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, has shown that lab-grown diamonds can realize a radiation dosimeter compatible with both medical diagnosis and radiation therapy. They showed that a diamond-based dosimeter could accurately measure doses in the same energy range as diagnostic X-rays, with much better sensitivity per volume than conventional detectors. Using the same device for dosimetry both at diagnosis and during treatments could allow for improved consistency.
Accurate measurement of radiation dose is vital in clinical workplaces. The standard choice 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 must handle. For example, diagnostic x-rays involve much lower doses than in radiation therapy. Air-based ionization chambers for the former may require a significant volume of air, making detectors unwieldy, with little scope for mapping how dose changes with detector position. In practice, the sensitivity is prohibitively low at very low dose levels.
Now, a team of researchers led by Professor Kiyomitsu Shinsho from Tokyo Metropolitan University has challenged this paradigm by using an entirely new material for their ionization chambers. Instead of air, they turned to lab-grown diamonds using a method known as heteroepitaxy. They used state-of-the-art technology to place atoms layer by layer and grow lab-grown diamonds on an electrode. With this new detector, the team conducted systematic experiments on how diamond could be used as an ionization chamber at the kinds of doses seen in x-ray diagnostics. The chamber, measuring 4 by 4 by 0.5 mm, has a volume of about 1250 times smaller than standard air ionization chambers, but the sensitivity per volume was 13,500 times higher when applying a relatively low voltage of -100 V. They showed excellent linearity of response with dosage, with very little dependence on X-ray energy. Importantly, its success at the low energies used in diagnostic devices suggests that it could easily cope 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 treatments. Diamond is also made of carbon, making it an excellent analog for human tissue.
This is a big step forward for dosimetry for several reasons. The device’s compact design makes it applicable almost anywhere, from personal dosimetry, real-time measurements during treatments to environmental monitoring. It is compact enough to produce an array, like the sensor array in a camera, that could map the change in dose in an area. Low-dose sensitivity could also revolutionize our understanding of the effects of low radiation exposure on the human body, a critical component of radiological research. More importantly, it opens the door to achieving much-needed consistency in radiation dose measurements. The potential use of the same device in completely different settings would make dose comparisons scientifically sound and fair. The team’s success promises a great leap forward for both the medical workplace and our understanding of radiation in the environment.
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