Side effects of radiation therapy can only be minimized by carefully regulating radiation doses, but knowing exactly how much radiation enters a body is not easy to assess. Normally, treatment is planned according to computer simulations generated by CT scans, and, at select points during a course of treatment, a patient can also have a detector inserted into them to estimate the amount of incident radiation. Such methods are not foolproof, however: a patient could lose weight, for instance, leading to a relatively high dose.

One new approach to measuring radiation dose is to make use of Cerenkov radiation, which is emitted when electrons and other charged particles travel through a dielectric medium faster than light would travel. Cerenkov radiation is potentially visible as flashes of light during radiation therapy as the radiation penetrates the tissue, and is in most cases proportional to the dose.

Earlier this year, Brian Pogue at Dartmouth College in Hanover, NH, and others successfully demonstrated that Cerenkov radiation could be used to estimate the radiation being received during therapy on a live dog that was suffering from an oral sarcoma tumour (see Cerenkov light tracks radiation dose).

Now Pogue's group has gone one step further by testing Cerenkoscopy on a human patient who was suffering from a breast tumour. The researchers employed the same apparatus, incorporating a gated CCTV camera about five metres from the patient that continuously acquired Cerenkov images (at 2.8 frames/s) whenever radiation pulses were delivered. By also capturing the total light when the radiation pulses were not being delivered, the system could subtract the ambient light and leave for inspection only the bursts of Cerenkov radiation. The researchers captured the Cerenkov radiation emitted by the patient's breast tissue 10 times for each of 10 different radiotherapy sessions.

Pogue and colleagues found that they could see the radiation beam incident on the breast tissue clearly, with shape and intensity related to the dose. The images were repeatable, they say, indicating that the imaging is stable. But the real benefit of the technique was that changes in the shape of the radiation beam could be imaged in real time – a feature that makes Cerenkoscopy stand out from other dosimetry methods.

"The strongest benefits might be in the ability for real-time feedback," says Pogue. "As far as we are aware, this is the only way to directly visualize radiation dose incident upon tissue, and would allow radiation therapists to actually see what they are doing when they press the button to deliver radiation dose."

Pogue says that the team has now finished imaging 12 further patients, and will be publishing those results soon. "All these results were reported on one subject, so need confirmation," he adds.

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