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Radiotherapy and diagnostic services

Radiotherapy dosimetry audits

Reference and end-to-end dosimetry audits for advanced radiotherapy

Expert audits and advice

At NPL, we offer a wide range of radiotherapy dosimetry audits, from reference dosimetry audits to end-to-end audit of advanced radiotherapy techniques, which are run in collaboration with the clinical trials QA group (RTTQA) and the UK SABR consortium, where appropriate.

Reference dosimetry audits

End-to-end audits

We also carry out Bespoke audits which you can tailor to your exact requirements

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Reference dosimetry audits

Photon and electron reference dosimetry audits

NPL carries out audits based on the UK IPEM codes of practice for therapy level MV photons, electrons and medium energy X-rays. The audit at a single beam quality consists of a beam quality check, output measurement and field instrument calibration. Local paperwork, data recording by the centre and procedures are not examined. Alanine is a solid-state dosimeter with a wide dose range (5-100kGy), low energy dependence and near tissue equivalence. The alanine pellets provided are traceable to the NPL UK primary standard, independently of the ion chamber chain.

  • An on-site audit in a single modality takes several hours, depending on how many qualities are examined.
  • Mutually convenient times are agreed, which can be outside normal working hours
  • Audit using the postal alanine service is available

Read more: Radiotherapy reference dose audit in the United Kingdom by NPL: 20 years of consistency and improvements.

Proton reference dosimetry audit

An on-site reference dosimetry audit based on the IAEA TRS-398 code of practice is available using ionisation chambers traceable to the NPL UK primary standard for photons. This consists of performing an independent dose check of the beam monitor calibration by performing measurements at a range of mono-energetic energies. Output measurements are also performed in at least three composite fields.

  • The audit takes two consecutive working daysreference_dosimetry.jpg
  • Mutually convenient times are agreed, which can be outside normal working hours.

NPL is finalising the commissioning of the world’s first primary standard proton calorimeter and the provision of a new calibration service following recommendations of the upcoming IPEM Code of Practice is under development.

Read more: Accelerating the uptake of proton beam therapy in the UK


MRI-Linac reference dosimetry audit 

An on-site reference dosimetry audit traceable to the NPL primary standard through alanine dosimetry, which is acting as a transfer standard and is corrected for the effect of the magnetic field (Billas et al, 2020). The audit consists of a beam quality check, output measurement and field instrument calibration.

  • An on-site audit takes one day
  • Mutually convenient times are agreed, which can be outside normal working hours
  • Audit using the postal alanine service is available

End-to-end dosimetry audits

As part of NPL’s work to support the UK’s digital journey, we have transitioned to online dosimetry audit services for SABR audits. This will automate and streamline the audit process while reducing complexity. Users will also be able to access their dosimetry audit reports via our online portal at any time.

SABR lung dosimetry audit

We provide a postal audit of lung cancer stereotactic ablative body radiotherapy (SABR), following the protocol developed as part of the UK SABR Consortium Lung national dosimetry audit. The audit is designed to assess the positional and dosimetric accuracy of a SABR lung treatment delivery. This is achieved with the use of alanine pellets and EBT3 GafChromic film dosimetry, placed in a CIRS Thorax phantom. The CIRS thorax phantom is a segmented phantom with regions of lung, spine and water equivalent density.

The alanine pellets are housed inside a Farmer shaped holder, which can be inserted into the CIRS thorax phantom. This means that you can perform a position check measurement using your own Farmer ionisation chamber prior to the audit measurements to ensure accurate setup.

  • The alanine and gafchromic film are mailed to your centre.
  • Each centre either uses their own CIRS thorax phantom or borrows one from a nearby centre, we are happy to help put you in touch with another centre if required.

Watch a video: Instructions for preparing the CIRS Thorax phantom for audit.

Read more: A national dosimetry audit for stereotactic ablative radiotherapy in lung.

Intracranial SRS end-to-end dosimetry audits

These are postal end-to-end dosimetry audits of intracranial stereotactic radiosurgery (SRS). The audits test the dosimetric accuracy of all aspects of the SRS treatment pathway, which are immobilisation, CT scanning, import of images into the Treatment Planning System (TPS), image fusion and treatment delivery. It is advised to include the multi-disciplinary team in the relevant steps in this audit.

The phantom used is a bespoke CIRS STEEV which has been adapted so that the alanine and Gafchromic EBT-XD film measurements can be performed simultaneously. The STEEV phantom is delivered to your centre pre-loaded with alanine and EBT-XD Gafchromic film, where you then send the phantom through your SRS treatment pathway from CT scanning through to delivery of the dose. Afterwards the phantom is returned to NPL where the alanine and Gafchromic films are unloaded and analysed. As part of this audit we also include a reference photon output measurement using alanine housed in a Farmer shaped insert, which can be inserted into your own solid water blocks. The audit can be offered for a single metastasis protocol and we are currently in the process of developing a protocol for multiple metastasis.


Single metastasis audit -This audit uses the same protocol as used during the NHS England national SRS dosimetry audit. Therefore, there is an added advantage that your results will be benchmarked against over 30 centres results.

Read more: Adaptation and validation of a commercial head phantom for cranial radiosurgery dosimetry end-to-end audit.

Multiple metastasis audit The audit will use a protocol based on three metastasis and will aim to assess the accuracy of the high dose as well as the fall-off region between metastasis.

Rotational IMRT audit

We can offer an on-site independent audit of rational intensity modulated radiotherapy (IMRT) techniques, VMAT and Tomotherapy. This audit makes use of either:

  • Octavia II Octagonal phantom (PTW) plus the 729 Detector Array and follows the protocol used during the 2013 National VMAT and Tomotherapy audit, or
  • Octavia 4D phantom (PTW) plus the 1500 Detector Array

Each centre creates a plan on the 3DTPS test developed by RTTQA, and measurements can also be performed using a centre’s own clinical plan.                          

Read more:

Proton beam therapy end-to-end dosimetry audit

NPL, in collaboration with MedAustron, provides an end-to-end dosimetry audit for scanned proton beams. It uses dedicated homogeneous and anthropomorphic head and pelvis phantoms, alanine and ionisation chambers (which are traceable to NPL) and radiochromic film.

Read more: Dosimetry Audit Service for Ion Beam Therapy

Bespoke audits  

We are also able to use our expertise to support bespoke audit needs. For example, we can provide alanine pellets for independent measurement of VMAT treatment plans. Centres are able to use their own phantom, or borrow one, and make measurements on specific plans of their choice. NPL will report the measured doses which can then be compared with the locally expected doses.

Don’t see what you are looking for? Our diverse skill set enables us to provide bespoke solutions. Please contact us to discuss your requirements

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Find out more about NPL’s Radiotherapy and diagnostic services

Find out more about NPL's Alanine dosimeter reference service

Find out more about NPL's  Medical physics research

Find out more about NPL's Linac and TPS commissioning service

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