The use of electronic portal imaging devices (EPIDs) is a promising method for the dosimetric verification of external beam, megavoltage radiation therapy-both pretreatment and in vivo. In this study, a previously developed EPID back-projection algorithm was modified for IMRT techniques and applied to an amorphous silicon EPID. By using this back-projection algorithm, two-dimensional dose distr...

When using an electronic portal imaging device (EPID) for dosimetric verifications, the calibration of the sensitive area is of paramount importance. Two calibration methods are generally adopted: one, empirical, based on an external reference dosimeter or on multiple narrow beam irradiations, and one based on the EPID response simulation. In this paper we present an alternative approach based ...

The purpose of this study was to investigate the dose-response characteristics, including ghosting effects, of an amorphous silicon-based electronic portal imaging device (a-Si EPID) under clinical conditions. EPID measurements were performed using one prototype and two commercial a-Si detectors on two linear accelerators: one with 4 and 6 MV and the other with 8 and 18 MV x-ray beams. First, t...

Mandatory in several countries, in vivo dosimetry has been recognized as one of the next milestones in radiation oncology. Our department has implemented clinically an EPID based in vivo dosimetry system, EPIgray, by DOSISOFT S.A., since 2006. An analysis of the measurements per linac and energy over a two-year period was performed, which included a more detailed examination per technique and t...

In this study, we use the quadratic calibration method (QCM), in which an EPID image is converted into a matrix of equivalent path lengths (EPLs) and, therefore, exit doses, so as to model doses in conformal and enhanced dynamic wedge (EDW) fields. The QCM involves acquiring series of EPID images at a reference field size for different thicknesses of homogeneous solid water blocks. From these, ...

Patient-specific quality assurance for intensity-modulated radiation therapy (IMRT) dose verification is essential. The aim of this study is to provide a new method based on the relative error distribution by comparing the fluence map from the treatment planning system (TPS) and the incident fluence deconvolved from the electronic portal imaging device (EPID) images. This method is validated fo...

AIM The aim of the study was to estimate the dose at the reference point applying an aSi-EPID device in the course of patient treatment. MATERIALS AND METHODS The method assumes direct proportionality between EPID signal and dose delivered to the patient reference point during the treatment session. The procedure consists of treatment plan calculation for the actual patient in the arc techniq...

The aim of this study was to develop and apply an evaluation method for assessing the accuracy a novel 3D EPID back-projection algorithm in vivo dosimetry. Dosimetry Check (DC) 5.8 evaluated. A slab phantom homogeneously filled, or with air bone inserts, used fluence reconstruction different squared fields. VMAT plans anatomical sites were delivered on anthropomorphic phantom. Dose distribution...

Using an EPID for patient specific IMRT QA is an efficient way to verify patient plans prior to the treatment. Our centres’ current EPID dosimetry method is based on a water equivalent depth approach, where EPID images of each IMRT field are converted to dose images and compared to Treatment planning system calculated dose images using a commercial software tool. Two physicists across two sites...