WE-G-BRB-08: TG-51 Calibration of First Commercial MRI-Guided IMRT System in the Presence of 0.35 Tesla Magnetic Field

Medical Physics
S GodduSasa Mutic

Abstract

The first real-time-MRI-guided radiotherapy system has been installed in a clinic and it is being evaluated. Presence of magnetic field (MF) during radiation output calibration may have implications on ionization measurements and there is a possibility that standard calibration protocols may not be suitable for dose measurements for such devices. In this study, we evaluated whether a standard calibration protocol (AAPM- TG-51) is appropriate for absolute dose measurement in presence of MF. Treatment delivery of the ViewRay (VR) system is via three 15,000Ci Cobalt-60 heads positioned 120-degrees apart and all calibration measurements were done in the presence of 0.35T MF. Two ADCL- calibrated ionization-chambers (Exradin A12, A16) were used for TG-51 calibration. Chambers were positioned at 5-cm depth, (SSD=105cm: VR's isocenter), and the MLC leaves were shaped to a 10.5cm × 10.5 cm field size. Percent-depth-dose (PDD) measurements were performed for 5 and 10 cm depths. Individual output of each head was measured using the AAPM- TG51 protocol. Calibration accuracy for each head was subsequently verified by Radiological Physics Center (RPC) TLD measurements. Measured ion-recombination (Pion) and polarity (Ppol) correction factors...Continue Reading

Citations

Mar 13, 2019·Journal of Applied Clinical Medical Physics·Fang LiuAlan B McMillan
Aug 29, 2019·Journal of Applied Clinical Medical Physics·Jeongmin YoonJong Min Park
Nov 8, 2017·Abdominal Radiology·Eugene J KoayJoseph M Herman
Dec 25, 2015·Journal of Applied Clinical Medical Physics·Daniel L SaenzBhudatt R Paliwal
Jun 15, 2017·Japanese Journal of Radiology·Ilamurugu ArivarasanVelayudham Ramasubramanian

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