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Introduction of a Generalizable Method of Couch Attenuation Characterization and Its Application to Couch Commissioning and the Development of a RayStation EMC Compatible Couch Model

C Collins*, Y Yang, U Langner, M Schwer, Brown University Warren Alpert Medical School/Rhode Island Hospital, Providence, RI


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

Room: AAPM ePoster Library

Purpose: work designs and models a generalizable method of couch attenuation characterization. The method is applied to related clinical issues: development of an eMC-compatible couch model using preexisting RayStation density library materials, commissioning verification, and assessment of whether patients should be re-planned following couch replacement. The eMC calculation with a couch model composed of a user-defined density is not permitted in RayStation8A. Therefore, the development of a model that fits measurements to pre-existing library materials is imperative.

Methods: Unlike TG-273 that recommends a cylindrical phantom, this method uses 20.6cm of 30x30cm2 Solid Water with a cylindrical ionization chamber positioned at 10.3cm depth, 100cm-SAD. Measurements were collected at 6MV and 10MV with 4x4cm2 and 15x15cm2 fields. Forty dose measurements were collected at anterior and posterior opposed gantry angle pairs with 5 degrees of separation, and percentage attenuation for each pair was calculated. A Solid Water CT-scan was imported into RayStation to compare measurement values with RayStation modeled attenuation through a user-defined density couch model of the same dimensions as the PerfectPitch/IGRT couch. A new couch model composed of RayStation library materials was developed to fit this data.

Results: values for the couches were verified across two institutions and three couches (all corresponding values were within 1.5%). An eMC compatible RayStation couch model was developed using density library materials LN10 and PMI Foam. The percent difference in attenuation between this model and measurements was within 0.75% and presented a 0.1-0.8% dosimetric improvement over current user-defined density (non-eMC-compatible) models.

Conclusion: The method of couch attenuation characterization was verified. It was decided that upon couch commissioning, patients currently on treatment do not need to be re-planned when switching from a BrainLAB couch to the Varian PerfectPitch/IGRT. A new eMC-compatible couch model was developed and found to present both a dosimetric and workflow efficiency improvement.

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TH- External Beam- Photons: Development (new technology and techniques)

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