Radiation Dosimetry Group & RadiotherapyOpening of the joint NPL-Elekta linac

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Clinical linacs at NPL

The dose in every radiotherapy treatment provided by UK hospitals is determined by instruments calibrated directly against the NPL primary standard. This results in a world-leading national dosimetry system that underpins the rapidly expanding variety of radiotherapy technologies.

The first clinical linear accelerator (linac) to be installed at NPL was manufactured by Elekta and is the same as those installed in many hospitals to provide radiotherapy treatments. However unlike any hospital machine, the one at NPL can be reconfigured to deliver seven different photon energies, instead of the standard two or three energies found on a clinical machine, and ten electron energies. It can also deliver image-guided 4D radiotherapy, in which tumours can be targeted more accurately.

The second clinical linac represents the culmination of a unique partnership between BIS, Elekta and NPL. It will be maintained by Elekta and fitted with the newest technology ahead of its introduction onto the market. The new linac will provide excellent research opportunities to drive forward the development of measurement science in the area of radiation dosimetry. This facility will extend the National Measurement System’s commitment to respond to healthcare challenges; specifically improving the treatment of cancer.

The first clinical linac, opened in 2008.

Elekta Synergy® linac

7 photon energies: • 4 – 25 MV

10 electron energies: • 4 – 22 MeV

MLCi2 multi-leaf collimator (80 interdigitating leaves)

portal imaging (iViewGT)

cone beam CT (XVI)

record & verify (IMPAC / MOSAIQ)

Pinnacle3 Treatment Planning System

The second clinical linac, opened in 2013.

Elekta Versa HD™ linac

7 photon energies:

• 4 – 25 MV including flattening filter free beams

9 electron energies:

• 4 – 20 MeV

Agility™ head (160 interdigitating leaves)

portal imaging (iViewGT)

clinical couch

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The facility was essential to the development at NPL of the world’s first absorbed dose primary standards and calibration services for radiotherapy using a range of high-energy beams, launched in the 1980s and 1990s. Investigations into the dependence of megavoltage beam quality and calibration coefficients on x-ray beam filtration remain relevant today, as increasing numbers of cancer patients are treated with flattening filter free beams.

Other research and development activities carried out include: radiation hardness testing of materials, components and instruments for the aerospace, telecommunications, electronics and defence industries.

The NPL research linac (1975 – 2012)

The first linac at NPL was a dosimetry research facility, opened in 1975. The machine was extensively modified before installation at NPL; having previously been used by the UKAEA for industrial processing. Measurements were made either directly in the electron beams, of nominal energy between 4 MeV and 19 MeV, or in the x-rays emerging from a tungsten target.

Whereas linacs nowadays are almost always computer controlled, this machine required close attention to parameters such as the frequency and phase of the RF, the timing and strength of the pulses from the electron gun, and the steering and focusing of the beam to the targets. Performing high-quality research was, then, a complex operation usually requiring the attendance of several staff, and as it aged into the 1990s and after 2000, this became more difficult and costly.

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Research Collaborations

Small field and complex field dosimetryNPL is active in developments needed for dosimetry and beam quality specification in radiotherapy techniques like stereotactic radiosurgery and IMRT. Collaborations have included projects sponsored by the European Metrology Research Programme (EMRP), and working with the IPEM and IAEA on producing recommendations for small and complex field dosimetry. An absorbed dose calibration service based on alanine has been developed in collaboration with UK and international centres for TomoTherapy and CyberKnife machines.

Light-ion dosimetryNPL is developing a primary standard of absorbed dose for protons and light ions based on a graphite calorimeter; anticipating the arrival of proton therapy in the UK. Characterisation of the dose response of ion chambers, alanine, radiochromic film and novel microdosimetric devices to light ions is performed in collaboration with the Clatterbridge Cancer Centre, the University of Surrey, The Royal Surrey County Hospital and the University of Aarhus, Denmark.

Biologically relevant radiotherapy quantitiesThe rapid increase of new technologies in radiotherapy raises the need for new dosimetric concepts to account for the biological effectiveness of the dose delivered and the modality used. Complex IMRT treatments, proton beams and MRI-Linac facilities are some of the new techniques which offer potential benefits but significantly alter the dose distribution pattern. NPL is involved in several projects aimed to link the spatio-temporal aspect of dose deposition (physical processes) to cellular/tissue response (biological processes). Identification and quantification of suitable weighting factors will ensure consistency and optimization of dose assessment and prescription across the different modalities.

Dosimetry for molecular radionuclide therapy (MRT)NPL is well aware of the need for more accurate measurement of the absorbed dose from therapeutic radiopharmaceuticals to the target tissue and critical normal tissues when used for medical therapy. In response, an exploratory project has started in collaboration with UK nuclear medicine departments to set MRT dosimetry on a more rigorous basis, leading to more accurate methods, and the possibility of the clinical implementation of a consistent dosimetry protocol. The project will be investigating quantitative imaging, direct measurement of absorbed dose from radionuclides, and uncertainty analysis.

