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Carbon ions against cancer: more precise dosage becomes possible in ion beam therapy

Together with colleagues from Heidelberg, PTB physicists perform exact radiation measurements and create the basis for a more exact dosage in cancer therapy


Researchers have made an important step towards further increasing accuracy when tumors are irradiated by means of carbon ions. With the aid of precise investigations carried out by the Physikalisch-Technische Bundesanstalt (PTB), it was possible to considerably improve the measurement of the absorbed dose by a factor of three. The Deutsches Krebsforschungszentrum (DKFZ) and the Heidelberger Ionenstrahl-Therapiezentrum HIT (Heidelberg Ion-Beam Therapy Center) also participated in this research project. The first results have recently been published in the scientific journal Physics in Medicine and Biology. 

Concerning the three-dimensional irradiation of tumors, a special treatment method at the Heidelberg Ion-Beam Therapy Center (HIT) allows a precision, that has not been achieved before. In addition to the exact placement of the bundles of rays, also the exact dosage is of great importance. Picture: Universitätsklinikum Heidelberg, Download: www.klinikum.uni-heidelberg.de/Gantry-Pressebilder-Stand-Oktober-2012.129328.0.html

Compared to conventional types of irradiation, irradiation by means of carbon ions may offer an additional chance for healing, as it can be used to position the radiation dose very precisely and to spare the surrounding tissue as much as possible. This is of particular interest for deep-seated tumors and for tumors surrounded by particularly radiation-sensitive tissue. However, dosimetry of such ion beams has, to this date, not yet achieved the same precision as dosimetry of conventional, high-energy photon beams.

In clinical dosimetry, calibrated detectors – so-called ionization chambers – are normally used to measure the absorbed dose of the radiation applied. However, ionization chambers respond differently to different types of radiation. Depending on the type of radiation (Q), a correction factor k must be taken into account for correction. Until now, this so-called kQ factor has had a measurement uncertainty of approximately 3 % when using carbon ions, which was three times higher than in the case of high-energy photons. The researchers' aim was to eliminate this difference and to reduce the measurement uncertainty of ionization chambers – when carbon ions are used – to 1 %.

"So far, the correction factors used for daily routines in hospitals have been calculated ones – as reliable data that have been obtained in experiments are lacking. For the first time, we have now been able to show that this factor can actually be measured with a much smaller uncertainty", explains the author of the scientific publication, Julia-Maria Osinga-Blättermann. This was achieved by means of a transportable water calorimeter used by PTB scientists to exactly measure the absorbed dose to water and to experimentally determine the kQ factor for different ionization chambers. if

Contact at PTB:

Dr. Achim Krauss, Head of PTB Working Group 6.23 Unit of Absorbed Dose to Water

Phone: +49 (0)531 592-6230, e-mail:achim.krauss(at)ptb.de

Original scientific publication:

J-M Osinga-Blättermann, S Brons, S Greilich, O Jäkel and A Krauss: “Direct determination of k Q for Farmer-type ionization chambers in a clinical scanned carbon ion beam using water calorimetry”, Physics in Medicine and Biology, Volume 62, Number 6