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Measurements of output factors using different ionization chambers and build up caps
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A. Iftikhar   |
| , iahmadmp@gmail.com |
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Abstract: (7521 Views) |
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Background: The aim of this work was to study
the output factors for Linac using different ionization
chambers and build up caps. Materials and Methods:
Output factors were measured for open square fields
(3 × 3 cm to 40 × 40 cm) defined by collimator jaws
for 6 and 15 MV photon beams from a Varian Clinac
2100C accelerator were measured. The measurements
in air were performed using Compact Cylindrical
and Farmer type ionization chamber fitted with
acrylic and brass build up caps. All measurements
were taken with the detector set with its central axis
perpendicular to the beam central axis and isocentrically
positioned at the reference depth in empty water
phantom. Results and Discussion: It was observed
that out put factors increased with field size for both
6 and 15 MV photon beams. The increase in output
factor is less prominent for brass build-up caps than
acrylic build up caps. Up to 1.53% and 0.97 %
difference were observed between 6 and 15 MV
energies for acrylic and brass build up caps respectively.
For acrylic build up cap, no significant
difference was found for both ionization chambers.
However, measurements for brass and acrylic build
up caps with same ion chamber differ by up to 4.4 %
for 15 MV energy. Conclusions: The measurement of
output factors Shwith cylindrical build-up cap made of
high Z material distorts Shand should be avoided. The
use of buildup caps with Zeff close to that of water
such as acrylic is a good choice. Ionization chamber is
the best choice for Sh measurements for large field
sizes. Iran. J. Radiat. Res., 2012 10(2): 95‐98
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| Keywords: Output factors, build up caps, ionization chamber |
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Full-Text [PDF 185 kb]
(6525 Downloads)
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Type of Study: Original Research |
Subject:
Radiation Biology
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