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Point/Counterpoint Live Debate: Modern Linacs Monitor Units Should Be Defined in Water at 10 Cm Depth Rather Than at DMAX

F Van den Heuvel1*, Q Wu2*, K Kielar3*, C Sandin4*, F Van den Heuvel5*, (1) University of Oxford, Oxford, ,(2) Duke University Medical Center, Durham, NC, (3) Varian Medical Systems, Palo Alto, CA, (4) Elekta Ltd, Crawley, WSX, (5) University of Oxford, Oxford, United Kingdom


(Wednesday, 7/17/2019) 2:45 PM - 3:45 PM

Room: Stars at Night Ballroom 4

Clinical linear accelerators need to be calibrated to ensure accurate and uniform treatment of cancer. There are widely adopted guidelines such as AAPM TG-51 and IAEA TRS-398, making linac calibrations consistent and accurate.
Modern linac photon beams are often isocentrically calibrated in water at fixed depths, and subsequently configured such that 1 monitor unit (MU) corresponds to 1 cGy at the depth of maximum dose, (dmax). While this is the classical approach, some physicists believe that there are simpler more consistent ways of configuration.
This debate tackles this question, with the help of two major vendors who plan to provide a historical perspective on the choice of calibration depth over the course of designing linacs and participate in the pros/cons in terms of safety and accuracy of patient treatment.

The final debate with a twist involves the authors from the Medical Physics article on this topic taking the opposite viewpoint from the original. This is followed by a panel debate, with audience participation.

Learning Objectives:
1) Differences between isocentric and fixed distance linac calibration.
2) Impact of Linac design on calibration procedures.
3) Procent Depth dose versus tissue to phantom ratio MU calculations.



Calibration, Dosimetry Protocols, Linear Accelerator


Education: Knowledge of principles and generalizations

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