Radiotherapy is sometimes used to eradicate cancer cells that might have survived surgery or chemotherapy, in breast cancer patients, for example. A side-effect of this radiation is long-term damage in the skin.
All patients, according to the US Optical Society, which is featuring the work at its Biophotonics Congress this week, experience effects including skin irritation, peeling and blistering. Patients can go on to develop permanent skin discolouration and thickening of the breast tissue months or years after treatment.
There is currently no method to predict the severity of these effects, which is why researchers at the Beckman Laser Institute are testing a new imager from start-up Modulated Imaging.
It uses eight different wavelengths of visible and near-infra-red light from LEDs and measures how much energy of each wavelength is reflected using a camera.
The metric required is how much of each wavelength is absorbed at each point on the skin – as this indicates the materials present – but variable surface scattering prevents this being inferred from the difference between light sent and light reflected.
To separate scattering and absorption effects, technique called ‘spatial frequency domain imaging’ is implemented by projecting the light in a series of patterns rather than a single wide beam using a digital micro-mirror device as a spatial modulator. It works over an area of 20x20cm at once.
“Since we use several wavelengths of light, we perform spectroscopy and obtain the content of melanin, tissue hemoglobin, in the de-oxygenated and oxygenated state, from which we can calculate the total blood volume and oxygen saturation in the tissue,” said BLI researcher Anaïs Leproux. “We measure superficially, about three to five millimeters deep.”
By precisely measure optical response throughout treatment, the hope is to better understand factors involved in skin damage, eventually predicting acute and late toxicities.
“Toxicity is basically the skin damage, a side effect from the radiation,” said Leproux. “There are a wide range of side effects that we’re observing; erythema [reddening], hyperpigmentation, discoloration, and dry or wet desquamation [peeling]. Necrosis can happen but is less common.” Thickening of the skin is a common late side effect.
“We’re hoping that we can see skin thickening in the scattering parameters we’re looking at,” she added. “We think that the radiation induces a re-modelling of the collagen in the skin, which should be seen as a change in the scattering parameter.”
Early results have identified distinctly different trends in melanin and oxygen saturation over the treatment time (see graphs).
As well as predicting damage, the group is considering the technique as an aid the development of damage-reducing lotions, and “we could optimise the current instrument in order to have shorter measurements with a cheaper device. That’s something we’ll look into,” said Leproux.