Highlights
- •Insufficient scattering material results in published Bw values that overestimate scatter.
- •An algorithm was developed for calculating backscatter in situations with reduced scattering medium.
- •Model validation by comparison with published data, Monte Carlo simulations and film measurements.
Abstract
Dosimetry protocols for superficial X-rays prescribe the determination of kerma on
the surface of a phantom through the use of a backscatter factor (Bw) that accounts for the effect of phantom scatter. Bw values corresponding to full-scatter phantoms are provided by these protocols. In
practice, clinical situations arise wherein there is insufficient scattering material
downstream, resulting in published Bw values that overestimate the amount of occurring scatter.
To provide an accurate dose calculation the backscatter values need to be corrected
for any reduction in scattered radiation. Estimating the change of Bw in situations with incomplete backscatter has previously been achieved by direct
measurements or Monte Carlo modelling. For increasing the accuracy of clinical dosimetries,
we developed a physical model to deduce an algorithm for calculating backscatter factors
in situations with reduced downstream scattering medium. The predictions of the model
were validated by comparison with published data, Monte Carlo simulations and film-based
measurements for beams with a half-value layer of 0.8, 2 and 4 mm Al.
Our algorithm accurately predicts the effect of partial scatter conditions with suitable
precision. Its reliability, combined with the simplicity of calculation, makes this
methodology suitable to be incorporated into routine clinical dosimetry. The algorithm’s
underlying physical model provides an intuitive understanding of the effects of field
size and beam energy on backscatter reduction, permitting a rational management of
this effect.
Keywords
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Article info
Publication history
Published online: September 05, 2019
Accepted:
August 23,
2019
Received in revised form:
May 29,
2019
Received:
January 28,
2019
Identification
Copyright
© 2019 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
