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Spreading Tattoo Ink Reveals Radiation-Induced Necrosis

Physics World

April 14, 2020

"Functional imaging modalities can characterize responses of the tumour microenvironment. But common techniques, such as PET or diffusion-weighted MRI, require a separate scheduled exam. Researchers from Dartmouth College’s Thayer School of Engineering have now proposed a way to image the tumour microenvironment during radiotherapy without interrupting the clinical workflow, using Cherenkov-excited luminescence imaging (CELI). They achieve this by employing CELI to track the spread of a phosphorescent tattoo ink," according to a Physics World article. ...

..."'In the last few years, our lab has done a great deal of radiotherapy research focused on imaging the radiation beam delivered to the patient in real time using time-gated Cherenkov imaging,' says first author Jennifer Soter, a PhD student in Brian Pogue’s research group. 'We were prompted to expand on this technology further and explore additional applications in cancer treatment. In the case of tumour progression in radiotherapy, there’s really no feasible method that enables daily imaging of tumours clinically.'

"Soter and colleagues used a mouse model to evaluate whether CELI can directly track subtle changes in the tumour microenvironmental in response to radiation therapy. On day zero, they injected tattoo ink into the centre of tumours in 20 mice. They then delivered a 1.4 Gy treatment fraction to all mice, using 6 MV X-ray beams from a clinical linac, and performed a baseline CELI session to measure the initial spread of the ink.

"The researchers used an intensified CMOS camera to detect visible phosphorescence from the ink. The camera was time-gated with the linac pulses, such that it only recorded the delayed phosphorescence signals emitted between each radiation pulse. Immediately after the first CELI session, they delivered an additional 12 Gy dose to 15 mice, while nine untreated controls received no additional radiation. One to six days later, they delivered a second 1.4 Gy to each mouse and performed the final CELI session.

"By comparing images acquired immediately after injection with the final diffusive ink spread, the researchers could determine the tumour response. 'Cell death via apoptosis and necrosis can lead to significant sections of the tumour decreasing, resulting in tissue clearance, which is well known from diffusion MRI,' explains Soter. 'The ink is a simple label that also diffuses from within the tumour as the pressure decreases.'"

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