Tahmasebi Birgani M, Behrooz M, Shahbazian H, Shams A. Determination of the attenuation coefficient for megavoltage photons in the water phantom. Int J Radiat Res 2012; 9 (4) :251-255
URL:
http://ijrr.com/article-1-819-en.html
, tahmasebi_mj@yahoo.com
Abstract: (9343 Views)
Background: Attenuation coefficient (μ) plays an
important role in calculations of treatment planning
systems, as well as determination of dose distributions
in external beam therapy, dosimetry, protection,
phantom materials and industry. So, its exact
measurement or calculation is very important. The
aim of this study was to evaluate the μ in different
points in the water phantom analytically as a formula,
in addition to derive and parameterize it with
dosimetry measurements data results. Materials and
Methods: To find the attenuation coefficients at each
point along the central axis of the beam in the
phantom for every size of the fields, the first mathematical
approach was performed for derivation of μs
from percentage depth dose (PDD) formula. Then by
dosimetry for different fields in different depths of
water phantom, one can parameterize the obtained
formula for μ in any field and depth. Results: By
comparing the mathematical and dosimetry results,
the parameters of the μ-expression were derived in
terms of the dimension of square field in different
depths. From this formula one can find the μ for any
field in different depths for two energies of the Varian
2100CD linear accelerator, 6, 18MV with the
statistical coefficient of determination of R2>0.98.
Conclusion: The measurement of the μ in each field
size and depth has some technical problems, but one
can easily measure the μ for every point of central
axis of the beams in any field size. Iran. J. Radiat. Res.,
2012 9(4): 251-255
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