High resolution polymer gel dosimetry for small and micro field dosimetry, and development of innovative polymer gel dosimeters
Creators: name: Wong, Christopher
Publisher: name: RMIT University
Year: 2024

description: Current radiotherapy techniques are focused on delivering effective treatments while sparing surrounding healthy tissues. As a result, radiotherapy treatments are using narrower and more tightly conforming therapy techniques. For these treatments to be effective an accurate measure of the dose delivered by these very narrow radiotherapy beams, both in and around the target volume, is required. It is a challenging task for the conventional type dosimeters to determine dose distribution in such small fields. The best example of such fields is microbeam beam radiotherapy (MRT), a developing treatment technique that takes this requirement even further. MRT delivers an array of micrometre size radiotherapy beams to the target. MRT has been shown to be highly effective, but reliable dosimetry of MRT is challenging due to the micrometre scales involved. Attempts to determine the MRT do se distribution have been documented for using special type dosimeters such as radiochromic film and MOSFET detectors, as well as Monte Carlo simulations. <br><br>This thesis investigates polymer gels as a dosimeter for dose distribution measurements of small radiotherapy fields and microbeams. Polymer gel dosimetry is a technique which uses a tissue-equivalent gel to act as both a three-dimensional dosimeter and a phantom at the same time. These gels polymerise when exposed to ionising radiation and the response is locally dose dependent linearly. <br><br>This thesis investigates the use of polymer gels for the dosimetry of small sub-centimetre (down to 3 × 3 mm2) and micrometre radiotherapy fields. A high resolution imaging technique is also required for such small beam dosimetry. This work used special high strength MRI scanners to analyse polymer gels at high resolution. This work explores the feasibility of polymer gels irradiated by microbeams and analysed using Raman spectroscopy as a dosimeter for synchrotron generated microbeams. MRT is characterised by very high doses, and special high-dose resistive types of gel were developed as part of this work. It is shown that polymer gels imagined using Raman spectroscopy techniques are capable of measuring the dose distribution of microbeam radiation techniques. <br><br>This thesis also investigates the use of polymer gels to measure dose perturbations caused by metallic artefacts. Metallic artefacts, such as a surgical aneurysm clip, can be left in a patient and cause dose perturbations during radiotherapy procedures. Polymer gels were used to determine the degree of dose enhancement induced by an aneurysm clip placed inside when irradiated with a typical stereotactic radiotherapy procedure. <br><br>In addition, this thesis used gels in several other innovative applications. Photonuclear interactions generated in gel by high energy x-ray beams were measured via secondary neutrons. Special clear-type gels that do not change colour with irradiation were developed. Polymer gels were investigated for dosimetry of an extremely high dose rate capacitor type linear accelerator. And polymer gels were for measurement of a high energy proton beam.