The Joint Research Project "Metrology for radiotherapy using complex radiation fields" is a three-year project aiming to improve the metrology of ionizing radiation in external beam radiotherapy brachytherapy. The JRP-Consortium brings together leading European national metrology institutes designated institutes. The project is jointly funded by the EMRP participating countries within the EURAMET the European Union.
Advancing technology has enabled the introduction of complex forms of radiotherapy in the treatment of cancer, in which dose is delivered in ways that are far removed from established reference dosimetry. While treated volumes can now conform closely to the defined target, so reducing damage to surrounding normal tissue, the accuracy with which the dose is delivered may fall short of the requirements given by ICRU Report 24 (uncertainty of 5% at the 95% confidence level on the dose in the target volume).
The overall dose targeting the affected areas has significant implications for the results. Thus, too low dose in the target volume increases the chance of treatment failure through recurrence of the cancer, lack of traceability to established clinical reference dosimetry primary st ards makes it more difficult to meet the requirement of ICRU Report 24. The main reasons for this are the lack of primary st ards of absorbed dose to water; the gap between the st ard reference clinical conditions laying emphasis on the need for quality controls; in vivo dosimetry methods which should be easier to h le more accurate.
In order to improve the situation it is necessary to develop all steps of the metrological chain from the primary st ards through to verification of the dose in around the tumour, namely: developing new primary st ards of absorbed dose to water; studying new detectors improving the knowledge of the characteristics of existing detectors useable for quality control in vivo dosimetry; publishing guide lines of good practice on their use.
To achieve these goals, the first stage of this project is to develop new primary st ards where a lack of references complying with the international protocol is identified i.e. for new low energy X ray source for brachytherapy, for medium energy X rays, for small size high energy X-rays beams for hadron especially for scanned beams. These new st ards are based on calorimetric ion chamber techniques for which new developments are necessary. For high energy X-rays in radiotherapy, the possibility to measure a new integral quantity similar to dose area product is evaluated. Whatever is the radiation beams; dosimetric characteristics i.e. directional energy responses, perturbation factors, linearity, homogeneity spatial resolution depending on the transfer dosemeters their calibration protocols are also studied to finally propose robust protocol for in vivo dosimetry quality controls to evaluate the possibility for assessing absorbed dose to water at a point in small beams; the dosemeters which will be studied (ion chambers, silicon diode, CVD diamond, ESR/Alanine, radio-chromic storage film, EPID gel) has been chosen in order to cover the need for point, 2D 3D measurements. This research work has been split into work packages (WP) which are described on this website.
The project is aimed at enabling the international codes of practice for radiotherapy to be updated, producing good practice guidelines for quality controls in vivo dosimetry that will be distributed to the radiotherapy services. By the end of this project, it will be possible to use absorbed dose to water to disseminate it for all radiations studied within the frame of the JRP. The first step towards the application of an integral quantity for very small X-ray fields (i.e. establishment of reference, new quality index, secondary st ard, identify the scope for using integral quantity in Treatment Planning System –TPS- calculation) will have been completely evaluated. The medical physicists will have more reliable convenient tools available for quality control in vivo dosimetry allowing validation of the treatment plan. A workshop will be organised by the end of the project. This workshop will be open to all the stakeholders. Numerous papers will be proposed to peer reviewed journals to disseminate the results. Many stakeholders are involved in the work packages.
The project started in June 2012 will be finished in May 2015.
Summary of the scientific technical objectives
"Develop compare new references in term of absorbed dose to water for medium x-ray energies”
This objective is covered by WP1: 2 new primary st ards based on different methods (calorimetry ionometry) will be developed therefore enabling a bias (if any) due to a particular technique to be identified, st ard radiation qualities will be elected for transferring the reference to the end users, guidelines for a new dosimetry protocol based on absorbed dose to water primary st ards will be written compared to the former ones based on air kerma.
“Study new integral quantities for the characterisation of high energy x-rays for Stereotactic RadioSurgery RadioTherapy Imaging Modulated RadioTherapy including a new quality index, new calibration transfer methods in static dynamic modes related to treatment conditions the option for a TPS beam model parameter”
This objective is covered by WP2 by the study of the integral quantity, new quality index new calibration transfer methods for static mode. Verifications in dynamic mode are covered in WP5 WP6 for example with alanine/ESR gel dosimetry.
“Improve the consistency traceability of proton carbon ion beams, in particular novel types such as scanned particle beams"
This objective is covered by WP3 where both primary secondary st ard are addressed.
“Develop traceable measurement system for the verification of dose distribution in complex radiation fields with strong variations of dose small fields, which is useable for the verification of treatment planning systems”
WP5 WP6 include the study the optimisation of dosimeters able to make measurements in 1D, 2D 3D. The development /or improvement of methods for internal external quality controls for in vivo dosimetry based on these dosimeters are included. Guidelines for these methods will be written.
"The use of low energy x-rays for brachytherapy"
New low energy x-ray generators are now available for improving the efficiency of low energy brachytherapy treatments avoiding the use of radioactive isotopes. WP4 deals with the lack of a metrological chain, from the primary st ard to the end user’s calibration treatment verification, for this new treatment modality.