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discovered 02_2012

discovered 02.12 FOCUS WWW.Hzdr.DE Two are better than one Nowadays, radiation therapy is typically administered over the course of several weeks, with the absolute dose split into individual daily doses. For each respective tumor, the radiation oncologist prescribes both the target volume and the required dose, and the medical physicist makes sure that the absolute dose, which is dependent upon both the physical form of radiation and the hospital‘s particular type of accelerator, ultimately makes its way to where the tumor is. The laser accelerator-generated proton beams consist of ultrashort, high-intensity pulses and present a major challenge for the Dresden scientists who are looking to record the exact dose immediately and in real-time. To this end, they employ two different methods – one for measuring the absolute dose, the other for real-time surveillance (known as dose monitoring). Using two different independent measuring systems, one of the things they developed was a special device for determining the exact radiation dose for the cells. In the case of the experiments with SKX cells at the HZDR, they were on the order of 0.5 to 4 Gray – a range that is especially relevant to clinical application of proton beams. The result: a dose-response curve, which plots cellular damage as a function of dosage. “We finished the first trial using laser-based precision radiation, which is comparable to the current gold standard for conventional accelerators used in medicine,“ explain Schramm and Pawelke – a real highlight of their collaborative effort and, at the same time, a research highlight! “We have not been able to observe any problems with efficacy, nor did we expect to find any evidence of it. Which means that the proton beams from the compact laser have the same effect as those from a large accelerator like, for instance, the one at the Heidelberg Ion-Beam Therapy Center. And that‘s a good thing, as it spares us having to do a lot more research, allowing us instead to continue to develop the laser accelerator more quickly, getting it ready for patient application.“ Many more experiments using different types of tumor cells have yet to be performed, but for now what‘s important is enhancing the DRACO laser’s performance. DRACO and PENELOPE The flying dragon and Odysseus‘ faithful wife, who was condemned to wait for her husband‘s return home for twenty long years - clearly, the HZDR laser physicists had considered these two mythological references when naming their lasers. Whereas PENELOPE, the new petawatt facility, is, as of now, still in the building stages (the designated rooms in the ELBE Radiation Source, which were expanded especially to house PENELOPE, are already eagerly awaiting the new equipment’s arrival), 150-terawatt DRACO has already made research waves. The plan is to enhance DRACO’s capacity to 500 terawatts by adding an additional amplifier stage. Which means DRACO will reach a new order of magnitude, becoming one of the world‘s top performing lasers. After all, 500 terawatts exceed the performance of all of the world‘s power plants taken together, albeit only for an ultrashort, 30-femtosecond moment. As a modern-day accelerator technology, light-based particle acceleration offers several major advantages over conventional facilities, since the accelerator track is shorter by several orders of magnitude and associated cost potentially lower – yet energy values are still insufficient for successful application in laser-based proton beam cancer therapy. As part of the expansion stage, the ultimate goal is for DRACO to generate proton beams with energies that are suitable for radiation treatment of small animal models. There is only one system likely to compare to DRACO, and that is the high-performance laser at the Lawrence Berkeley National Laboratory in California, USA. That particular lab‘s laser system, however, is used for basic science research and not for application to cancer therapy. One other laser that deserves mentioning is one operated in South Korea, albeit at a very low proton pulse rate of repetition. “With the DRACO expansion stage, we have realized exactly what we set out to do. And we are once again breaking new ground by incorporating two crystals into the new amplifier stage, which did not as such exist even a few short years ago,“ explains Ulrich Schramm, head of the Laser-Particle Acceleration Division at the HZDR. At a diameter of twelve centimeters, the crystals are visually perfect and are only manufactured by a single company. Whereas initial DRACO CELLULAR DAMAGE: The image shows three cell nuclei following their irradiation with laser-accelerated protons using doses of 1.5, 2.7, and 4.1 Gray, respectively. The double-strand breaks in the DNA molecule (shown here in yellow) are a measure of cellular damage. The number of double-strand breaks increases as a function of the radiation dose.