A tri-hybrid method to estimate the patient-generated scattered photon fluence components to the EPID image plane.

A tri-hybrid method to estimate the patient-generated scattered photon fluence components to the EPID image plane.
Phys Med Biol. 2020 Jun 09;:
Authors: Guo K, Ingleby H, Van Uytven E, Elbakri I, Van Beek T, McCurdy B
Abstract
In vivo dosimetry methods can verify the prescription dose is delivered to the patient during treatment. Unfortunately, in exit dosimetry, the megavoltage image is contaminated with patient-generated scattered photons. However, estimation and removal of the effect of this fluence improves accuracy of in vivo dosimetry methods. This work develops a 'tri-hybrid' algorithm combining analytical, Monte Carlo (MC), and pencil-beam scatter kernel methods to provide accurate estimates of the total patient-generated scattered photon fluence entering the MV imager. For the multiply-scattered photon fluence, a modified MC simulation method was applied, using only few histories. From each second and higher order interaction site in the simulation, energy fluence entering all pixels of the imager was calculated using analytical methods. For photon fluence generated by electron interactions in the patient (ie. bremsstrahlung and positron annihilation), a convolution/superposition approach was employed using pencil-beam scatter fluence kernels as a function of patient thickness and air gap distance, superposed on the incident fluence distribution. The total patient-scattered photon fluence entering the imager was compared wit...

Source: Physics in Medicine and Biology - June 8, 2020 Category: Physics Authors: Guo K, Ingleby H, Van Uytven E, Elbakri I, Van Beek T, McCurdy B Tags: Phys Med Biol Source Type: research