Year

2016

Degree Name

Doctor of Philosophy

Department

School of Physics

Abstract

During the past years, radiotherapy has become a widely used technique for treatment of tumors on different areas of the human body. The evolution of the technology has led to the necessity to assure the safety of the patient at any time during any kind of treatment. A wide range of instrumentation has been developed to perform a state of art dosimetry for the Quality Assurance (QA) of the irradiating beam. Tumors can be treated using different methodologies, depending on their position and dimension. The radiation techniques have been classified in three major groups: Microbeam Radiation Therapy (MRT), Brachytherapy and External Beam Radiation Therapy (EBRT). Each of them presents different characteristics in terms of intensity of delivered dose, timing and speed of the irradiation. The aim of this research project is to study and design a unified Data Acquisition system (DAQ) able to monitor and measure the irradiating beam of any of the three clinical scenarios. A DAQ is a very complex system comprising multiple aspects. It can be divided in four main sections: detectors, the sensitive part; electronic and analogue front end; digital core and Graphical User Interface. The goal to create a unified dosimetry platform has been achieved by the design of a modular read out electronic section and a modular digital core, which can be easily adapted to the different detectors and analogue front ends. The project started with the development of a single channel DAQ to read out a single microstrip diode for MRT application. The goal of the DAQ was to have high spatial resolution, to resolve a 50 μm wide microbeam, and a large sensitivity range. In fact, for this application, the beam instead of being flat has very narrow peaks where high radiation dose is delivered, spaced by areas where radiation is very low or none (named valley). Then the system has been upgraded into a multi-channel DAQ able to acquire a 128 diodes array for Brachytherapy treatments. In this scenario, the source moves during the treatment and can be placed far away from the detector. By using an array of diodes, the system has been able to reconstruct the movement of the source at any time during the treatment. A new high sensitivity front end has been introduced to perform dosimetry up to 12 cm distance from the irradiating source. The same DAQ has been used in multi-channel configuration for EBRT treatments and its modular design allowed the introduction of larger detectors, up to 512 channels, to best suit each different application. Moreover, the flexible timing constraints of the front-end used to read out the detector, allowed the setup of a triggered acquisition which can be synchronized with the LINAC beam to have a highly efficient dosimetry measure. Lately, a new standalone section has been introduced: it comprises a rotatable phantom and its movement control. It features an inclinometer, which detects the position of the LINAC gantry, and a control system made by an encoder and a stepper motor to align the detector to the gantry. This setup is particularly useful for application like VMAT and IMRT, where the treatment is delivered by rotating the LINAC around the patient and it is also compatible with all the previously developed DAQ.

Overall this research project has given a relevant contribution to the development of a unified platform for advanced radiation dosimetry. The outcome is a modular DAQ whose setup can be chosen to best suit each particular application. Even if the DAQ can be improved and upgrades are already undergoing feasibility studies, this research study has contributed to the publication of many peer reviewed papers internationally recognized.

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