Tokyo, Japan – A team led by researchers from Tokyo Metropolitan University, in collaboration with Tohoku University and Orbray Co., Ltd., using heteroepitaxial diamond materials developed by Orbray, have shown that lab-grown diamonds might realize a radiation dosimeter compatible with both medical diagnosis and radiation therapy. They demonstrated that a diamond-based dosimeter could accurately measure doses in the same energy range as diagnostic X-rays, with far better sensitivity per volume than conventional detectors. Using the same device for dosimetry during both diagnosis and therapies could enable improved consistency.
Accurate measurement of radiation dose is crucially important in clinical workplaces. The standard option for dosimetry (dose measurement) is the air-based ionization chamber, where radiation passing through a volume of air produces a measurable current. However, a major challenge lies in the range of doses that dosimeters need to handle. For example, diagnostic X-rays involve doses which are much lower than in radiation treatment. Air-based ionization chambers for the former might require a significant volume of air, making detectors cumbersome, with little scope for mapping out how dose changes depending on detector position. Practically, sensitivity is prohibitively low at very low dose levels.
Now, a team of researchers led by Professor Kiyomitsu Shinsho from Tokyo Metropolitan University have challenged this paradigm by using an entirely new material for their ionization chambers. Instead of air, they turned to diamonds grown in the lab using a method known as heteroepitaxy. They used cutting edge technology to lay down atoms layer by layer and grow lab-grown diamonds on an electrode. With this new detector, the team performed systematic experiments on how the diamond might be used as an ionization chamber at the kinds of doses seen in X-ray diagnosis. The chamber, measuring 4 by 4 by 0.5 mm, has a volume around 1250 times smaller than typical air ionization chambers, but a sensitivity per volume which was 13,500 times higher when a relatively low voltage of -100V was put across it. They demonstrated excellent linearity of response with dosage, with very little dependence on the energy of the X-rays. Crucially, its success at the low energies used in diagnostic devices suggests that it might easily deal with the higher doses seen in therapies: this paves the way for the development of a dosimeter that can be used in both diagnosis and radiation therapies. Diamond is also made of carbon, making it an excellent analogue for human tissue.
This is a big step forward for dosimetry for many reasons. The compactness of the device makes it applicable virtually anywhere, from personal dosimetry, real-time measurements during treatments to environmental monitoring. It is compact enough to produce an array, like the sensor array on a camera, which could map the change in dose over some area. Sensitivity to low doses could also revolutionize our understanding of the effects of low radiation exposure on the human body, a crucial component of radiological research. Most importantly, it opens the door to achieving sorely needed consistency to measurements of radiation dose. The potential use of the same device in entirely different contexts would make dose comparisons scientifically sound and fair. The team's success promises a big leap forward for both medical workplaces and our understanding of radiation in the environment.
This work was supported by a joint research fund, Grant/Award Number GG5-1170, by Tokyo Metropolitan University, Tohoku University, and Orbray Co., Ltd.
