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One layer at a time: the use of 3D printing in the fabrication of cadmium-free electron field shaping devices

Published online by Cambridge University Press:  14 December 2020

Michael J. Moore ,
Ronald Snelgrove ,
Johnson Darko  and
Ernest K. Osei Open the ORCID record for Ernest K. Osei [Opens in a new window]
Michael J. Moore
Affiliation:
Department of Medical Physics, Grand River Regional Cancer Centre, 835 King Street West, Kitchener, Ontario, Canada, N2G 1G3
Ronald Snelgrove
Affiliation:
Department of Medical Physics, Grand River Regional Cancer Centre, 835 King Street West, Kitchener, Ontario, Canada, N2G 1G3
Johnson Darko
Affiliation:
Department of Medical Physics, Grand River Regional Cancer Centre, 835 King Street West, Kitchener, Ontario, Canada, N2G 1G3 Department of Physics and Astronomy, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada, N2L 3G1 Department of Clinical Studies, Ontario Veterinary College, University of Guelph, 50 Stone Road, Guelph, Ontario, Canada, N1G 2W1
Ernest K. Osei*
Affiliation:
Department of Medical Physics, Grand River Regional Cancer Centre, 835 King Street West, Kitchener, Ontario, Canada, N2G 1G3 Department of Physics and Astronomy, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada, N2L 3G1 Department of Clinical Studies, Ontario Veterinary College, University of Guelph, 50 Stone Road, Guelph, Ontario, Canada, N1G 2W1 Department of Systems Design Engineering, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada, N2L 3G1
*
Author for correspondence: Ernest K. Osei, Department of Medical Physics, Grand River Regional Cancer Centre, Kitchener, ON, Canada. Tel: (519) 749-4300. E-mail: [email protected]
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Abstract

Introduction:

Electron blocks are typically composed of a low melting point alloy (LMPA), which is poured into an insert frame containing a manually placed Styrofoam aperture negative used to define the desired field shape. Current implementations of the block fabrication process involve numerous steps which are subjective and prone to user error. Occasionally, bowing of the sides of the insert frame is observed, resulting in premature frame decommissioning. Recent works have investigated the feasibility of utilising 3D printing technology to replace the conventional electron block fabrication workflow; however, these approaches involved long print times, were not compatible with commonly used cadmium-free LMPAs, and did not address the problem of insert frame bowing. In this work, we sought to develop a new 3D printing technique that would remedy these issues.

Materials and Methods:

Electron cutout negatives and alignment jigs were printed using Acrylonitrile Butadiene Styrene, which does not warp at the high temperatures associated with molten cadmium-free alloys. The accuracy of the field shape produced by electron blocks fabricated using the 3D printed negatives was assessed using Gafchromic film and beam profiler measurements. As a proof-of-concept, electron blocks with off-axis apertures, as well as complex multi-aperture blocks to be used for passive electron beam intensity modulation, were also created.

Results:

Film and profiler measurements of field size were in excellent agreement with the values calculated using the Eclipse treatment planning system, showing less than a 1% difference in line profile full-width at half-maximum. The multi-aperture electron blocks produced fields with intensity modulation ≤3.2% of the theoretically predicted value. Use of the 3D printed alignment jig – which has contours designed to match those of the insert frame – was found to reduce the amount of frame bowing by factors of 1.8 and 2.1 in the lateral and superior–inferior directions, respectively.

Conclusions:

The 3D printed ABS negatives generated with our technique maintain their spatial accuracy even at the higher temperatures associated with cadmium-free LMPA. The negatives typically take between 1 and 2 hours to print and have a material cost of approximately $2 per patient.

Keywords

ABSelectron apertureelectron blockelectron cutoutradiation therapy
Type
Original Article
Information
Journal of Radiotherapy in Practice , Volume 21 , Issue 2 , June 2022 , pp. 222 - 227
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Copyright
© The Author(s), 2020. Published by Cambridge University Press

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