A Dissertation submitted to the faculty of science, University of the Witwatersrand,
Johannesburg, in fulfilment of the requirements for the degree of Master of Science.
May 2016 / The multileaf collimator (MLC) system introduction into clinical linear
accelerators (Linacs), facilitated computer-control and verification of complex treatment, and
results in an increase in patient set up speed. An MLC system thus requires a re-evaluation of
the quality assurance (QA) requirements for beam collimation. This study investigated,
developed, performed and evaluated QA effors for conventional MLCs with the aim to
evaluate the efficacy and reproducibility of the quality control (QC) procedures with different
The performance of MLCs for an Elekta (Livingstone hospital)
and siemens (Charlotte Maxeke Johannesburg academic hospital) linac were examined.
The major QC procedures studied were leaf matching, leaf position accuracy, intraleaf
leakage and transmission through abutting leaves. Three portal imaging devices
(radiographic film, radiochromic film and an electronic portal imaging device) and a PTW
LA48 linear array were used as detectors. Record and verify data management systems were
used to set up and execute the procedures. The calibration of all the potal imaging devices
was also performed.
The calibration procedure of the portal imaging devices is linac specific in execution.
The profiles obtained indicated consistency across device and time. A combined single
execution procedure is viable and reproducible on all platforms.
The results show tha the calibration of imaging devices is of great importance. The MLC
design influences the range and extent of QC that can be performed. This may impact on
the accuracy with advanced technologies requiring high conformity and reproducible leaf
movement, can be deliverd. Imaging devices each have specific resource requirement issues
affecting the efficacy of their use.
|Date||14 September 2016|
|Creators||Rule, Ayron Edward|
|Source Sets||South African National ETD Portal|
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