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

Abstract

A Monte Carlo model of an Elekta iViewGT amorphous silicon electronic portal imaging device (a-Si EPID) has been validated for pre-treatment verification of clinical IMRT treatment plans. The simulations involved the use of the BEAMnrc and DOSXYZnrc Monte Carlo codes to predict the response of the iViewGT a-Si EPID model. The predicted EPID images were compared to the measured images obtained from the experiment. The measured EPID images were obtained by delivering a photon beam from an Elekta Synergy linac to the Elekta iViewGT a-Si EPID. The a-Si EPID was used with no additional build-up material. Frame averaged EPID images were acquired and processed using in-house software. The agreement between the predicted and measured images was analyzed using the gamma analysis technique with acceptance criteria of 3 %/3 mm. The results show that the predicted EPID images for four clinical IMRT treatment plans have a good agreement with the measured EPID signal. Three prostate IMRT plans were found to have an average gamma pass rate of more than 95.0 % and a spinal IMRT plan has the average gamma pass rate of 94.3 %. During the period of performing this work a routine MLC calibration was performed and one of the IMRT treatments re-measured with the EPID. A change in the gamma pass rate for one field was observed. This was the motivation for a series of experiments to investigate the sensitivity of the method by introducing delivery errors, MLC position and dosimetric overshoot, into the simulated EPID images. The method was found to be sensitive to 1 mm leaf position errors and 10 % overshoot errors.

Monte-Carlo techniques for radiotherapy applications II: equipment and source modelling, dose calculations and radiobiology

“…25 It is also worth noting that Monte-Carlo techniques have also been used widely for verifying treatment dosimetry through the use of Electronic Portal Imaging Detector (EPID)-based dosimetry. [26][27][28][29] The technique can offer an accurate calculation of the portal dose response of the detector for comparison to the measured portal dose.…”

Clinical Efficacy of an Electronic Portal Imaging Device versus a Physical Phantom Tool for Patient-Specific Quality Assurance

“…These Life 2022, 12,1923 2 of 12 detectors have the following advantages: stability for a short time, dose linearity, and simple dose calibration. However, they have an average volume effect, poor spatial resolution, and require phantom setup time [6,10,11].…”

“…An electronic portal imaging device (EPID) attached to the linear accelerator (LINAC) has a good resolution and a low volume-averaging effect; moreover, its setup is extremely simple [11][12][13]. Hence, the EPID can overcome the limitations of the array detector [14,15].…”

“…However, Elekta, which is another radiotherapy machine corporation, does not provide QA software. Hence, each institution has developed in-house software to use EPID [11,23].…”

The effect of respiratory motion on electronic portal imaging device dosimetry

“…Potential radiation delivery errors and intra‐ and inter‐fractional changes in the patient anatomy will be detrimental to the treatment outcome and are the reason in vivo treatment verification is highly desirable . EPID dosimetry is considered to be the favored modality for in vivo dosimetry going into the future and it has been shown to be effective for detecting the various types of errors encountered in the radiotherapy treatment …”