Encrypted login | home

Program Information

The Volume Effect Correction of Probe-Type Dosimetric Detectors Derived From the Convolution Model

no image available
H Looe

HK Looe1*, B Poppe1 , D Harder2 (1) Pius Hospital and Carl von Ossietzky University, Oldenburg, Germany, (2) Georg August University, Goettingen, Germany


SU-E-T-328 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To derive and introduce a new correction factor kV, the "volume effect correction factor", that accounts for not only the dose averaging over the detector's sensitive volume but also the secondary electron generation and transport inclusive of the disturbance of the field of secondary electrons within the detector.

Materials and methods:
Mathematical convolutions and Fourier's convolution theorem have been used. Monte Carlo simulations of photon pencil beams were performed using EGSnrc. Detector constructions were adapted from manufacturers' information.

For the calculation of kV, the three basic convolution kernels have to be taken into account: the dose deposition kernel KD(x) (fluence to dose), the photon fluence response kernel KM(x) (photon fluence to detector signal) and the "dose response kernel" K(x) (dose to detector signal). K(x) is calculated from FT[K(x)] = [1/sqrt(2Ï€)]FT[KM(x)]/FT[KD(x)], where the magnitude of kV(x) can be thereby calculated for arbitrary photon beam profiles and the area-normalized K(x).

In order to take into account for the dimensions of dosimetric detectors in narrow photon beams, the "volume effect correction factor" kV has been introduced into the fundamental equation of probe-type dosimetry, and the convolution method has proven to be a method for the derivation of its numerical values. For narrow photon beams, whose width is comparable to the secondary electron ranges, kV can reach very high values, but it can be shown that the signals of small diamond detectors are well representing the absorbed dose to water averaged over the detector volume.

Contact Email: