How strongly does tissue decelerate the therapeutic heavy ion beam?

Jul 15, 2014

Physikalisch-Technische Bundesanstalt has developed a method for the more exact dosing of heavy ion irradiation in the case of cancer.

Irradiation with is suitable in particular for patients suffering from cancer with tumours which are difficult to access, for example in the brain. These particles hardly damage the penetrated tissue, but can be used in such a way that they deliver their maximum energy only directly at the target: the tumour. Research in this relatively new therapy method is focussed again and again on the exact dosing: how must the radiation parameters be set in order to destroy the cancerous cells "on the spot" with as low a damage as possible to the surrounding tissue? The answer depends decisively on the extent to which the ions can be decelerated by body tissue on their way to the tumour. Scientists of the Physikalisch-Technische Bundesanstalt (PTB) have established an experiment for the more exact determination of the stopping power of tissue for carbon ions in the therapeutically relevant area which is so far unique worldwide. Although the measurement data so far available must still become more exact, the following can already be said: The method works and can, in future, contribute to clearly improving the dosing for cancer therapy with carbon ions. The first results have recently been published in the magazine "Physics in Medicine and Biology".

Human tissue mainly consists of water. It can, therefore, be simulated well in in which form accelerated ions can be stopped on their way and at which target they deliver their maximum energy quantity – at least theoretically, because up to now experimental data has existed only for water vapour. Scientists, however, assume: If the aggregate state is neglected, the data determined for the determination of the radiation dose become too imprecise.

Within the scope of the doctoral thesis of J. M. Rahm, PTB scientists have now succeeded for the first time in determining the stopping power of liquid water for carbon ions with kinetic energies in the range of the maximum energy dissipation by experiment. The first results actually indicate that carbon ions are less strongly stopped in liquid water, related per molecule, than in water vapour. As soon as more exact data are available, the findings will be included in the calibration of ionization chambers which are used to determine the dose in therapy planning. At present, the Heidelberg Ion-Beam Therapy Center (HIT) is the only institution in Europe which irradiates patients with heavy ions.

The procedure applied by the researchers is based on a method which originates from nuclear physics: the Inverted Doppler Shift Attenuation Method. While the carbon ions excited by a nuclear reaction move through the water volume, they are stopped and fall back into their ground state. The energy distribution of the gamma quanta emitted thereby is recorded with the aid of an ultra-pure germanium detector. The Doppler effect, which leads to the displacement of the gamma energy, and the exponential-decay law allow the development of the velocity of the carbon ions with time to be pursued and, thus, conclusions on the stopping process to be drawn.

Explore further: Helium ions may provide superior, better-targeted treatment in pediatric radiotherapy

More information: J. M. Rahm, W. Y. Baek, H. Rabus and H. Hofsäss: "Stopping power of liquid water for carbon ions in the energy range between 1 MeV and 6 MeV." Phys. Med. Biol. 59 3683 (2014)

add to favorites email to friend print save as pdf

Related Stories

From graphite to water

Sep 17, 2013

Scientists from the National Physical Laboratory (NPL), in collaboration with researchers in Belgium and Italy, have published research that could help provide a primary standard for dose measurements of ...

Hollow optical fibers for UV light

Jul 02, 2014

(Physikalisch-Technische Bundesanstalt (PTB)) Researchers from the Max Planck Institute for the Science of Light in Erlangen/Germany and of the QUEST Institute, based at the Physikalisch-Technische Bundesanstalt, ...

Fundamental research improves oil extraction efficiency

May 23, 2014

We are currently successful in extracting approximately one third of the oil from oil fields. The reason for this low figure is that a large proportion of the oil remains trapped in the rock. It was already ...

Recommended for you

New terahertz device could strengthen security

Nov 21, 2014

We are all familiar with the hassles that accompany air travel. We shuffle through long lines, remove our shoes, and carry liquids in regulation-sized tubes. And even after all the effort, we still wonder if these procedures ...

CERN makes public first data of LHC experiments

Nov 21, 2014

CERN today launched its Open Data Portal where data from real collision events, produced by experiments at the Large Hadron Collider (LHC) will for the first time be made openly available to all. It is expected ...

New technique allows ultrasound to penetrate bone, metal

Nov 20, 2014

Researchers from North Carolina State University have developed a technique that allows ultrasound to penetrate bone or metal, using customized structures that offset the distortion usually caused by these ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

EyeNStein
not rated yet Jul 15, 2014
If the carbon ions emit gamma radiation at the target: Then a 3D array of gamma cameras could map the target accuracy in real time in the patient and servo-adjust for max therapeutic impact.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.