Centre for Medical Radiation Physics, Engineering Physics
Kelly, Andrew, Surface Dosimetry in Breast Radiotherapy, Masters thesis, Centre for Medical Radiation Physics, Engineering Physics, University of Wollongong, 2010. http://ro.uow.edu.au/theses/3816
Radiotherapy is a common tool used by clinicians in the treatment of breast cancer patients. This thesis investigates the calculation and measurement of phantom surface dose during an IMRT breast radiation therapy dose delivery.
Measurements were taken to prototype the MOSkin dosimeters placed on an anthropomorphic phantom. The dose measurements are also indicative of skin doses that patients are likely to receive with and without Orfit immobilisation cast material in place during radiation therapy.
The first part of this thesis is focussed on the beam modelling of the Pinnacle planning computer. In particular, it focusses on the ability of the planning system to accurately model a medical linear accelerator and calculate dose distributions in the build-up region. The reason this is relevant is because to date, planning system calculations are inaccurate in the build-up region, and calculated doses are thus discarded pieces of information. It was found that build-up dose calculations using a treatment planning system (TPS) could be improved by using Monte Carlo (MC) data as input to the beam modelling algorithm. These calculations were performed in cuboid phantom geometry as a precursor to curved contours.
The last part of this thesis investigates the dosimetric impact of using an immobilisation cast in breast radiotherapy. This study involved an anthropomorphic phantom and the use of EBT GafChromic film and MOSkins to investigate the magnitude of dose deposition at skin depth both with, and without, the Orfit immobilisation cast present. Dosimetric measurements were reported at numerous points of clinical interest to determine whether the Orfit immobilisation cast may be used in radiotherapy of the breast. Results show increases in dose to the breast surface, the clinical significance of which may be a matter for consideration by clinicians.