Image: Ultrahigh dose proton RT can deliver an entire radiation dose in a second (Photo courtesy of Getty Images)
A new study details how proton radiation can be used to theoretically give a cancer patient their entire course of radiotherapy (RT) in one rapid treatment.
Developed by researchers at the University of Pennsylvania (Penn; Philadelphia, USA), ultrahigh-dose-rate (FLASH) proton RT can deliver an entire radiation dose in an extremely short time span via double scattered protons and computed tomography (CT) guidance. Using a mouse model of pancreatic tumors, the effect of FLASH RT versus standard dose rate RT on both tumors and normal tissue was measured using pancreatic flank tumors in syngeneic C57BL/6J mice, with analysis of fibrosis and stem cell repopulation in the small intestine after abdominal irradiation.
The results showed that whole abdominal FLASH proton RT at 15 Gy significantly reduced the loss of proliferating cells in intestinal crypts, compared with standard proton RT. Studies with local intestinal irradiation at 18 Gy revealed a reduction to near baseline levels of intestinal fibrosis, compared with standard proton RT. The researchers also found that FLASH proton RT spared healthy tissue. The study was published in the February 2020 issue of the International Journal of Radiation Oncology, Biology, and Physics.
“We've been able to develop specialized systems to generate FLASH doses, demonstrate that we can control the proton beam, and perform a large number of experiments to help us understand the implications of FLASH radiation that we simply could not have done with a more traditional research setup,” said co-senior author James Metz, MD, director of the Penn Roberts Proton Therapy Center. “Using this system, we found that FLASH proton RT decreases acute cell loss and late fibrosis after whole-abdomen and focal intestinal RT, whereas tumor growth inhibition is preserved between the two modalities.”
FLASH RT involves the ultra-fast delivery of radiation at dose rates several orders of magnitude greater than those currently in routine clinical practice. In order to eradicate tumors, all cancerous cells must be killed, with normal tissue being spared from radiation damage as much as possible. Ultra-fast dose rates allow normal tissue tolerance levels to be exceeded, at least in animal models, with a greater probability of tumor control and little normal tissue damage. One mechanism suggested is that FLASH consumes all available oxygen and liberates significantly more electrons, resulting in many more ionization events than at conventional dose rates.
University of Pennsylvania