A comparison of the dosimetric properties of The Electronic Portal Imaging Devices (EPIDs) LC250 and aS500

Abstract

Aim

The aim of this paper was to compare the dosimetric properties of two different electronic portal imaging systems (EPID) used in the verification of doses.

Materials/Methods

The Portal Vision (PV) LC250 and aS500 machines were used. The Portal Vision device is liquid-filled while the second machine is based on amorphous silicon. Stability and the reproducibility of signals were investigated. The relationship between the readings from EPID devices and the exit dose rate was established. Dependencies between the responses of the EPID signal and the field size, phantom thickness and source-detector distance were studied. The EPIDs measurements were compared with those from an ionization chamber in the slab phantom. The relationships were described using mathematical functions. All measurements made were based on a 6MV linear accelerator photon beam CLINAC 23EX (Varian).

Results

Both devices are characterized by good stability and reproducibility. The dosimetric characteristics of EPIDs are different.

Conclusions

The Portal Vision LC250 and the PV aS500 are attractive tools for dosimetry purposes. In the case of the liquid-filled PV, deformation of the beam image profile by setting-up of the gantry at angles other than 0 or 180 degree was observed.