Logo of the Physikalisch-Technische Bundesanstalt

Dosimetry for combined MR irradiation devices


Modern methods of external radiation therapy
are aimed at selecting the irradiation parameters
in such a way that as large an effect as possible is
achieved in the tumor volume while the surrounding,
healthy tissue is optimally protected. This dose
conformity in the target volume becomes possible
only by the use of imaging procedures. The combination
of an irradiation system with an imaging
procedure – such as magnetic resonance tomography
(MRT) – allows time-dependent changes of the
anatomy to be taken into account. This new development
can improve the chances of success of radiation
therapy, e.g. when tumors are irradiated which
move strongly due to breathing or due to the heart
beat. MR-guided radiation therapy, however, also
brings about a series of new challenges. A concrete
example of this is dosimetry in combined MR irradiation

Different forms of alanine detectors. For dosimetry in combined MR irradiation devices, the palette-shaped detectors are to be used.

ESR spectrometer is shown which is used to evaluate the alanine detectors.

The response of detectors which are usually used in dosimetry for radiation therapy, changes by the magnetic field of the MRT. For quality assurance, a consequence of this is that dosimetry protocols and uncertainties specified in them are not directly applicable. Safe use of MR irradiation devices for routine treatment of patients is, therefore, not possible. PTB wants to contribute to improving this situation and, ultimately, to make traceable dosimetry on MR irradiation devices possible. To this end, PTB is engaged in German and European research projects. A DFG project will comprise investigations in which alanine pellets are used as dose detectors which are evaluated with electron-spin resonance (ESR). The Departments “Dosimetry for Radiation Therapy and Diagnostic Radiology” and “Medical Metrology” are participating in this project.