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 and brachytherapy. The JRP-Consortium brings together leading European national metrology institutes and designated institutes. The project is jointly funded by the EMRP participating countries within the EURAMET and 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, and lack of traceability to established clinical reference dosimetry and primary standards makes it more difficult to meet the requirement of ICRU Report 24. The main reasons for this are the lack of primary standards of absorbed dose to water; the gap between the standard reference and clinical conditions laying emphasis on the need for quality controls; and in vivo dosimetry methods which should be easier to handle and more accurate.
In order to improve the situation it is necessary to develop all steps of the metrological chain from the primary standards through to verification of the dose in and around the tumour, namely: developing new primary standards of absorbed dose to water; studying new detectors and improving the knowledge of the characteristics of existing detectors useable for quality control and in vivo dosimetry; and publishing guide lines of good practice on their use.
To achieve these goals, the first stage of this project is to develop new primary standards 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 and for hadron especially for scanned beams. These new standards are based on calorimetric and 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 and energy responses, perturbation factors, linearity, homogeneity and spatial resolution depending on the transfer dosemeters and their calibration protocols are also studied to finally propose robust protocol for in vivo dosimetry and quality controls and 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 and storage film, EPID and gel) has been chosen in order to cover the need for point, 2D and 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 and 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 and 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 standard, and 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 and convenient tools available for quality control and 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 and will be finished in May 2015.
Summary of the scientific and technical objectives
"Develop and compare new references in term of absorbed dose to water for medium x-ray energies”
This objective is covered by WP1: 2 new primary standards based on different methods (calorimetry and ionometry) will be developed therefore enabling a bias (if any) due to a particular technique to be identified, standard 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 standards will be written and compared to the former ones based on air kerma.
“Study new integral quantities for the characterisation of high energy x-rays for Stereotactic RadioSurgery and RadioTherapy and Imaging Modulated RadioTherapy including a new quality index, new calibration and transfer methods in static and dynamic modes related to treatment conditions and the option for a TPS beam model parameter”
This objective is covered by WP2 by the study of the integral quantity, new quality index and new calibration and transfer methods for static mode. Verifications in dynamic mode are covered in WP5 and WP6 for example with alanine/ESR and gel dosimetry.
“Improve the consistency and traceability of proton and carbon ion beams, in particular novel types such as scanned particle beams"
This objective is covered by WP3 where both primary and secondary standard are addressed.
“Develop traceable measurement system for the verification of dose and distribution in complex radiation fields with strong variations of dose and small fields, and which is useable for the verification of treatment planning systems”
WP5 and WP6 include the study and the optimisation of dosimeters able to make measurements in 1D, 2D and 3D. The development and/or improvement of methods for internal and external quality controls and 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 and avoiding the use of radioactive isotopes. WP4 deals with the lack of a metrological chain, from the primary standard to the end user’s calibration and treatment verification, for this new treatment modality.