Year

2020

Degree Name

Doctor of Philosophy

Department

School of Physics

Abstract

Accurate empirical modelling of the treatment beam is necessary to ensure accurate delivery of dose to the intended target site. Dose calculations within the treatment planning system (TPS) for Stereotactic Radiosurgery (SRS) and Stereotactic Radiotherapy (SRT) treatment rely upon accurate beam data. Inaccuracies within the empirical measurements will propagate as errors throughout calculated patient dose distributions (Tyler, 2013). The necessary empirical measurements for beam commissioning include: percentage depth dose (PDD), output factor (OF) and beam profiles. Thus, especially for the consideration of the afore mentioned small radiation fields, it is important to ensure the most appropriate detector is chosen to conduct measurements of the treatment beams to achieve the highest possible accuracy in measurement of beam parameters.

Stereotactic Body Radiation Therapy (SBRT) requires precise delineation of the target using modern imaging modalities (MRI, CT etc.), accurate dosimetry to ensure the planned dose is delivered correctly and effective patient immobilisation. For extracranial sites the treatment accuracy is affected by tumour delineation which identifies the extent of the tumour volume and tumour motion resulting from the physical, biological and physiological processes of the human body. Delivery of radiation using highly conformal and small radiation beams presents challenges for dosimetry and quality assurance (Heydarian, 1996), (Das, 2008). To correctly measure dose in a small field an ideal dosimeter must exhibit properties including: small sensitive volume, near water equivalence, minimal beam perturbation and no dose-rate, energy or directional dependence (Pappas, 2008). Also, treatment planning for dose calculation must be conducted using algorithms which can account for the impact of the heterogeneities found in the abdomen and thoracic cavities to ensure calculation of the dose to tissue in regions with complex scattering conditions is accurate (Rubio, 2013).

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.