First tests for lung cancer therapy with heavy ions
The heavy ion cancer therapy developed at GSI Helmholtzzentrum für Schwerionenforschung GmbH in Darmstadt has proved very successful. Thus far, however, it has primarily been used to treat brain tumours. This is because the head is one part of the body that can be kept completely stationary – a prerequisite for the ion beam, which hits cancer cells with pinpoint precision. Breast or stomach tumours are extremely frequent but more difficult to treat with an ion beam as they move as a result of respiration or digestion. Researchers at GSI have simulated these human movements and succeeded in irradiating an artificial tumour in a model of a breathing chest (thorax) for the first time.
Respiration is a very complex procedure. A person’s breathing pattern constantly changes, for example, if the individual is stressed or relaxed, coughing or even just clearing his or her throat. And in each of these situations, the diaphragm moves the lungs, and subsequently all internal organs, in and out. This means that lung tumours are constantly moving.
In order to develop a lung tumour therapy, scientists first modelled a human chest using a training skeleton. “We call the thorax model Bruce Lee,” states Dr. Robert Kaderka, biophysicist at GSI, adding that he and his team took the name from the manufacturer’s brand name for the skeleton (Skelett Bruce). The model includes skin, ribs, a spine and the target tumour. An electronic motor raises and lowers the chest to mimic respiration. “At the same time, a robot arm moves the tumour realistically in synch with the lung,” continues Kaderka.
To irradiate the tumour, the researchers first took a time-resolved CT image of the chest. This enabled them to see exactly how the tumour moved during a single breath and plan the irradiation. While the model undergoes treatment, cameras record the chest movement from outside in real time. This information is then fed into software. “The software simulates a neural network – in other words, a brain,” elaborates Associate Professor Dr. Christoph Bert, head of the medical physics group at GSI. “It learns how a specific individual breathes,” he concludes. The software then uses this data to predict the movement of the tumour in the lung and adjust the heavy ion beam in a matter of milliseconds.
The artificial tumour contains 20 ionization chambers and five radiographic films, which record whether the beam actually reaches its target to destroy harmful tumour cells. Accuracy is crucial here. If the ion beam does not hit the tumour it can damage surrounding tissue. It also means that the dose the tumour receives is too low to kill all cancer cells. The findings are still being evaluated, but the scientists are confident that the irradiation test was a success.
The cameras and software come from Milan. Matteo Seregni, PhD student at the Politecnico di Milano, and his colleagues have the necessary operational expertise. Seregni spent three months at GSI preparing the experiments. Getting a project such as this up and running in such a short space of time requires the right mix of specialists and international collaboration. The German Research Foundation and Siemens AG funded different aspects of the setup . Additional funds were provided by the EU projects European NoVel Imaging Systems for ION therapy (ENVISION) and the Union of Light-Ion Centres in Europe (ULICE).