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Dosimetric and Mechanical Validation of a Varian Halcyon Linear Accelerator

T Jarema*, T Aland , A Walsh , R Murry , Radiation Oncology Centres, Toowoomba, QLD


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: This work was performed to independently validate the mechanical and dosimetric properties of the Varian Halcyon linear accelerator (Halcyon), a radiotherapy treatment device that comes pre-configured in the Eclipse treatment planning system. The Halcyon does not have a light field, optical distance indicator, or accessory mount, instead utilising a Varian developed tool called ‘machine calibration’ to calibrate and initialise all mechanical axes.

Methods: Machine calibration was performed to initially calibrate all axes of the system. Additional independent testing was performed to validate these calibrations and commission the system for clinical use.Mechanical validation utilised water equivalent slabs (with thimble ionisation chambers) and SNC Winston Lutz phantom to initially verify the positional accuracy of the fixed inline megavoltage electronic portal imaging device (EPID). The EPID was then used as the primary tool for validating all other axes, in lieu of using more traditional methods. For dosimetric validation, a PTW BEAMSCAN water phantom was utilised using a unique in-house developed methodology for positioning the BEAMSCAN inside the Halcyon bore. Dosimetric results were compared to the pre-configured Eclipse Anisotropic Analytical Algorithm (AAA) model.

Results: Mechanical test results were compared to ‘system calibration’. All mechanical results agreed with the machine calibration results, with differences being within 1mm±0.5mm or 1°±0.5°.Measured dosimetric data was compared against the treatment planning system data. PDDs and profiles for various field sizes, as well as point dose results for both on and off axis fields agreed to within 2mm or 2% of the beam model.

Conclusion: The pre-configured and calibrated Varian Halcyon linear accelerator was mechanically and dosimetrically validated using independent methodologies.All dosimetric results were found to be within 2% or 2mm of the pre-configured Eclipse AAA algorithm, and all mechanical results were found to be within 1mm or 1° of the in-built system calibration.


Validation, Dosimetry, Linear Accelerator


Not Applicable / None Entered.

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