Background and Purpose:
Remote beam output audits, which independently measure an
institution’s machine calibration, are a common component of
independent radiotherapy peer review. This work reviews the results and
trends of these audit results across several organisations and geographical
regions.
Materials and Methods:
Beam output audit results from the Australian Clinical Dosimetry
Services, International Atomic Energy Agency, Imaging and Radiation Oncology
Core, and Radiation Dosimetry Services were evaluated from 2010 to the
present. The rate of audit results outside a +/−5% tolerance was
evaluated for photon and electron beams as a function of the year of
irradiation and nominal beam energy. Additionally, examples of confirmed
calibration errors were examined to provide guidance to clinical physicists
and auditing bodies.
Results:
Of the 210,167 audit results, 1323 (0.63%) were outside of tolerance.
There was a clear trend of improved audit performance for more recent dates,
and while all photon energies generally showed uniform rates of results out
of tolerance, low (6 MeV) and high (≥18 MeV) energy electron beams
showed significantly elevated rates. Twenty nine confirmed calibration
errors were explored and attributed to a range of issues, such as equipment
failures, errors in setup, and errors in performing the clinical reference
calibration. Forty-two percent of these confirmed errors were detected
during ongoing periodic monitoring, and not at the time of the first audit
of the machine.
Conclusions:
Remote beam output audits have identified, and continue to identify,
numerous and often substantial beam calibration errors.