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Featured Application: Use of fiber optics to monitor a target on a medical cyclotron. Many medical isotopes can be produced on a small cyclotron. The alignment and profiles of low-energy proton beams from cyclotrons used for medical radioisotope production, such as the TR13 cyclotron at TRIUMF, Canada, cannot be directly quantified during dose delivery with simultaneous constant feedback and sharp spatial resolutions. Doped silica fibers are a potential solution that has been tested at TRIUMF. To measure the effects of irradiation inside an isotope production target, we attached fibers to the outside of an 18O gas target and measured the light output during irradiation. Different dopants, fiber diameters, and target materials were investigated. It was found that 200 µm diameter Ce- and B-doped fibers produce signals linearly proportional to the beam current. This only deviated when the target was moved such that the beam was steered into the target wall, increasing the production of prompt radiation and causing the beam current to decrease but the fiber signal to increase. With the technique described here, the beam can be monitored on the target, including its steering and its overall alignment with the target. [ABSTRACT FROM AUTHOR]

The TRIUMF particle accelerator center in Vancouver, British Columbia, Canada houses a proton therapy beam line formerly used for the treatment of ocular cancer. This existing Proton Therapy Research Centre (PTRC) was upgraded to deliver protons at ultra-high dose rates which would be required for FLASH radiotherapy treatments. A peak dose rate of 110 Gy/s over an area of 20 mm 2 was delivered at a beam energy of 21 MeV. This was achieved by degrading the cyclotron extracted beam energy of 70 MeV using polymethyl methacrylate (PMMA) plates. In addition, a fast, versatile and reliable method for producing static ridge filters has been developed to spread the proton beam to the entirety of the target axially (i.e., in depth). FLASH dose rates were maintained with a spread-out Bragg peak of 0.5 cm. [ABSTRACT FROM AUTHOR]