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Clinical Testing and Dosimetric Characterization of the Elekta CalCo, Calypso Compatibility Pad

r brody*, oregon health and science university, Portland, OR


(Wednesday, 8/1/2018) 10:00 AM - 10:30 AM

Room: Exhibit Hall | Forum 6

Purpose: The Calypso (CalCo) pad was developed by Elekta (Elekta AB, Stockholm, Sweden) to enable the use of their carbon couchtops with the Calypso (Varian Ltd., Palo Alto, CA) radiofrequency beacon tracking system. The CalCo pad allows users with the iGuide 6-degree couch to also use the Calypso system. The CalCo pad contains dense foam and a proprietary, “ferrite� layer to counter RF interference from the carbon couchtop. This novel support structure has been commissioned for use through dosimetric characterization and end-to-end workflow verification tests.

Methods: Dosimetric characterization was performed by measuring the pad’s attenuation properties using an Elekta VersaHD linear accelerator. Pad contributed attenuation was measured in solid water with an Advanced Markus chamber (PTW Type 34045). Percent-depth-dose profiles were obtained using GAFCHROMIC EBT3 film to assess the pad’s effect on the build-up region. Relative attenuation measurements were used to develop a pad model for the Monaco (v.5.11.02 , Elekta) treatment planning system. Calypso daily QA was performed with the pad in place on the ELEKTA carbon couchtop. Clinical workflow, end-to-end tests for a Calypso prostate treatment were performed with the pelvis portion of the Alderson RANDO phantom having three Calypso beacons embedded between phantom slices.

Results: The introduction of the CalCo pad to the normally incident beamline contributed an additional 3.2%, 2.1%, 2.1%, 3.1%, and 2.7% attenuation for 6MV, 10MV, 18MV, 6FFF MV, and 10FFF MV energies, respectively. In Monaco, the ferrite layer and foam structures were assigned relative electron densities (RED) of 1.80 and 0.02, respectively. These RED values gave TPS calculated attenuation values within 1% of those previously measured.

Conclusion: With appropriate characterization and end-to-end testing, in our experience, the CalCo pad can be used with an Elekta carbon couchtop and the Varian Calypso system without detriment to clinical, prostate workflow.


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