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Commissioning of Brainlab Cones for 6xFFF and 10xFFF Beams On a Varian TrueBeam STx

D Wiant

D Wiant*, B Sintay, Cone Health Cancer Center, Greensboro, NC

SU-E-T-421 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To the best of our knowledge no data has been published on the use cones at 10xFFF and very little for 6xFFF. We report our experience commissioning and validating beam models for 4, 6, 7.5, 10, 12.5, and 15 mm cones on a Varian TrueBeam STx (Varian Medical Systems, Palo Alto, CA)).
Methods: Scatter factors, radial profiles, and percent depth dose curves were measured per Brainlab protocol using a Sun Nuclear Edge Detector diode (Sun Nuclear Corp., Melboune, FL). The resulting Brainlab iPlan (Brainlab AG, Germany) beam models were validated with measurements of absolute dose and profiles at depths of 5, 10, and 15 cm in a polystyrene phantom using EBT3 radiochromic film (Ashland Inc., Covington, KY). Absolute doses were evaluated by comparing the average of pixels in the planned dose that had values > 80% of the maximum dose to the average of the corresponding pixels in the film.
Results: The 6xFFF commissioning data was reviewed by Brainlab and found to be in good agreement with other user submitted data. Brainlab did not have a 10xFFF reference set at this time. The measured absolute dose agreed with planned dose to within 4.7% for all 6xFFF measurements (average difference of 2.1%) and within 4.9% for all 10xFFF measurements (average difference of 3.6%). Vertical and horizontal profiles through film planes gave full-width-at-half- maximum values that agreed with planned values to 0.4 mm for 6xFFF and to 0.2 mm for 10xFFF.
Conclusion: The calculated dose distributions showed acceptable geometric agreement with measured values. The measured absolute dose for both energies was consistently lower than planned dose, with the difference more noticeable for the 10xFFF energy. This effect may be explained by reported over responses of diodes at small fields and under responses of EBT film at small fields.

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