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Burst-Mode Modulated Arc Therapy with Flattening-Filter-Free Beams Versus Flattening-Filtered Beams

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K Kainz

K Kainz*, C Lawton , X Li , Medical College of Wisconsin, Milwaukee, WI


SU-E-T-153 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose:To compare the dosimetry and delivery of burst-mode modulated arc radiotherapy using flattening-filter-free (FFF) and flattening-filtered (FF) beams.

Methods:Burst-mode modulated arc therapy (mARC, Siemens) plans were generated for six prostate cases with FFF and FF beam models, using the Elekta Monaco v. 5.00 planning system. One 360-degree arc was used for five cases, and for one case two 360-degree coplanar arcs were used. The maximum number of optimization points (OPs) per arc was set to 91, and OPs with less than 4 MU were disregarded. All plans were delivered on the Siemens Artiste linear accelerator with 6MV FF (300 MU/min) and comparable-energy FFF (2000 MU/min, labeled as 7UF) beams.

Results:For all cases studied, the plans with FFF beams exhibited DVHs for the PTV, rectum, and bladder that were nearly identical to those for the plans with FF beams. The FFF plan yielded reduced dose to the right femoral head for 5 cases, and lower mean dose to the left femoral head for 4 cases. For all but the two-arc case, the FFF and FF plans resulted in an identical number of segments. The total number of MUs was slightly lower for the FF plans for five cases. The total delivery time per fraction was substantially lower for the FFF plans, ranging from 25 to 50 percent among all cases, as compared to the FF plans.

Conclusion:For mARC plans, FFF and FF beams provided comparable PTV coverage and rectum and bladder sparing. For the femoral heads, the mean dose was slightly lower in most cases when using the FFF beam. Although the flat beam plans typically required slightly fewer MUs, FFF beams required substantially less time to deliver a plan of similar quality.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by Siemens Medical Solutions and the MCW Cancer Center Fotsch Foundation.

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