discovered_01_2016 - Tracking the Proton Beam

WWW.HZDR.DE discovered 01.16 RESEARCH // It used to be impossible to determine how deeply proton beam therapy penetrates the body of a cancer patient. A special camera, developed by Ion Beam Applications (IBA) and clinically tested by a team of Dresden-based researchers, can solve this problem and save healthy tissue from unnecessary radiation. _ TEXT . Sascha Karberg TRACKING THE PROTON BEAM When doctors treat cancer patients with proton beams, they use what is considered the most precise radiation technology available to date. In contrast to harsh X-rays, which also harm the healthy tissue in front of, next to and behind a tumor, a proton beam can be directed in such a way that its destructive energy is deposited almost exclusively in the cancerous tissue. This, however, assumes that its range has been calculated correctly, which has so far been impossible to verify during irradiation. A team of researchers at the OncoRay Center Dresden, the company IBA (Ion Beam Applications) and the Helmholtz-Zentrum Dresden- Rossendorf has now solved this problem – with the help of a special device called a prompt gamma camera. "In the past, we had no means of measuring down to the millimeter how deeply protons penetrate a tumor during irradiation," says Christian Richter, head of the research group "High-Precision Radiotherapy" at OncoRay. While it is possible to pre-calculate the penetration depth of a proton beam in a homogeneous tank of water, "a patient is not a water tank, but consists of tissues of various densities, which will slow down the proton beam at different rates." This has major implications for the clinical application of proton beams. A radiation oncologist who does not know exactly whether the beam will reach the tumor, or perhaps overshoot its target, must irradiate a larger area of tissue as a precaution to ensure that all the cancer cells will be hit. "This uncertainty in range can amount to up to 10 millimeters, even more if the beam has to travel further," says Richter. This forces the doctor to treat areas of up to 10 millimeters larger than the actual tumor – and risk damaging a finger’s width of healthy tissue instead of destroying only the cancer cells. "In the past, this uncertainty in range greatly diminished the benefits of proton therapy in clinical applications." SIMULATION: Final trials using a head phantom prepare the slit camera for work with humans. Photo: OncoRay

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