NPL Proton Physics Research & Implementation Group (PPRIG) The new NPL Proton Physics Research & Implementation Group (PPRIG) was formed in 2013 in response to the announcement that the UK Government is funding two new Proton Beam Therapy Centres at UCLH and the Christie. The group is made up of representatives from NPL, UCLH, the Christie, the Clatterbridge Cancer Centre, UCL, University Hospitals Birmingham and St James’s University Hospital Leeds.

Pre-clinical quality assuranceNPL is part of a nationwide CTRad initiative for quality assurance in pre-clinical studies. Pre-clinical investigations are essential to developments that are expected to drive forward the practice of radiotherapy. However, the knowledge gained from pre-clinical experimentation is only sound if supported by precise and systematic methodologies. With the increasing range and complexity of new irradiation modalities, a rigorous programme of coordinated pre-clinical quality assurance, at all levels of experimental sophistication, is imperative. The NCRI CTRad initiative aims initially to establish quality assurance standards which extend to practices and guidelines that can address everything from cell culture irradiation to small animal radiation research platforms in order to meaningfully simulate the complexity of radiotherapy treatments.

Steering groupEight clinical scientists act as a steering group to provide impartial advice to NPL on: Problems in the measurement and verification of dose delivered to radiotherapy patients that could usefully be addressed by NPL; Progress of current RT projects at NPL, including technical/scientific advice; Development of new RT research projects; Maintenance of effective working relationships between NPL and the RT community.

Radiotherapy trials QA groupNPL is working with the RTTQA group on measurements to support clinical trial dosimetry audit. Recent work has included a national audit of rotational IMRT, which included all centres who are offering this technique in the UK.

Medical physics traineeA radiotherapy physicist trainee registered on the NHS Scientist Training Programme is currently undertaking an elective placement of 4-6 weeks in the Radiation Dosimetry Group. The placement includes beam data acquisition for wedge beam modelling in Pinnacle, 3D Conformal Treatment Plan creation using the NPL Pinnacle treatment planning workstation, as well as familiarisation with chamber calibration procedures at the NPL.

For more information please contact:Rebecca Nutbrown Tel: 020 8943 6473 rebecca.nutbrown@npl.co.uk

Training courses and meetings Reaching a Consensus on Verification of Radiotherapy Delivery – 13th December 2013NPL, RTTQA and IPEM RTSIG (IDA group) are holding a one-day meeting on radiotherapy audit.

The aim of this meeting is to present and discuss current and future audits, with a focus on the strategies for co-ordination which exist and can be developed between the RTTQA, IPEM and NPL, as well as any other independent groups which may be active. This will reinforce the collaborative and coordinated profile of radiotherapy audit in the UK in an international setting, which it is hoped will strengthen the ability of UK centres to join international trials with minimal QA requirements.

Workshop on Proton Therapy Physics – 12th-13th March 2014PPRIG is pleased to announce that a two day Workshop on Proton Therapy Physics will be hosted at NPL on the 12th-13th March 2014. The aims of the workshop will be to initiate discussions between experts in the field; develop links and collaborations; as well as to inform relative newcomers to the field, providing access to a network of experts. It is anticipated that this workshop will help to stimulate more collaborative research in the field of proton therapy physics which would ultimately support the two new national centres. The workshop will cover: Relative and Absolute Dosimetry of Proton Beams, Detector Instrumentation, QA & Delivery Verification, Proton Imaging, Treatment Planning, Monte Carlo for Proton Therapy Physics and Radiobiology. Invited lectures will be given by Dr Richard Amos (UCLH), Professor Marco Durante (GSI Helmholtz Centre for Heavy Ion Research), Professor Phil Evans (University of Surrey), Professor Uwe Oelfke (The Institute of Cancer Research), Professor Harald Paganetti (Massachusetts General Hospital and Harvard Medical School), Dr Hugo Palmans (NPL) and Professor Ken Peach (John Adams Institute for Accelerator Science). Additionally there will be opportunities to present proffered papers and posters.

Training Day on Dosimetry for Advanced Radiotherapy Techniques – 13th May 2014NPL is holding a training day on Dosimetry for Advanced Radiotherapy Techniques on the 13th May 2014. This event will cover training for: small and composite field dosimetry; dosimetry for FFF beams; and future dosimetry issues, such as for protons, hadrons and MR linacs.

Practical Course in Reference Dosimetry – annually in JanuaryThis popular hands-on training course is primarily aimed at trainee radiotherapy physicists, but would also benefit anyone wishing to improve their practical dosimetry techniques. The course is presented by members of NPL’s Radiation Dosimetry Group together with representatives from clinical radiotherapy departments who have extensive experience in reference dosimetry and its application in clinical radiotherapy.

