Abstract
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.
Highlights
Many isotopes for diagnostic and therapeutic applications can be produced on a medical cyclotron.To maximize the production of medical radioisotopes, the system’s parameters must be understood.the shape, trajectory, and the location of the proton beam relative to the production target must be quantified to optimize production yields
While the signal is lower than in the larger Ce-doped fiber when the 18 O gas target is irradiated, it does not scale with the cross-sectional area of the fiber by a factor of nine but only drops by a factor of four
It should be noted that the two Ce-doped fibers were of different lengths, with the larger fiber being 2.6 times longer, which may account for the difference in signal response
Summary
To maximize the production of medical radioisotopes, the system’s parameters must be understood. The shape, trajectory, and the location of the proton beam relative to the production target must be quantified to optimize production yields. For low energy cyclotrons, no techniques are available that allow for real-time monitoring of proton beams that enable operators to evaluate the beam position and angle relative to the target being irradiated, or the beam shape in real time and in situ. High energy particle beams can be profiled in real time by intercepting the beam with sensors. Low energy cyclotrons cannot be profiled in this manner as these materials would absorb a large fraction of the beam’s energy; reducing the cyclotron’s production efficiency [1]
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