F. Garciavicente et al., EXPERIMENTAL-DETERMINATION OF THE CONVOLUTION KERNEL FOR THE STUDY OFTHE SPATIAL RESPONSE OF A DETECTOR, Medical physics, 25(2), 1998, pp. 202-207
One of the most important parameters in the characterization of a dete
ctor is its spatial convolution kernel. This kernel contains all of th
e information about the influence that the detector size has on the me
asured beam profile. In this paper we present an experimental method f
or the determination of the spatial convolution kernel for commonly us
ed detectors that are employed in the x-ray profile measurement: filmdensitometer, diode, and ionization minichamber. Our work is based on
first assuming a step function pattern on a photographic film is known
and is a perfect step function, The kernel of the densitometer system
was then derived from the deconvolution of the scanned profile to the
step function. Next a film was exposed to a penumbra area of an x-ray
beam from a linac. The film was scanned using the same densitometer.
The ''real profile'' that emerges from a linear accelerator was derive
d by the deconvolution of the scanned profile using the now known kern
el of the film densitometer, Under the same irradiation condition the
x-ray profile was measured with other detectors and with this informat
ion we obtained the convolution kernels for these detectors by solving
numerically their basic convolution integrals. The results show that
the Gaussian convolution kernel is the most consistent with the measur
ements. The best numerical values for the FWHM of the kernels are 1.1
mm, 2.2 mm, and 5.4 mm for densitometer, diode, and minichamber, respe
ctively. (C) 1998 American Association of Physicists in Medicine.