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Research project for fundamental improvements in radiation therapy: by means of a microbeam and nanodosimetry


In cancer therapy with ionizing radiation, the quantity of radiation absorbed by the tissue is expressed as "absorbed dose to water" in the SI unit "gray". For some novel and advantageous irradiation methods, however, various additional factors are necessary in order to take the increased biological effectiveness of, e.g., ion beams – as compared to conventional photon radiation – into account.

This project gathers leading groups of experts from
several European metrology and research institutes
in order to develop new and harmonizing concepts
for the dosimetry of different radiation qualities (from
sparsely to densely ionizing). These concepts are to
be based on measurable quantities of the particle track
structure and to correlate with the biological effects of
the radiation (e.g. the killing of tumour cells). In the future,
it should facilitate the comparison of clinical results of
different radiotherapies and optimize treatment plans by
selecting or combining the different types of radiation.

The main working groups are:

  1. Microdosimetry: Direct measurement methods for the radiation quality
  2. Nanodosimetry: Determination of the particle tracks and ionizations at the DNA level
  3. Indirect effects: Measurement of chemical effects due to radiation
  4. Radiation biology: Measurements of initial and late DNA damage in cells
  5. Simulation models: Description and quantification of physical and biological radiation effects

Biological data concerning the verification of the predictions of the simulation models are generated at PTB's microbeam within the scope of Working Group 4. These data are, on the one hand, the number of double strand breaks produced initially per particle track in living cells. These are made visible and are analyzed by biologists from France as so-called γ-H2AX foci. On the other hand, biologists from Italy and Portugal quantify the results of the cellular repair and the survival of cells. The particular role of the microbeam is that ions are focussed on a few thousandths of a millimetre and that each cell nucleus is irradiated selectively. Hereby, the number of particles per cell is measured and precisely controlled by means of a fast deflector, so that each cell nucleus is hit by exactly one ion or by a pre-defined number of ions. The use of different ions and ion energies enables us to measure the effects of different radiation qualities. Alpha particles with a high linear energy transfer (LET) from approx. 36 keV/µm to 160 keV/µm are used to investigate the effects of densely ionizing particles comparable to carbon ions in heavy-ion therapy. With energetic protons, in contrast, the effects of sparsely ionizing radiation with a low LET of about 5 keV/µm to 20 keV/µm are investigated.

This work is carried out within EMRP (European Metrology Research Programme) Joint Research Project SIB06 BioQuaRT. The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union.