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Title: Monte Carlo modelling for radiotherapy
Author: Lewis, R. D.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2000
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The Monte Carlo code MCNP-4B has been utilised to investigate the origins of radiation dose perturbation in the head and neck region, arising from natural heterogeneities, the changing external contours of the patient, boundaries between materials of different atomic number and prosthetic implants. MCNP-4B was used to develop a simple model of a linear accelerator treatment head which incorporated the electron target, primary collimator, beam flattening filter and the secondary collimators. The model was used to calculate the energy spectra and angular distribution of the x-ray beam from a 4 MV Philips SL 75/5 and a 10 MV SL 15, and then tested by using these data to compute the central and off-axis x-ray beam profiles for various field sizes in water. Monte Carlo simulations using the calculated spectra were used to assess the dose distribution of treatment plans obtained in a simple heterogeneous phantom by several commercially available treatment planning systems. Practical measurements were undertaken using film dosimetry. The dose distributions were calculated for a variety of irradiation conditions designed to show the effects of surface obliquity, inhomogeneities and missing tissue above tangential beams. The results show maximum differences of 47% between some planning algorithm and film. Overall, the dose distribution obtained from film was most faithfully reproduced by the MCNP. The dose due to backscatter and lack of forward scatter from a metal implant within a head and neck phantom has been shown vary with atomic number, field size, surface obliquity, implant thickness, variations in secondary electron transport and the presence of teeth.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available