Finding and treating tumours with protons
Is it possible to diagnose a tumour and treat it at the same time? This idea might become reality in the near future. In a joint experiment of GSI Helmholtzzentrum für Schwerionenforschung GmbH and the Technical University in Darmstadt (TUD) with the Los Alamos National Laboratory (LANL), USA, researchers showed in December 2012 that beams of fast protons could do the trick. Scientists call the combination of therapy and diagnosis "theranostics".
In the experiments at the accelerator facility in Los Alamos the scientists irradiated a mouse with fast protons. Tiny structures like the spine or the ribs are visible. Radiography of the human anthropomorphic phantom of the Matroshka experiment (developed by the Deutsches Zentrum für Luft- und Raumfahrt for dosimetry on the International Space Station) was also registered in Los Alamos using high-energy protons.
Protons are the atomic nuclei of hydrogen atoms. With aid of an accelerator they can be accelerated to high speeds. Similar to the already established x-rays in medicals diagnostics the protons can radiograph an object and generate an image of it. "Up to now inanimate objects have been examined with this technique. For example plasmas or explosions can be irradiated and one can gain an image of the movements inside", explains Dr. Dmitry Varentsov from the GSI Plasma physics department. In the experiments at Los Alamos now researchers from the GSI biophysics and plasma physics departments produced images and movies of biological samples for the first time.
"A direct treatment of a tumour with the same protons used for imaging is possible. One could precisely aim at the tumour and irradiate it with a dose of protons to destroy it (aim-and-shoot)", says Professor Marco Durante, head of GSI biophysics. "The images gained from the fast protons have a high resolution, small structures are visible. This would allow the differentiation between sensitive healthy tissue and tumour tissue in a treatment."
"The treatment would at the same time deliver an exact picture of the environment of the tumour to adjust the beam for the consecutive sessions. That is especially important when the tumour is close to sensitive areas like the brain stem or the spinal cord", says Dr. Matthias Prall from GSI biophysics who participated in the experiments with his colleagues. "One can carefully approach the critical organs and ensure that the tumour is destroyed and the healthy tissue is spared."
GSI has long-time experience in tumour therapy with carbon ions. This form of cancer treatment would benefit from the proton diagnostics as well. Until now information about the tumour is gained by diagnostics with x-rays (CT scan). The different types of tissue on the way to the tumour play an important role for the treatment planning. But x-rays penetrate the tissue differently from ion beams. The data gained from CT scan has to be converted for the planning of ion treatment. Using proton radiography for treatment planning in ion therapy would drastically reduce the range uncertainty and consequently allow to further reduce the margins of the target volume, thus sparing even more normal tissue.
In planned experiments in Fall 2013 in Los Alamos the GSI, TUD and LANL scientists want to irradiate other biological samples. They plan to diagnose and treat a tumour with this technique. That could be an artificial tumour inside the Matroshka phantom or a tumour in an animal.
"In the future, similar experiments will be possible at the accelerators of FAIR, that is currently built in international collaboration and will be connected with the existing GSI facilities", Durante gives as a prospect for the future. "FAIR will contain an experimental site for the joint use of the plasma physics and biophysics scientists. FAIR will produce protons with even higher energies than GSI and the facility in Los Alamos. This will improve the quality of the imaging and offer new perspectives for investigation of the tumour treatment."