Modelling of shielding for new clinical linac

When replacing NPL’s research linac with a new Elekta clinical machine it was necessary to re-assess the shielding requirements; a situation often encountered for radiotherapy facilities when undergoing a change of use. These calculations were carried out using Monte Carlo methods, utilising and building on NPL’s strong expertise in radiation transport simulations. These simulations provide extremely detailed dose-rate maps of the entire facility and for any configuration of the machine allowing us to optimise the placement and type of additional shielding required.

NPL now offers support for hospitals and other institutions, using these techniques to evaluate the effectiveness of existing shielding when changes to treatment modalities or linac replacements are planned.

We also welcome enquiries regarding consultation or collaboration in other ionising radiation problems where modelling may be able to provide a solution.

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www.npl.co.uk/protontherapy2014

For more information please contact:

Russell Thomas Tel: 020 8943 6052 russell.thomas@npl.co.uk

For more information please contact:

Catharine Clark Tel: 020 8943 6329 catharine.clark@nhs.netwww.npl.co.uk/rtaudit2013

For more information please contact:

David Crossley Tel: 020 8943 6876 dosimetry@npl.co.ukwww.npl.co.uk/dosimetry/pcrd

For more information please contact:

www.npl.co.uk/irmodelling/David Shipley Tel: 020 8943 6252 david.shipley@npl.co.uk

For more information please contact:

Rebecca Nutbrown Tel: 020 8943 6473 rebecca.nutbrown@npl.co.ukwww.npl.co.uk/advancedrt2014

Dosimetry audits

UK dosimetry audit for HDR/PDR brachytherapyNPL is collaborating with the RTTQA Interlace trial group on a comprehensive dosimetry audit of HDR/PDR brachytherapy. A water equivalent audit phantom has been designed by physicists from both NPL and Mount Vernon Cancer Centre. The Solid Water phantom, which was built at Clatterbridge Cancer Centre, allows an accurate measurement of a point dose at 20 mm distance from the centre of a 50 mm brachytherapy line source using alanine dosimeters. The national audit is currently underway.

Reference dosimetry auditsNPL have offered on-site reference dosimetry audits for the past 17 years. Whilst these were originally NMS-funded on behalf of Radiotherapy Departments many have been directly funded, for example as an independent audit of a machine prior to release for clinical use. Routinely, audits have included MV photons, electrons, and kV x-rays; these are available on demand.

Rotational therapy auditA national audit has been carried out for rotational techniques (VMAT, TomoTherapy) in collaboration with IPEM, the Royal Surrey County Hospital and the Radiotherapy Trials QA group. The national audit findings were presented at ESTRO 2013.

Stereotactic Ablative Body Radiotherapy (SABR/SBRT) auditThis is a postal audit for SABR treatment of the lung, using an anthropomorphic phantom where measurements are made using alanine and gafchromic film. The audit is in collaboration between NPL, The Clatterbridge Cancer Centre, The Royal Surrey County Hospital, the UK SABR consortium and the RTTQA group.

Clinical linac beam data acquisition serviceLinac commissioning is a time-consuming process. NPL now offers support in the form of staff time and equipment to assist in the beam data acquisition part of commissioning.

NPL can provide:Staff on-site as required and advice on measurement technique and commissioning procedures.

Typical data acquired: Photon and electron beams Open and wedged fields Profiles and depth doses Relative output measurements

Photon and electron independent verification audits prior to release of a machine for clinical use are also available.

For more information please contact:

Russell Thomas Tel: 020 8943 6052 dosimetry@npl.co.uk

Calibration services

Calibration services are offered which support the relevant UK codes of practice, but which may also be used in conjunction with international codes. These include:

Therapy level absorbed dose and air kerma calibration service for photons (Spring each year and Autumn by arrangement)

Absorbed dose calibration service for electrons (Spring each year or on-demand)

Alanine reference dosimetry service (on-demand)

Ophthalmic eye applicator service (on-demand)

HDR Brachytherapy service (Spring-Summer each year)

New HDR brachytherapy afterloader at NPLNPL has upgraded its HDR brachytherapy calibration facility from a Nucletron microSelectron-v1 classic afterloader, which will only be supported until the end of 2013, to a new Flexitron afterloader. NPL’s existing HDR Ir-192 air kerma primary standard is currently being re-commissioned for the new Flexisource. From 2014, the HDR brachytherapy calibration service will be based on the new source type. The re-commissioning work will also be extended to NPL’s new absorbed dose standard for HDR Ir-192 which is based on a graphite calorimeter.

2611 secondary standard thimble chamberThe NPL-designed photon ‘therapy-level’ secondary standard thimble chamber is now being manufactured and supported in-house.

New chambers and a repairs service are available.

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For more information please contact:

Julia Snaith Tel: 020 8943 6337 dosimetry@npl.co.uk www.npl.co.uk/dosimetry

Graham Bass Tel: 020 8943 6503 dosimetry@npl.co.uk

National Physical LaboratoryHampton RoadTeddingtonMiddlesexTW11 0LW

www.npl.co.uk/location