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Error in Vendor Provided Calibration for Pre-Clinical Orthovoltage Irradiator Identified Through Independent Output Check

D Carlton1*, T Howard2, Q Chen1, (1) University of Kentuky, Lexington, KY, (2) Texas Oncology, Dallas, TX


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

Room: AAPM ePoster Library

Purpose: Accurate radiation dosimetry in radiobiological experiments is crucial to the pre-clinical research for advancement of cancer treatment. Vendors of cell irradiators often perform calibration for end-user. However, details on the calibration procedure is often missing, which brings questions the calibration accuracy. In this study, we presented our independent calibration check of a recently purchased XRAD-225 orthovoltage irradiator, and our investigation on the major discrepancy observed.
Methods: Radiochromic film (EBT-3) was used as dosimeter for the independent output check. The film was calibrated at MV energy. An energy correction factor published in literature was used to convert the film calibration to the kV beam quality of the XRAD-225 irradiator. Surface dose under full backscatter condition was measured with film. An A1SL ion chamber calibrated at kV energy was used to further validate the machine calibration. A thin tape is used to support the ion chamber for in-air measurement following TG61. Based on information provided by vendor regarding their calibration setup, Monte Carlo simulation was performed to investigate the impact of their non-standard setup.
Results: Independent output check with film showed that the machine output is 6% less than expected. Ion chamber in-air measurement at corrected SSD shows the machine is mis-calibrated by 4-5%. Vendor’s incorrect setup was simulated with Monte Carlo and the results agreed with our measurement. The impact of the board would increase the ion chamber reading by 9.3-11.2%. It is also discovered that the vendor did not perform temperature and pressure correction for their ion chamber.
Conclusion: A major vendor of preclinical kV irradiator has been consistently mis-calibrate their machine by 4-5% or more. It is important to have a physicist performing independent output checks on preclinical kV irradiator. Radiochromic film has been shown to be a reasonable choice for this purpose.


Calibration, Radiochromic Film, Low Energy X-rays


TH- Small Animal RT: Experimental Dosimetry

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