Characterization of small high energy proton beams in homogenous and heterogenous media
Abstract
This thesis advances the study of small high energetic photon fields in radiotherapy. Small photon field irradiation is aimed at delivering a uniform dose to a well defined target while minimizing the dose to the surrounding normal tissue. The dosimetry of small x-ray fields is complicated by two factors: the relationship between detector size and field dimensions and the lack of equilibrium in lateral charged particles. Additionally, a longitudinal charged particle disequilibrium is present when materials with different atomic composition and density than water are introduced in a water-like phantom. , Small radiation dosimeters such as diamond, diodes film and a mini-ion chamber have a better spatial resolution to detect the steep dose fall-off at the edge of small photon fields than the large Markus chamber. The line spread function (LSF) of the film densitometer can be estimated by simple measurement of a slit image. Deconvolution of the measured, beam profile from a linear accelerator (linac) with the LSF of a detector yields an estimate of the true inherent beam profile of the linac. Conversely, the LSF of any detector can be estimated by deconvolution from measured data once the inherent profile is known. Similarly, a blurring function representing the finite source size effect of the head of the linac which is missing in a Monte Carlo simulation can be obtained. Because the deconvolution process is highly sensitive to noise, the Total Least Squares (TLS) approach…
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