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Dosimetric Comparison of SBRT VMAT Treatment Plans Generated for 6 MV, 6 MV FFF, and 10 MV FFF Photon Beams
D Wilson*, B Wang , N Dunlap , Univ Louisville, Louisville, KY
Presentations
SU-E-T-308 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose:To assess differences in treatment plan quality between VMAT stereotactic body plans generated using the 6 MV, 6 MV FFF, and 10 MV FFF modalities available in our clinic. Plans for lung, spine, and other sites were compared to see if there is any advantage of one modality over the other.
Methods:Treatment plans done for actual SBRT patients were selected. Groups of ten lung plans, five spine plans, and five plans from other sites were selected. New treatment plans were generated for each plan using the Varian Eclipse AAA algorithm. The constraints were kept the same as used in the actual plans, but the same version of software was used to generate plans for the three modalities. In addition, because there are natural variations in plans re-done with the same dose constraints, one of the lung plans was repeated ten times to assess those differences. Volumes of the 100%, 90%, 50%, 20% and 10% isodose surfaces were compared. Maximum dose two centimeters from the PTV were compared, as well as the volume of the 105% isodose surface outside of the PTV. In addition, the 20 Gray lung volume was compared for the lung plans. The values of these parameters were divided by the values for the 6 MV plans for comparison. Average and standard deviations were obtained for quantities in each group. The Student t test was done to determine if differences were seen at the 95% confidence level.
Results:Comparison of the treatment plans showed no significant differences when assessing these volumes and doses. There were not any trends seen when comparing modalities as a function of PTV volume either.
Conclusion:There is no obvious dosimetric advantage in selection of one modality over another for these types of SBRT plans.
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