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Energy Spectrum Inference of Clinical Photon Beam by Use of PDD


J Kotoku

J Kotoku1*, A Haga2, S Kumagai1, N Saotome2, T Kobayashi1, (1) Teikyo University, Tokyo, Japan,(2) University of Tokyo Hospital, Tokyo, Japan

MO-D-108-3 Monday 2:00PM - 3:50PM Room: 108

Purpose:
To propose a scheme which infers an energy spectrum of X-ray from a Linac by use of percent depth dose with an ion chamber.

Methods:
In this study, we assumed a linear model which relates the spectrum of clinical photon beam and percentage depth dose of the beam.The response matrix (design matrix) was calculated via our Monte Carlo simulation (EGS5).
Then we estimated the photon spectrum as a solution of maximum a posteriori (MAP) estimation.
The percent depth dose of 4MV X-ray was measured with an ion chamber and 3D water phantom in Teikyo University Hospital.

Results:
Both estimated spectrum and modeled spectrum in the commercial treatment planning system are in good agreements.
It is evident that our inference method is very effective and powerful to estimate the X-ray energy spectrum.
Although this is an only case to infer the energy spectrum of clinical photon beam,
The success indicates an effectiveness of our method.

Conclusion:
A Bayesian method to infer an energy spectrum of clinical photon beam by use of a percentage depth dose was proposed and validated.

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