Room: AAPM ePoster Library
Purpose: C-11, N-13, O-15 are short half-life PET isotopes that are only viable through on-site production. Traditionally, cyclotrons can generate these isotopes with large beam currents of energetic ions smashing into suitable targets. Unfortunately cyclotrons are often large and expensive to build. We propose to use a pulsed line ion accelerating (PLIA) as a cheaper and more compact alternative that operates at a high-repetition rate to produce enough beam current.
Methods: PLIA’s principle is similar to a coaxial transmission line with a hollow center conductor where particles propagate. Applying a steep voltage ramp on the line generates a strong accelerating electric field that propagates in the hollow space. A spiral generator produces a fast, high-voltage ramp that maximizes the accelerating gradient. The generator is equivalent to a long capacitor rolled around a mandrel and terminated by a solid-state switch operating at 500Hz. The rolled design allows the output to be 10 to 50 times the charging voltage.
Results: The compact design that associates energy storage and pulse shaping in one structure allows extremely fast switching of pulse polarity over voltage amplitudes of 500-1000 kV. The large voltage gain signifies that the spiral generator stores and mostly operates with voltages of 10-20kV, allowing the use of high repetition rate solid-state switches and significantly reducing the chances of corona and electrical breakdown. When coupled to PLIA, ramps as short as 40ns were observed corresponding to accelerating gradients above 3MV/m. Therefore a 3m PLIA operating at 500Hz would produce an average current of 10uA, enough to generate doses of 100s of mCi for imaging.
Conclusion: The use of a high repetition rate generator with high output voltage but significantly lower input voltage allows the safe operation of a PLIA structure with beam currents and energies suitable for short half-life PET isotope production.