A Live Image During Tumor Irradiation

Ionoacoustics enables a precise real-time imaging of the position in tissue (pink) where the irradiation releases its biggest effect (displayed in purple) (Source: S. Kellnberger)

Ionoacoustics enables a precise real-time imaging of the position in tissue (pink) where the irradiation releases its biggest effect (displayed in purple) (Source: S. Kellnberger)

In future, the irra­diation of tumors with protons could become more precise. Medical physicists from the Munich-Centre for Advanced Pho­tonics MAP at the Ludwig-Maxi­milians-Uni­versität LMU, together with physicists from the Technical University TUM, the Helmholtz Zentrum München HMGU and the Universität der Bundes­wehr München UniBWM have combined con­ventional ultra­sound techno­logy with proton irra­diation of a tumor. Using iono­acoustic technology they developed, they are able to observe the action of proton beams in real time via ultra­sound.

A large number of tumors can be treated with ra­diation consisting of protons, which attack and destroy the cancer cells of the tumor. However, it is crucial that the protons attack and kill only cancerous cells while sparing the sur­rounding healthy tissue. Doctors must therefore direct the energy of the protons precisely within the tumor in order to have maximum impact on the tumor cells. In clinical appli­cations, it is therefore impor­tant to know where the radiation from protons unleashes its maximum effect. In the human body, this is precisely where protons get stopped. This point of maximum dose delivery is known as the Bragg peak and should only occur within the tumor.

The medical physi­cists have now developed a method with which they can check where ion radiation deposits dose in a tumor during ir­radiation. They combined conventional ultrasound measure­ments with the simul­taneous measure­ment of the ultra­sonic signal caused by the proton irra­diation. They first succeeded in making a beam of protons visible in tissue with an ultrasound image of this piece of tissue during a pre­clinical experiment. Using their own developed “iono­acoustic” techno­logy, they are now able to track where ion radiation reaches its greatest effec­tiveness in the body – in real time, and in three dimensions. The resear­chers were thus able to determine the accuracy of the proton Bragg peak to within less than a milli­meter. In addition, using controlled illu­mination with laser light, they were able to simul­taneously measure an opto­acoustic image of the irra­diated tissue.

In order to adapt iono­acoustics for clinical practice, the physicists want to modify this ultra­sound techno­logy so that signals can be measured even at conven­tionally used levels of radiation at thera­peutic energies. At present, proton beams are still produced using large and expensive acce­lerator faci­lities. But new laser techno­logies being developed at the Munich-Centre for Advanced Photonics and its laser research center, the Centre for Advanced Laser Appli­cations (CALA), promise cheaper – and possibly energe­tically better adapted – proton radiation for medical use. For laser-driven beam pro­duction, iono­acoustics promises to be a parti­cularly suitable and highly accu­rate mea­surement method to make proton therapy more targeted and thus poten­tially more bene­ficial to patients in future. (Source: LMU)

Reference: S. Kellnberger et al.: Ionoacoustic tomography of the proton Bragg peak in combination with ultrasound and optoacoustic imaging, Sci. Rep. 6, 29305 (2016); DOI: 10.1038/srep29305

Links: Inst. for Biological and Medical Imaging, Technische Universität München and Helmholtz Zentrum München, Neuherberg, Germany • Dept. for Medical Physics, Ludwig-Maximilians-Universität München, Garching, Germany

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