Program Information
Automatic Alignment-Free Iso-Center Validation Via Radioluminescent Phantoms and Optical Imaging
L Skinner*, C Jenkins, L Xing , Stanford Univ School of Medicine, Stanford, CA
Presentations
SU-H3-GePD-T-3 (Sunday, July 30, 2017) 4:00 PM - 4:30 PM Room: Therapy ePoster Lounge
Purpose: Isocenter validation of radiotherapy linear accelerators (LINACS) is of paramount importance among quality assurance (QA) procedures. Radiosurgery and hypofractionation have further increased the need to ensure accurate treatment delivery. For these techniques, it is vital that even sub-millimeter variations in dose delivery are accurately measured. To this end, we have developed a novel self-calibrating system that utilizes a radioluminescent phantom to perform automated iso-center verification. This automatic system reduces both the time and effort required to perform the tests, as well as improves measurement accuracy by eliminating dependence on operator setup.
Methods: The autonomous QA system consists of a cubic phantom, fabricated on a 3D printer, coated with a mixture of Gd2O2S:Tb and PDMS. This radioluminescent phantom is placed on the treatment couch near iso-center (+/- 5cm), and a digital camera is used to image 5x5 cm fields delivered from various gantry and collimator angles. Images are used to determine the entry and exit point of each beam relative to the phantom. Optical fiducials on the phantom enable automatic compensation for variations in phantom setup. Results taken from various phantom and camera positions are compared to evaluate self-calibration accuracy.
Results: The standard deviation for measurements made with a single phantom setup is approximately 0.1mm. Measurements made with multiple phantom setups have a standard deviation of approximately 0.2 mm with no significant change in average measurement value, indicating that the system is capable of compensating for any setup inaccuracy of the phantom. Total time for setup, measurement, analysis and clean-up is approximately 10 minutes.
Conclusion: The self-calibrating, automatic QA system successfully demonstrates the ability to autonomously perform iso-center verification of a clinical LINAC in approximately 10 minutes. The system also demonstrates an ability to produce accurate and consistent results in the presence of large perturbations in setup.
Funding Support, Disclosures, and Conflict of Interest: Funded by R01 grants: R01 CA176553 and R01 EB016777
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