Rather than relying on computer models or guesswork, doctors may soon be able to monitor the efficacy of radiotherapy against cancer using microbubbles that stick to the surface of tumours.

Researchers at the University of Leuven, Belgium, have developed a system using gas-filled microbubbles and ultrasonic sound waves to determine if radiation has reached targeted areas of the body, which could help reduce damage to healthy tissue around tumours. Microbubbles work by resonating in an ultrasound beam, contracting and expanding in response to pressure from sound waves, allowing them to be differentiated from other tissue. 

The technique developed by researchers at the University of Leuven starts with the injection of gas-filled microbubbles into the bloodstream, where the tiny bubbles seek out and bind to the surface of tumours. Ultrasonic sound waves are sent to the microbubbles, which makes them vibrate at their natural frequency. The vibrations are measured before and after radiotherapy, and if the radiation has reached the targeted area, the microbubbles will have become stiffer and thus vibrate at a higher frequency. The change in frequency and attenuation is a measure of the radiation dose.

Researchers at the university have already received a patent for the technique, and tested it in lab experiments and with mice, but say more research is needed before testing the microbubble method in humans.