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Flattened Photon Beams, An Obsolete Feature in Modern LINACS

J Wan*, J Bogue , D Shvydka , S Tanny , E Parsai , University of Toledo Medical Center, Toledo, OH


(Monday, 7/30/2018) 9:30 AM - 10:00 AM

Room: Exhibit Hall | Forum 7

Purpose: Flattening Filter-Free (FFF) beams have several advantages over traditional flattened beams including dramatically increased dose rate, reduced head leakage, simplified Linac design, and a lack of differential beam hardening. However, traditional beams are overwhelmingly used to deliver teletherapy and 3D conformal therapy because of their ‘uniform’ beam qualities across a treatment field. We demonstrate that utilizing sliding window IMRT optimized plans of similar or better quality are achievable with FFF beams thus obviating the need for flattening filters.

Methods: A two stage investigation was carried out. First, flat dose profiles were delivered to a water phantom with 6MV flat beam using 10x10 to 30x30cm2 open-fields. Using 0.1cm thick square plane structure for the IMRT optimization process same set of profiles was re-created with 6FFF beams. Next, the study was expanded to clinical treatments, evaluating 5 head & neck and 5 lung/mediastinum plans. Original plans completed with 6MV flattened beams were approved by radiation oncologists. New plans were accomplished with 6FFF beams to achieve the same PTV coverages and compare doses to OARs.

Results: The overall uniformity of line dose profiles across the CAX at 10cm depth showed 1-2% superiority of optimized FFF beams. Most of mean doses and volumes of the OARs receiving between 5% and 30% of the prescription dose were reduced with FFF plans, with only slightly increased maximum doses.

Conclusion: Our results successfully demonstrated how to deliver a conventional flat beam using FFF photon beam. Field uniformity was improved with the use of our sliding window technique. Clinical treatment plans demonstrated improved dosimetry using FFF beams because of the improved field uniformity. Beam-on times were reduced by X% using FFF compared to treatment with flattened beams.


Flattening Filters, X Rays, Treatment Planning


TH- External beam- photons: Development (new technology and techniques)

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