Proton beam therapy is a novel radiation treatment which offers superior dose localization. This is due to the “Bragg Peak” effect of protons, in which they tend to group together near their range in the material. This presents a unique opportunity for fine-tuned treatment planning but requires sensitive calibration of delivered dose. An evacuated ion chamber is the preferred method of dose assessment but this involves expensive investment, operation, and upkeep; this is outside of the lost time due to breaking workflow to setup and configure a calibration.
The “Poor Man’s Faraday Cup” (Portable Faraday Cup) was originally proposed by B. Gottschalk, constructed from a conducting metal block coated with an electrically insulating film. The voltage and current across the conductor (e.g. copper) is continuously measured as the block is bombarded with positively charged protons. The thin insulator is used to absorb stray and backscattered electrons and reduce artificial current gain. Prototypes with variations of these specs have been evaluated for resulting current gain using the MCNP5 and Geant4 particle transport codes. It was found that current gain increases with proton energy, and as expected the model without an insulating Kapton layer resulted in a higher gain than those with different thicknesses of Kapton. The energy dependence has been linked to the loss of deflected low-energy protons barely penetrating the conductor. These results have been presented at the meeting of the American Association of Physicists in Medicine.
📰 Publications
- S. Marshall, A. Hodgdon, B. Currier. Computational Evaluation of Proton Induced Gain in a Portable Faraday Cup. 11th Annual Graduate Research Innovation Exchange. 3 Feb 2016.
- S. Marshall, A. Hodgdon, B. Currier. Computational Evaluation of Proton Induced Gain in a Portable Faraday Cup. 57th Annual Meeting of the American Association of Physicists in Medicine. 14 Jul 2015.