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SU‐E‐T‐136: Dosimetric Robustness of a Magnetic Resonance Imaging Guided Radiation Therapy (MR‐IGRT) System
Author(s) -
Rodriguez V,
Green O,
Wooten H,
Kashani R,
Mutic S,
Dempsey J,
Li H
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4888466
Subject(s) - image guided radiation therapy , ionization chamber , nuclear medicine , proton therapy , quality assurance , radiation treatment planning , radiation therapy , dosimetry , medicine , medical physics , physics , radiology , ionization , ion , external quality assessment , pathology , quantum mechanics
Purpose: To test the radiation delivery robustness of the first MR‐IGRT system using a commercial cylindrical diode array detector (ArcCHECK) and an ionization thimble chamber (Exradin A18). Methods: The MR‐IGRT system is composed of three evenly spaced Co‐60 sources on a rotating gantry located between two magnet halves. The collimator for each source consists of 30 doubly‐focused leaf pairs that allow the system to deliver both conformal and intensity modulated (IMRT) treatment plans. The system's delivery robustness was tested over a span of 6 months from September 2013 through February 2014. This was achieved by repeatedly delivering 10 patient plans. These plans consisted of 2 conformal prostates, 2 IMRT prostates, 2 IMRT head and neck, 2 IMRT breast, 1 IMRT pancreas, and 1 IMRT bladder. The plans were generated with the system's treatment planning software. Once the plans were generated, quality assurance plans were created on a digital ArcCHECK dataset. The ArcCHECK used for testing was specially designed to be MR‐compatible by moving the power supply outside of the magnetic field. The A18 ionization chamber was placed in a custom plastic plug insert in the center of the ArcCHECK. Gamma analysis was used with the ArcCHECK for relative dose evaluating both 3%/3mm and 2%/2mm. Absolute point dose was compared between ion chamber measurement and treatment plan. Results: The ArcCHECK passing rate remained constant over the 6 month period. The average passing rate for 3%/3mm and 2%/2mm analysis was 98.6% ± 0.7 and 88.8% ± 2.9, respectively. The ion chamber measurements showed little variation with an average percent difference between planned dose verses measured dose of 0.9% ± 0.7. Conclusion: Minimal differences were noted in the delivery of the 10 patient plans. Over a period that included acceptance testing, commissioning, and clinical deliveries, the MR‐IGRT system remained consistent in radiation delivery.