to noise ratio in air for use in High Dose Rate Brachytherapy (HDR BT) dosimetry. To understand operational characteristics of the detector, a current-voltage (I-V) characteristic curve was created, and the depletion voltage of the junction observed by using a Keithley Programmable Voltage Source to sweep the voltage and measure the current collected at the pad. Applying the established depleted voltage, the detector sensitive volume was tested by irradiating 5.5 MeV alpha beam with field size 1 mm x 1 mm at 1000 Hz event rate to observe the impact of radiation on the electronic and collection e
Background: In the Unity MR linac (Elekta AB, Stockholm, Sweden), the radiation beam traverses the cryostat and the coil support structure. The resulting beam attenuation must be considered for output calibration and its variation with gantry angle must be characterized in the treatment planning system (TPS). Purpose: The aim of this work was to investigate the impact of a change of the cryostat transmission characterization (CTC) curve, due to the helium level modification, on clinical treatment plan dosimetry and to report on the experience with the CTC curve update. Methods: Twenty stereotactic body radiotherapy (SBRT) treatment plans: 10 prostate and 10 oligo-metastatic cancer plans, prepared with a beam model incorporating the CTC curve acquired at installation time, were re-calculated using the model implementing CTC curve post helium top-up. To account for the CTC change as well as to align our system to the recent reference conditions recommendations, the new model was commissi
A large area pixelated silicon array detector named \MP987" has been developed for in-vivo dosimetry. The detector was developed to overcome the non-water equivalent response of EPID (Electronic Portal Imaging Device) dosimetry systems, due to the shortfalls of the extensive corrections required. The detector, readout system and software have all been custom designed and operate independently from the linac. The MP987 array is secured directly above the EPID, to be used in combination with the 6 MV imaging system.
During the course of this thesis many aspects of in-vivo dosimetry were looked at, including: electrical and dosimetric characteristics of silicon diodes, feasibility of a dual detector system, angular dependence of silicon and synthetic diamond detectors and the suitability of different detector readout systems for multichannel arrays in external beam radiotherapy.
In the final chapter of this thesis dosimetry characterisation measurements of percentage depth dose (PDD)