A study to assess and improve dose computations in photon beam therapy

• Main Author: Aspradakis, Maria M
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1997
• Subjects: Nursing

This thesis is concerned with the calculation of dose at a point for megavoltage photon therapy. The review of dose calculation algorithms provides a comprehensive and critical analysis of the models developed to date. Emphasis is given to the dimensionality of density information utilised by these algorithms in relation to their capability of producing accurate dose information in three dimensions. Two applications of the Monte Carlo method to radiotherapy have been studied. Namely, the generation of energy deposition kernels (EDK) and the use of the method as a benchmarking tool. EDKs represent the fractional energy deposited around a single photon interaction site. Dose distributions in homogeneous and heterogenous media were calculated in absolute units of absorbed dose per incident photon fluence (Gy . cm2). Both applications were carried out using the EGS4 code system. A superposition model was developed from the dose deposition point of view. Dose at a point was obtained from knowledge of the total energy released per unit mass in the medium (TERMA) and the EDK. Effective energy spectrum information was used to calculate dose for clinical beams. The performance of this model was verified in homogenous and heterogeneous media against both Monte Carlo generated and measured data. The necessity for computation speed is addressed. As a trade off between accuracy and speed, a method was developed which reduces the calculation time required to obtain a true three dimensional dose matrix.