The EURAMET Technical Committee for ionising radiation (TC-IR)
Roadmap for 2020:
TC-IR Roadmap
Novel dosimetry concept for ionising radiation interaction with matter (Hans Rabus, PTB)
Drivers and Challenges
a. Medical applications – radiotherapy:
In the past (and for several treatment modalities also still in the present), the major metrological challenge for medical applications of ionising radiation for therapeutic purposes was to establish a QA system based on standardised protocols for dosage quantification (i.e. determination of absorbed dose to water). The extensive progress made in this respect during recent years has led to a situation where today for most mainstream treatment modalities further efforts to reduce uncertainties of primary measurement standards are in vain as they will not lead to an improvement of the treatment capabilities.
Furthermore, the comparison of different treatment modalities based on absorbed dose to water protocols is still very difficult to impossible. Major hampering factors are:
o The different biological effectiveness of different radiation qualities on cancerous and healthy tissue.
o The large span of different irradiation conditions when comparing external beam therapy with photons and BNCT or radionuclide therapy using alpha emitters.
o Different patient radio-sensitivity owing to which equivalent dosage (in terms of absorbed dose to water) does not imply equivalent treatment.
This dissatisfactory situation has prompted the ESTRO to formulate her 2020 vision of individualised radio-therapeutic treatment using a multi-disciplinary approach which involves couple of metrological challenges:
o A dosimetric concept that facilitates the combination of different treatment modalities, particularly of radionuclide therapy and EBT, but also the confounding influence of imaging techniques in IGRT, such as ionising radiation effect in magnetic fields.
o Providing metrology support for improved individualized treatment planning based on the virtual human approach, where also basic parameters entering the treatment planning may be individually derived from the diagnostic measurements preceding the treatment (e.g. conversion of Hounsdfield units radiation transport quantities).
o Development of a unified dosimetric concept for radiation quality that is not based on the global-view specification how the radiation is produced or administered but rather reflects the local properties of the radiation field and thus allows quantifying radiation effects at the microscopic level and at the level of individual cells or small compartments of tissue including early biological effects.
o Developing a measurement protocol for biological effects, e.g. quantifying the ‘efficiency’ of cell repair mechanisms, to provide a metrology support for the application of dose fractionation and radio-sensitizers.
o Measuring individual radio-sensitivity, enabling treatment plans based on patient-specific rather than population-averaged dose-effect curves.
b. The present system of physical operational quantities in dosimetry is based on phenomenological weighting factors that are almost exclusively based on epidemiological evidence. Hence it require an extrapolation into the low-dose exposure regime (which is most important in radiation protection) based on model assumptions that cannot be tested experimentally, as the range of applicability of biological dosimetry is also limited to sufficiently high doses. Furthermore, for radioactive agents like the ubiquous Radon which emit short-range alpha particles a dose concept based on macroscopic averages is not strictly applicable.
Metrological challenges:
o Extension of the range of applicability of biological dosimetry toward lower doses by enhancing the through-put and reliability of biological assays through better control of experimental conditions by application of metrology.
o Establishing a traceability chain of biological dosimetry to physical standards of ionising radiation or, alternatively, develop biological standard systems.
c. The advance of new materials in nano-technology and the development of advanced electronics produce structures of geometrical dimensions of particle track diameters that are potentially very vulnerable when exposed particularly to densely ionising radiation fields as are present in space application, at fusion reactor experiments but also in accelerator-based treatment units in clinics. A quantitative measure of the risk of inducing a severe damage that can lead to component failure or loss does not exist. Radiation hardness or reliability of such components is typically assessed on a phenomenological basis in destructive tests. A measurand quantifying damage due to radiation interaction in nano-tech components, electronics and bio-systems would give a means to characterise the potential of different radiation qualities to damage such systems and would allow a targeted development of more radiation-robust components and hence have a significant impact on the speed of progress in this fields as well as on financial resources hitherto wasted in destructive testing.
Targets
a. Medical applications of ionising radiation:
Facilitate combination of different treatment modalities and optimisation of image-guided techniques in radiotherapy, the further development of radio-sensitizers and patient-specific treatment planning based on quantitative measures of individual radiation sensitivity. Thus providing basis for higher cure rates in radiotherapy with simultaneous reduction of side effects, a sustained improvements of patients’ quality of life after treatment and an overall cost-reduction to the health system.
b. Metrology support for new or redefined operational quantities in dosimetry. Improved standards for occupational radiation protection. Better data base for decision maker and regulatory bodies in the field of radiation protection. Reduction of radiation risk to occupationally exposed personnel and the general public.
c. Facilitation the development of radiation-resistant nano-electronics and other nano-structured devices as well reliable biological-cell based production techniques. Augmenting the safety of space missions and the reliability and dependability of satellite-based infrastructure like GPS, global communication, etc.
d. Realisation of the components of the virtual human that are related to ionising radiation.
Deliverables
a. New concepts for quantifying radiation effects in terms of radiation field properties and time and space correlations of the radiation interaction events (e.g. micro- and nanodosimetry).
b. Quantitative and comprehensive characterisation of the correlation between microscopic particle track structure with the radiation damage to microscopic structures like biological cells or micro- and nano-electronics.
c. Comprehensive multi scale characterisation of charged particle tracks and validated biological models relating these microscopic properties to macroscopic effects as to be used e.g. in treatment planning.
d. A novel unified concept of radiation quality based on measurable properties of the particle track structure; its experimental realisation and implementation with ‘primary standards’ and traceable easy-to-use end-user measurement devices.
e. Dosimetric concepts (and measurement techniques for their realisation) quantifying radiation effects at the microscopic level and at the level of individual cells or small compartments of tissue.
f. Measurand(s) quantifying the damage to new materials in nano-technology, advanced electronics and biosystems.
g. Measurement quantity(ies) related to biological effectiveness of ionising radiation for use in radiation therapy and for radiation protection purposes.
h. Development of biological standards in terms of cell systems and in terms of metrology-supported biological protocols and experimental procedures. E.g. standardized (‘traceable’) cell survival curves
Technologies
To be completed
Enabling Science
To be completed.
If you want more information please contact the roadmap pilot or TC-IR Chair.