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Characterization of Efficiency and Plan Quality for the FFF Beams On Various Anatomical Sites

P Rassiah-Szegedi

P Rassiah-Szegedi*, M Szegedi , V Sarkar , H Zhao , Y Huang , L Huang , B Salter , University of Utah Huntsman Cancer Institute, Salt Lake City, UT


SU-E-T-166 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

To characterize efficiency and plan quality for the FFF beams for various sites.

5 brain, Head and Neck, prostate, lung and liver cancer patients IMRT plans (25 total) were generated on either Prowess 4.6 or Eclipse 13.5 using the same dose constraints for each treatment site. Step and shoot with static gantry IMRT was used for treatment delivery.
PTV coverage, critical structure doses, MUs, number of segments and beam on times were compared.

The average PTV size was 29.0, 34.9, 89.2, 257.6, 289.2 cm3 for liver, lung, prostate, head and neck and brain respectively.
All plans were normalized such that 95% of the PTV volume would receive at least 95% of prescribed dose. All doses to the critical structures for both the FFF and flat beam met the targeted dose constraints.
For plans with field sizes < 10 cm, the number of segments and MUs required to achieve the same plan quality were similar. For these small field sizes with large dose per fraction, an increase in efficiency up to 58.8% is seen.
Plans with field sizes > 10 cm, required 10% – 20% more segments and MUs for the FFF beam to achieve the same plan quality as the flat beam. Despite this, for fraction sizes less than 2.5 Gy the FFF beam is still approximately 13.9% more efficient in terms of delivery time.

For the various treatment sites studied here, plans generated with the FFF beam were dosimetrically similar to those generated with a flattened beam. Despite the greater number of MUs and segments required to achieve the same plan quality as the flat beam for some plans, the FFF beam is still more efficient compared to the flat beam.

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