Verification of setup errors in external beam radiation therapy using electronic portal imaging

Abstract

The objective of this study was to conduct an audit on QA aspects of treatment delivery by the verification of the treatment fields′ position on different days to document the efficiency of immobilization methods and reproducibility of treatment. A retrospective study was carried out on 60 patients, each 20 treated for head and neck, breast, and pelvic sites; and a total of 506 images obtained by electronic portal imaging device (EPID) were analyzed. The portal images acquired using the EPID systems attached to the Varian linear accelerators were superimposed on the reference images. The anatomy matching software (Varian portal Vision. 6.0) was used, and the displacements in two dimensions and rotation were noted for each treated field to study the patient setup errors. The percentages of mean deviations more than 3 mm in ‘lateral (X) and longitudinal (Y)’ directions were 17.5%, 11.25%, and 7.5% for breast, pelvis, and head and neck cases respectively. In all cases, the percentage of mean deviation with more than 5 mm error was 0.83%. The maximum average mean deviation in all the cases was 1.87. The average mean SD along X and Y directions in all the cases was less than 2.65. The results revealed that the ranges of setup errors are site specific and immobilization methods improve reproducibility. The observed variations were well within the limits. The study confirmed the accuracy and quality of treatments delivered to the patients.

Quality control test for electronic portal imaging device using QC-3 phantom with PIPSpro

“…Lutz 4,5 and the Las Vegas 6,7 phantoms has been reported to check the accuracy and the image quality for the qualitative visual QA checks of patient imaging. 8 Here in, we report a less subjective approach for automatic daily quality control tests to get better image quality for patient. In a study presently underway at our institute, an integrated EPID-based QA system is being developed, which aims to replace the conventional device-dependent methods for daily and monthly QA tasks.…”

How to improve x‐ray scattering techniques to quantify bone mineral density using spectroscopy

“…[20][21][22] The possible errors due to patient repositioning in the authors' scattering methods are likely comparable to those found in beam placement in image guided radiation therapy, of the order of a few millimeters, such as the 2-3 mm found in Ref. 23 for setup errors in external beam radiation therapy using electronic portal imaging. In cases in which the selected volume is sufficiently small and at a large distance from the cortical envelope, accurate positioning is not crucial since the authors' irradiated volume will still be inside the region that contains trabecular bone, even if positioning is imperfect.…”