Comparison of IQM and Varian Portal Dosimetry for pre-treatment VMAT QA

Vanderbilt University Medical Center (VUMC) is one of the leading Radiation Oncology Centers in the US and a Varian reference site.
Medical Physicists at VUMC compared IQM with Varian Portal Dosimetry for pre-treatment QA of various VMAT treatment techniques and published their results in the Journal of Applied Clinical Medical Physics (JACMP) Vol. 22 of March 2021.

To make a long story short:

IQM provides superior results in every aspect of their comparison with Varian Portal Dosimetry

Here are some of the findings of this study:

1. The IQM Detector demonstrates higher reproducibility and signal stability than the EPID.
2. IQM shows superior error detection capabilities than the EPID.
   This was particularly true when results were compared to those of Portal Dosimetry γ analysis in which most errors were not detected unless the strictest criteria of 1%/1 mm were applied. However, applying a 1%/1mm criteria to the Portal Dosimetry γ analysis gives a high rate of false positive errors.
3. When comparing the two sets of measurements with DVH data from the TPS, IQM shows a visibly stronger correlation to dose than EPID.
4. Loss of detector panel calibration can lead to false positives in evaluation of QA results and require periodic recalibration of the EPID panel. These limitations directly affect EPID measurement reproducibility and signal stability, and noticeably impact on VMAT QA results. These limitations do not apply to the IQM system.

While VUMC assessed pre-treatment QA, this high quality of verification is easily attainable for every treatment fraction. IQM’s completely automated integration into the clinical workflow provides unrivaled verification accuracy without any user interaction. For pre-treatment or fraction QA.