Comparison of measured and Monte Carlo-calculated peak scatter factors for 10X10 cm2 field size in 6 MV and 18 MV photon beams

The purpose of this thesis is to measure the peak scatter factors (PSFs) for a 10X10 cm2 field size in 6 MV and 18 MV photon beams using a Solid WaterTM phantom and build-up caps made of LuciteTM, aluminum, brass, and copper. The PSF for the 10X10 cm2 fie...

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Bibliographic Details
Main Author: Chung, Eunah
Other Authors: Ervin Podgorsak (Internal/Supervisor)
Format: Others
Language:en
Published: McGill University 2009
Subjects:
Online Access:http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=32261
Description
Summary:The purpose of this thesis is to measure the peak scatter factors (PSFs) for a 10X10 cm2 field size in 6 MV and 18 MV photon beams using a Solid WaterTM phantom and build-up caps made of LuciteTM, aluminum, brass, and copper. The PSF for the 10X10 cm2 field size was first determined by extrapolating the measured normalized peak scatter factor (NPSF) to 0X0 cm2 field size. The extrapolated NPSF was the reciprocal of the PSF(10, hv). The measured PSF(10, hv) was then compared to the PSF determined with Monte Carlo methods. We used Monte Carlo methods to investigate the dependence of the measured signal on the build-up cap material. This was carried out by calculating the primary and scatter dose contributions to the measured signal in the air cavity of the ionization chamber. Based on Monte Carlo studies, a factor was calculated to obtain the PSF from the measurements. === L'objectif de cette thèse est d'obtenir le peak scatter factor (PSF) de faisceaux de photons de 6 et 18 MV. Les champs utilisés étaient de 10x10 cm^2 et les mesures furent effectuées à l'aide d'un fantôme de Solid Water tm couplé à des capuchons d'accumulation fait de Lucite tm, d'aluminium, de laiton et de cuivre. Le PSF du champ de 10x10cm2 a été déterminé en extrapolant le peak scatter factor normalisé (NPSF) d'un champ de 0x0cm2. Le NPSF extrapolé correspond à la réciproque du PSF(10,hv). Le PSF(10, hv) fut ensuite comparé à celui déterminé à l'aide de méthodes Monte Carlo. Les méthodes Monte Carlo furent utilisées pour étudier la dépendance entre le signal mesuré et le matériel du capuchon d'accumulation. Ceci fut accompli en décomposant le signal provenant de la cavité de la chambre d'ionisation en dose primaire et diffusée. Un facteur liant le PSF et les mesures fut calculé à l'aide d'études Monte Carlo.