الفهرس 
INTRODUCTION AND AIM OF THE WORKOnly 14 pages are availabe for public view
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Abstract
Development of digital linear accelerators of moving
multileaf collimator with arc mode has given a new dimension to
radiation dose delivery. This technology is known as Dynamic Arc
Therapy (DAT) and recently implemented in many of the clinical
sites. The present proposed protocol describes a quality assurance
(QA) tests on both static multileaf collimator (SMLC) and dynamic
multileaf collimator (DMLC) for Dynamic Arc Therapy techniques.
Visual and qualitative analyses of the leaf positioning accuracy
according to the acceptable limits will be inspected. The stability of
DMLC will be analyzed qualitatively and quantitatively using film
dosimetry. The protocol will also summarize the systematic
procedure and sequence of tests aiming to have a complete guide to
the radiotherapy physicists for the QA of the DMLC with Dynamic
Arc Therapy. The SMLC leaf positions were developed a robust,
accurate and generic algorithm to measure the individual static
MLC leaf positions. This was performed by extracting leaf tip
locations from the radiographic film image and measuring their
relative distance from a reference line on the film. The reference
line was created with a selected set of MLC leaf sides. The film
scaling was created and verified using the physical leaf width. The
average measured distance corresponds to a leaf width of 10.0 mm
was 9.95 ± 0.09 mm. The estimated reproducibility of the leaf tips
location was ± 0.26 mm. The code accuracy was checked by
intentionally positioning set of leaves with small errors (1.0 mm),
and the detected deviations from the expected positions within the
range from -0.25 mm to +0.32 mm. The algorithm includes two self
testing functions in order to detect failures of leaf positioning due
to poor film quality and to avoid the potential systematic errors
attributable to the improper collimator setting. The code is
promising to be more efficient with Gafchromic film and electronic
portal image device (EPID).
Abstract
XIX
In this study, assessment of the dynamic MLC performance
was based on the evaluation of sliding gaps traveling across the
field in different conditions in both gantry-fixed and arc modes
which may affect the stability of MLC speed during gantry rotation.
The sliding gap test was sensitive to small changes in leaf position
and speed across the range of the leaf travel which could be
affected by motor fatigue.
In the present work the following QA of DMLC tests were
performed:
(1) Leaf speed stability test (multi-travel test) is performed
to check the stability of the leaves motion with different speeds
with a fixed gantry angle of zero as well as with arcs. The average
of passed gamma values using 2%DD and 2.0 mm DTA criteria
was above 98.80 % for all film irradiations except for the
comparison between them and the absolute one (14×14 cm2) was
87.14%.
(2) Oscillating sweeping gap test, different uniform MLC
gap is moving repeatedly back and forth across the field at a
constant speed during a fixed gantry angle of zero as well as full
arcs. The average of passed gamma values using 2%DD and 2.0
mm DTA criteria was 90.93 % for all film irradiations.
(3) Garden fence test, very small band moving across the
field with stopping movement at defined positions during
irradiation to create fences at fixed gantry angles (0°, 90°, 180°,
and 270°) and arc mode. The average fraction of passed gamma
values using 3%DD and 3.0 mm DTA criteria was above 96.74 %
for all films except for the comparisons between gantry angle 0°
with 270°, and 90° with 270° which yielded 91.15% and 90.12%
respectively.
Those new dynamic tests are better may be quick
consistency test without comprehensive analysis. The elements
which have been quantitatively investigated are: the accuracy and
stability of MLC leaf gap width and their resulting; and the speed
of each leaf over the whole range of its positions. The ultimate aim
Abstract
XX
of this study is to develop and implement faster, easier, and more
accurate QA techniques for MLC performance and helps in faster
troubleshooting of MLC problems in both static and dynamic QA.
The present QA applied protocol, based on the obtained
results, had minimized both time taken during operations and
money spend to buy expensive analysis software.
Accordingly, static multileaf collimator (SMLC) and
dynamic multileaf collimator (DMLC) for Dynamic Arc Therapy
techniques have replaced as the standard quality assurance (QA) for
linear accelerator machines in our department. These techniques
were useful to be investigated by another material using
Gafchromic and EPID