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Session: Therapy General ePoster Viewing [Return to Session]

Linear Accelerator Head Leakage Testing Via XR-SP2 Radiochromic Film

Z Xia1, D Johnson2*, (1) Duke University, Durham, NC (2) The University of Kansas Medical Center, Kansas City, KS

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PO-GePV-T-330 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: Head leakage testing is one aspect of linear accelerator commissioning, assuring it is below regulatory limits and within vendor specifications. Traditional methods often illustrate the use of radiographic film to establish areas of interest about the gantry. As wet film processing is becoming increasingly uncommon, radiochromic film is a viable replacement.

Methods: A Varian TrueBeam was wrapped in Ashland XR-SP2 Gafchromic film. Film was cut to shape to reduce gaps in coverage and reduce film overlap. 1000 MU of 15MV photon beam was delivered through minimized MLCs and jaws. An ionization chamber was placed 1 meter from the subsequent observed surface “hot-spot” to measure the output relative to that at isocenter. The film demonstrating the maximum dose was subsequently digitized via flatbed scanner for additional analysis.

Results: The “hot spot” of the gantry head was identified on film and ion-chamber readings reveal leakage below those specified by the vendor. The maximum dose is determined to be on the top-center of the gantry, along the beamline, resulting from x-rays backscattering from the target. Results of red-channel film dosimetry via RIT software confirm the relative maximum about the head of the gantry.

Conclusion: Radiochromic film exhibits ease of use and versatility during head-leakage testing. As there is no need to remove the film for processing, results are effectively obtained in real-time, reducing the need to maintain film-jacket integrity and track physical positioning accuracy. The remaining film exhibiting reduced fogging levels may be additionally re-used for geometrical testing. As the ion-chamber results are the established standard, the use of radiochromic film to assure accurate positioning increases efficiency and reduces the likelihood of errors in measurement.

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