Remote dosimetric auditing for intensity modulated radiotherapy: A pilot study

Abstract

Background and Purpose: Electronic portal imaging devices (EPIDs) can be used to reconstruct dose inside a virtual phantom. This work aims to study the feasibility of using this method for remote dosimetry auditing of clinical trials. Materials and Methods: Six centres participated in an intensity modulated radiotherapy (IMRT) pilot study of this new audit approach. Each centre produced a head and neck (HN) and post-prostatectomy (PP) trial plan and transferred the plans to virtual phantoms to calculate a reference dose distribution. They acquired in-air images of the treatment fields along with calibration images using their EPID. These data were sent to the central site where the images were converted to 2D field-byfield doses in a flat virtual water phantom and to 3D combined field doses in a cylindrical virtual phantom for comparison with corresponding reference dose distributions. Additional test images were used to assess the accuracy of the method when using different EPIDs. Results: Field-by-field 2D analysis yielded mean gamma pass-rates of 99.6% ( ± 0.3%) and 99.6% ( ± 0.6%) for HN and PP plans respectively (3%/3 mm, doses greater than 10% global max). 3D combined field analysis gave mean pass-rates of 97.9% ( ± 2.6%) and 97.9% ( ± 1.8%) for the HN and PP plans. Dosimetry tests revealed some field size limitations of the EPIDs. Conclusions: The remote auditing methodology using EPIDs is feasible and potentially an inexpensive method.