What is a “Beam Output Audit”

A BOA is an independent external dosimetry audit providing verification of the dose delivered by a radiotherapy beam, typically performed under reference conditions (e.g. 10 × 10 cm² field size, 5 cm or 10 cm depth in water). The audit report must be submitted to the EORTC RTQA team to confirm accurate dose delivery for trial patients.

Key references:
Bentzen et al Eur J Cancer 36:615-620, 2000. (PubMed)
Pettersen et al, Radiother Oncol 86:195-99, 2008 (PubMed)

Why is a BOA required?

European regulations require radiotherapy equipment to be calibrated at acceptance and following major repair. In addition, local quality assurance programmes include routine output checks (daily, weekly and/or monthly) to ensure calibration stability, with corrective actions taken when tolerance levels are exceeded.

However, even when local QA systems are followed rigorously, absolute dose delivery may still differ between centres. To ensure dose uniformity across centres participating in international clinical trials, local measurements must therefore be linked to national standards, which are themselves inter-compared internationally. External BOAs, such as TLD inter-comparisons, provide an independent means of detecting systematic calibration errors that may not be identified through local QA alone.

Criteria for a valid BOA

  • Audit date must be within the last 3 years.
  • The auditor’s primary standard must have traceability to a national/international primary standard.
  • Dose accuracy must be assessed under reference condition
  • The audit must be independent of the centre and include a clear irradiation date and official signature.
  • At least the photon beam energy(ies) and mode(s) (FF vs FFF) used for the intended trial(s) must be audited per set of matched treatment units.
  • For protons, a dose measurement for a relevant subset of energies used for the intended trial(s) must be audited
  • For electrons, a dose measurement of the intended beam energy(ies) used for the intended trial(s) must be audited per set of matched treatment units
  • Agreement should preferably be within 3%; 3–5% is acceptable.

Recognised Beam Output Audit Providers

Some countries may have a national or regional metrology-based dosimetry audit programme; where such a programme is not available, an audit may be arranged with an independent external organisation.

If your Radiation Oncology Department needs to set up an audit, the following audit providers are suggested:

However, it is not mandatory to obtain an audit from one of these providers: if a document satisfies all of the criteria detailed at “Criteria for a valid BOA” it will be evaluated and could be accepted even if the auditing organisation is, for example, the physics department of a neighbouring hospital.