Applied Physics Seminar: "Can listening to x-ray radiation Improve cancer targeting?"

Radiotherapy can be a highly effective treatment for many types of cancers. A major impediment to achieving its full curative promise is the current delivery process, where typically the originally planned tumor area is exposed to a fixed pattern of ionizing radiation over time irrespective of target deformations, organ motion, or function. To avoid misses, geometric uncertainties in this feedforward process are dealt with by increasing the planning margin around the tumor, but of necessity result in unnecessary exposure of uninvolved tissue which can lead to debilitating toxicities. We hypothesize that the unwanted radiation dose to normal tissues could be significantly reduced by using a feedback system that would “monitor” the shape and location of the tumor as well as the location and intensity of the irradiated dose during delivery. This framework would require the unique ability to simultaneously image the absorbed dose and the targeted tumor anatomy during radiation delivery. A known phenomenon in radiation physics is the generation of acoustic waves due to thermal expansion of a substance following the absorption of penetrating radiation. That signal exists “for free” in real time as a consequence of the treatment beam. In this presentation, we review the underlying physics of the radiation acoustics phenomenon and its characteristics, highlight recent developments for its measurements, and discuss its current potentials and challenges for online cancer tracking and targeting.