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A Clinical Review of the Dosimetric and Temporal Impact of Unflattened X-Ray Beams

J Bayouth

J Bayouth*, Y Huang, R Flynn, R Siochi, University Of Iowa, Iowa City, IA

MO-A-BRB-3 Monday 8:00:00 AM - 9:55:00 AM Room: Ballroom B

Since July of 2005, the University of Iowa has been using a conventional linear accelerator with the flattening filter removed. This presentation will focus on the factors affecting the dosimetric accuracy and total delivery time reduction found clinically of radiation therapy with an unflattened beam, focusing on standard fractionation IMRT of the head and neck, as well as gated and hypo-fractionated liver and lung cancer treatments. The dosimetric accuracy of the unflattened beam depends on the planning system beam model, which will be briefly reviewed. The technique used to adjust the beam quality to become equivalent with a beam utilizing the flattening filter, as well as the approach to define the field size for these beams will be described. Finally, the short-term beam stability (< 250 msec) for small MU IMRT and gated delivery will be characterized, along with the long-term stability from the last 5-years of clinical daily quality assurance records.

Learning Objectives:
1.Understand technique for matching beam quality of unflattened and flattened beams.
2.Understand definition of field size and beam characteristics during initial 200 msecs.
3.Review improved dosimetric accuracy and temporal advantages of unflattened beams in clinical use.

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