IMRT verification with a camera-based electronic portal imaging system

Abstract

An evaluation of the capabilities of a commercially available camera-based electronic portal imaging system for intensity-modulated radiotherapy verification is presented. Two modifications to the system are demonstrated which use a novel method to tag each image acquired with the delivered dose measured by the linac monitor chamber and reduce optical cross-talk in the imager. A detailed performance assessment is presented, including measurements of the optical decay characteristics of the system. The overall geometric accuracy of the system is determined to be +/-2.0 mm, with a dosimetric accuracy of +/-1.25 MU. Finally a clinical breast IMRT treatment, delivered by dynamic multileaf collimation, is successfully verified both by tracking the position of each leaf during beam delivery and recording the integrated intensity observed over the entire beam.

Simple Proposal for Dosimetry with an Elekta iViewGTTM Electronic Portal Imaging Device (EPID) Using Commercial Software Modules

“…Applications of portal dosimetry have been reported for the type of EPIDs based on a liquid-filled ionization chamber matrix [2,5,6,26,27] and the CCD camera-based EPIDs [16]. More recently, amorphous silicon (a-Si)-based EPIDs have been developed with excellent image quality [17] and requirements for dosimetric purposes [3,7,8,10,12,13,15].…”

On Radiotherapy Dose Verification With a Flat-Panel Imager

“…33,84 Other studies converted EPID images to dose images at the detector plane, in some cases behind a phantom. 24,42,48,60,73,87,95,129 Alternatively, EPID images were used to reconstruct the dose in a plane within the patient or phantom 2,11,45,65,94,115,131 . Of these studies, some have explored the possibility of using an a-Si EPID for dose verification of IMRT fields.…”

“…Of these studies, some have explored the possibility of using an a-Si EPID for dose verification of IMRT fields. 2,24,42,94,115,131 A backprojection algorithm (described in chapter 5 of this thesis) forms the basis of the EPID dosimetry program in our department. The transmission signal measured at the level of the EPID is used to reconstruct the dose either inside a phantom or the patient.…”

“…EPIDs have been shown to be useful for intensity modulated radiotherapy (IMRT) pretreatment dosimetry. 24,78,94,95,131,132,139 Converting an EPID image to a dose distribution pre-treatment (with or without a phantom) allows for verification of the dose calculation and plan deliverability. The drawback is, however, that errors occurring at the time of treatment would be missed and it is not clear a priori how errors detected pre-treatment would translate to errors within a patient.…”

Sensitivity of an Elekta iView GT a-Si EPID model to delivery errors for pre-treatment verification of IMRT fields

“…However, these devices have limitations, film, although high resolution does not give real-time readout and the two dimensional arrays have poor spatial resolution. Amorphous-silicon flat panel electronic portal imaging devices (EPIDs) combine a high spatial resolution and large detection area and have been shown to be suitable for pre-treatment verification of IMRT fields [1][2][3][4][5][6]. Despite a number of commercial solutions becoming available their use has historically been mainly limited to research active departments with the resources available to develop in-house solutions [7][8][9][10].…”