Date of Award

Fall 2012

Degree Type

Thesis

Degree Name

Master of Science (MSc)

Department

Medical Physics

Supervisor

Orest Ostapiak

Co-Supervisor

Kevin Diamond

Committee Member

Tom Farrell

Abstract

The purpose of this thesis is to explore the angular response to dose of the MatriXX Evolution, manufactured by IBA Dosimetry, a 2-dimensional ion chamber array used for patient specific quality assurance of advanced radiotherapy techniques such as IMRT and VMAT. Investigations were made to characterize the angular response of the MatriXX and describe any differences from the Philips Pinnacle3 Treatment Planning System (TPS) used at the Juravinski Cancer Centre.

A comparison was made between the gantry angle dependent correction factors supplied by the manufacturer and those derived by measurement. Gantry angle dependent correction factors were derived, with the MatriXX under 5cm polystyrene build-up and without any build-up, for the 5 x 5 cm2, 10 x 10 cm2 and 20 x 20 cm2 field sizes.

For gantry angles ranging from 320o to 40o the maximum difference between the derived gantry angle dependent correction factors and those provided by the manufacturer is 1.5%, at a gantry angle of 320o, a 5 x 5 cm2 field and without build-up. The differences for the 10 x 10 cm2 and 20 x 20 cm2 fields within this gantry angle range are less than 1%. Between gantry angles of 50o and 130o the largest difference is 4.9% at 100o, for the 5 x 5 cm2field without build-up. The other field sizes show similar differences; 4.7% at gantry angle of 120o for 10 x 10 cm2 with build-up and 4.0% at a gantry angle of 80o without build-up. Between gantry angles of 140o to 220o the greatest discrepancy is for the 5 x 5 cm2 field with build-up, a difference of 3.0%. The 10 x 10 cm2 has a maximum difference of 2.4% at gantry angles of 180o and 200o, both when the MatriXX has build-up. The maximum discrepancy for gantry angle dependent correction factors for the 20 x 20 cm2 fields is at a gantry angle of 140o, when the MatriXX has build-up. Between the gantry angles of 230o to 310o the largest discrepancy occurs between the derived gantry angle dependent correction factors and those supplied by the manufacturer. For the 5 x 5 cm2, 10 x 10 cm2 and 20 x 20 cm2 fields respectively the largest differences are 5.9%, 4.5% and 4.9%. All three occur when there is no build-up.

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