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The Use of 3D Printing in the Fabrication of Cadmium-Free Electron Cutout Blocks

M.J. Moore1*, R Snelgrove1, O Masella1,2, J Darko1,2,3, E.K. Osei1,2,3, (1) Grand River Regional Cancer Centre, Kitchener, ON, CA, (2) University of Waterloo, Waterloo, ON, CA (3) University of Guelph, Guelph, ON, CA


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: Electron cutout blocks are formed by pouring molten alloy into an insert frame containing a manually placed Styrofoam aperture negative. This process involves steps which are inherently subjective and prone to user error. Furthermore, significant bowing of the insert frame is sometimes observed, causing the block to be unsuitable for therapeutic use. In this work, we present an electron block fabrication approach which utilizes 3D printing technology to overcome several of these challenges.

Methods: Plans containing electron block apertures were exported from Eclipse v13.6. A custom Python GUI was developed and used for importing files and generating 3D printable models of the plan aperture negative. Jigs for the insert frames were designed to facilitate positioning of the negative and reduce frame bowing. All components were sliced using Simplify3D, then printed with a Raise3D N2 3D printer using Acrylonitrile Butadiene Styrene (ABS) filament.

Results: By using ABS printer filament, warping of the 3D printed parts at the high temperatures associated with molten cadmium-free alloys was prevented. Gafchromic film measurements demonstrated that fields produced by blocks generated with the 3D printing technique had less than 1% difference in field full-width at half-maximum compared to the corresponding Eclipse plans. Versatility of the technique was demonstrated through the production of both off-axis and multi-aperture electron blocks. Finally, the 3D printed jigs were found to reduce the amount of frame bowing by an approximate factor of 2 in both lateral and superior-inferior directions.

Conclusion: Our technique produces electron blocks with fields having high geometrical accuracy, reduces insert frame bowing, and can produce complex electron blocks without the need for specialized machine shop equipment. The printed negatives require 1–2 hours of printing time and cost approximately $2 per patient, while the jigs cost approximately $10 and can be used to produce multiple blocks before replacement.

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