Researchers at the University of Pennsylvania have demonstrated that a new approach to delivering radiation could one day mean that cancer patients will be able to receive their entire course of radiotherapy within less than a second as opposed to several weeks.
As recently reported in the journal International Journal of Radiation Oncology, Biology, and Physics, James Metz and colleagues used proton radiation to generate a radiation dosage that, technically, would be enough to give a patient their entire course of radiotherapy all in one go.
Recent studies have suggested that, compared with conventional-dose rate electron radiotherapy (RT), a technique called FLASH electron RT decreases normal tissue damage, while maintaining tumor response.
However, “proton radiation therapy (PRT) can improve spatial dose delivery compared with photons or electrons,” write Metz and team. “Here, we describe a novel RT apparatus that delivers FLASH proton RT (PRT) using double scattered protons with computed tomography guidance and provide the first report of proton FLASH RT-mediated normal tissue radioprotection.”
The feasibility of using protons rather than electrons
Using a mouse model of pancreatic tumors, the team demonstrated FLASH PRT inhibited tumor growth as effectively as traditional photon radiation, whilst sparing healthy tissue.
This is the first time anyone has published findings that demonstrate the feasibility of using protons - rather than electrons - to generate FLASH doses, with an accelerator currently used for clinical treatments,"
Metz, University’s Roberts Proton Therapy Center
Other research groups have managed to deliver similar radiation doses using electrons, notes Metz, but this does not penetrate deep enough to target internal tumors. Other research teams have also tried to deliver radiation using conventional photons, but todays devices cannot produce the required dosage.
Now, the study by Metz and the team shows that with technical modifications, proton accelerators can generate the dosage needed to exert the desired biological effects. Since standard detectors are rapidly saturated by high levels of radiation, Metz and team developed apparatus that would measure radiation doses quickly and effectively:
“We have designed and dosimetrically validated a FLASH-PRT system with accurate control of beam flux on a millisecond time scale and online monitoring of the integral and dose delivery time structure.”
The Roberts Proton Therapy Center
The Roberts Proton Therapy Center is one of the few facilities in the world to include a research room dedicated to running experiments such as these, where photon and proton radiation techniques can be tested alongside one another in close vicinity to the clinic. Metz says it was this unique arrangement that enabled the team to perform their new FLASH experiments.
We've been able to develop specialized systems in the research room 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. Using this system, we found that FLASH-PRT decreases acute cell loss and late fibrosis after whole-abdomen and focal intestinal RT, whereas tumor growth inhibition is preserved between the 2 modalities.”
Metz, University's Roberts Proton Therapy Center
Researchers have said they are already starting to build on the development to see how it could be used in clinical trials, including seeing what would be needed to translate it from the research room to the clinic. Future steps also include plans to design a FLASH delivery system for humans.
Design, Implementation, and in Vivo Validation of a Novel Proton FLASH Radiation Therapy System, Diffenderfer, Eric S. et al.
International Journal of Radiation Oncology, Biology, Physics, Volume 106, Issue 2, 440 - 448. DOI: https://doi.org/10.1016/j.ijrobp.2019.10.049