Taking radiotherapy soundings

Radiotherapy is an essential part of cancer treatment, but it is difficult to ascertain precisely how much radiation a tumour has received. In a bid to solve this problem, engineers at Purdue University, Indiana have invented a monitoring device that will be implanted directly into the tumour.

Babak Ziaie of the department of electrical and computer engineering explained that, currently, the only way to measure the doses is to insert a device with a wire into the tumour, which is painful. ‘By the end of the summer, we will have a prototype that can be put directly into the tumour with a hypodermic needle.’

The device is extremely simple. It has no battery, and contains just a coil and a capacitor. It works on the same principle as the electret microphone, where a membrane moves in response to soundwaves, increasing and decreasing capacitance in the gap between the membrane and a metal plate.

‘The capacitance changes as a function of radiation,’ Ziaie explained. ‘Just like a radio, where the station changes with the frequency, as the radiation changes so does the frequency. This can be read from outside the body using a handheld monitoring device.’

The current prototype is about the size of a 5p piece, but the version that will be ready later this year will be the size of a grain of rice. It will be encased in a glass capsule, and as it is biocompatible there will be no need to remove it after treatment has finished.

‘We are also working on a future generation that will enable a tumour to be tracked,’ said Ziaie. ‘As the patient moves around or lies down, the tumour moves, and it is helpful to know precisely where it is while therapy is carried out.