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Dosimetric Data for Small Fields (Square and Stereotactic Cone) for Commissioning of 6MV FFF Beams in the RayStation Treatment Planning System

Y Lee*, Y Kim, University of Arizona, Tucson, AZ


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: There is a paucity of the literature on small field dosimetric data for commissioning of 6MV flattening filter free (FFF) beams in the RayStation treatment planning system (TPS). Therefore, this study presents dosimetric data (percent depth doses (PDDs), profiles and output factors) for small fields of =4cm × 4cm and stereotactic radiosurgery (SRS) cones for commissioning of 6MV FFF beams in the RayStation TPS.

Methods: PDDs for 5 square fields (0.6cm x 0.6cm, 1cm x 1cm, 2cm x 2cm, 3cm x 3cm and 4cm x 4cm) were measured on TrueBeam STx with 6MV FFF beams using the Sun Nuclear 3D water tank, Edge detector and Reference detector. Profiles were measured at dmax, 5cm, 10cm and 20cm and output factors at 10cm. For all measurements, SSD was set to 100cm. Measurements were repeated for 7 SRS cones (4mm, 5mm, 7.5mm, 10mm, 12.5mm, 15mm and 17.5mm in diameter) using the same setup and equipment except for profiles at 20cm. For output factors, the daisy-chain method was used and correction factors taken from the literature were applied for fields of =2cm x 2cm and all the cones.

Results: For fields of =4cm × 4cm, 5 PDDs and 20 cross-line profiles were acquired. For cones, 7 PDDs and 21 cross-line profiles were acquired. PDD parameters such as dmax, D10 (relative dose (%) at 10cm) and D20 (relative dose (%) at 20cm) decreased with decreasing field size or cone size. Output factors obtained for both cases also decreased with decrease in field size or cone size. The decreases were more drastic in fields of =1cm x 1cm and cones of =5mm.

Conclusion: The data presented in this study would be a good reference for the clinic which will commission 6 MV FFF beams in the RayStation TPS for SRS and/or SBRT treatment.

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Treatment Planning, Commissioning, Small Fields


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