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Session: Therapy General ePoster Viewing [Return to Session]

Investigation of the Dosimetric Effects of An SBRT Positioning System

D Baldassari*, C Esquivel, K Andrews, L Patton, Texas Oncology San Antonio, San Antonio, TX


PO-GePV-T-290 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: Investigate the potential dosimetric impact of the Bionix SBRT system on the patient.

Methods: The Bionix RT-4500 Omni-V SBRT system was investigated for the potential dosimetric influence on patients. Structures not unaccounted for during planning may result in inaccurate skin dose and dose coverage. Skin dose measurements acquired using Varian 21iX and 6MV beam. The Edge diode-detector was placed at 100cm SAD, adjacent to each component, for varying field sizes (10x10, 6x6, 4x4, 2x2cm².) The components included the compression belt (with and without insert), chest compression plate (thickest and thinnest part) of the Turner Arch, and the body support vacuum cushion (2, 5, 10cm thicknesses). For attenuation effects, the diode detector was place at 100cm SAD and 10cm depth in solid water (90cm SSD) for the same field sizes. The SecureFit Bar (center and lock tab), side-rail belt-attachment, Turner Arch, and the base of the SBRT system were placed on top of the phantom.

Results: With the Eclipse TPS, anything outside the body contour is not considered dosimetrically. Components of the immobilization system must be scrutinized and appropriately considered. Oversight of a device can result in increased surface dose or reduced coverage of the target due to attenuation. Skin dose increases as the field size increases. For attenuation effects, there is a slight decrease of the radiation dose as the field size decreases.

Conclusion: Measurements traversing various components of the Bionix SBRT system have been reported for user reference within the radiation oncology community. Apart from the T-Vac Cushion on which the patient lies, most components can be knowingly avoided within the treatment planning process. While minimal attenuation of the beam through parts of the device may be observed, unintended skin dose may be significant.



    Not Applicable / None Entered.


    TH- External Beam- Photons: General (most aspects)

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