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Research Papers

Design of an Open-Source Binary Micromultileaf Collimator for a Small Animal Microradiotherapy System

[+] Author and Article Information
Surendra Prajapati

Department of Medical Physics,
University of Wisconsin-Madison,
1111 Highland Avenue, Room 1005,
Madison, WI 53705;
Morgridge Institute for Research,
330 North Orchard Street,
Madison, WI 53715
e-mail: prajapatisurendra@gmail.com

Benjamin Cox

Morgridge Institute for Research,
330 North Orchard Street,
Madison, WI 53715;
Department of Medical Physics,
University of Wisconsin-Madison,
1111 Highland Avenue, Room 1005,
Madison, WI 53705
e-mail: bcox1@wisc.edu

Robert Swader

Morgridge Institute for Research,
330 North Orchard Street,
Madison, WI 53715
e-mail: RSwader@morgridge.org

George Petry

Morgridge Institute for Research,
330 North Orchard Street,
Madison, WI 53715
e-mail: GPetry@morgridge.org

Kevin W. Eliceiri

Morgridge Institute for Research,
330 North Orchard Street,
Madison, WI 53715;
Department of Medical Physics,
University of Wisconsin-Madison,
1111 Highland Avenue, Room 1005,
Madison, WI 53705
e-mail: eliceiri@wisc.edu

Robert Jeraj

Department of Medical Physics,
University of Wisconsin-Madison,
1111 Highland Avenue, Room 1005,
Madison, WI 53705
e-mail: rjeraj@wisc.edu

Thomas R. Mackie

Department of Medical Physics,
University of Wisconsin-Madison,
1111 Highland Avenue, Room 1005,
Madison, WI 53705;
Morgridge Institute for Research,
330 North Orchard Street,
Madison, WI 53715
e-mail: trmackie@wisc.edu

1Corresponding author.

Manuscript received February 12, 2017; final manuscript received September 11, 2017; published online October 16, 2017. Assoc. Editor: Chris Rylander.

J. Med. Devices 11(4), 041007 (Oct 16, 2017) (10 pages) Paper No: MED-17-1034; doi: 10.1115/1.4038017 History: Received February 12, 2017; Revised September 11, 2017

Intensity modulated radiation therapy (IMRT) is performed on a regular basis in the clinic to create complex radiation fields to treat cancer, but it has not been implemented in microradiotherapy (mRT) for preclinical systems. A multileaf collimator (MLC) is an integral part of a radiotherapy system that allows IMRT application. Presented here is the development of a key component of an open source mRT system for preclinical research. We have designed and fabricated a binary micro multileaf collimator (bmMLC) for mRT that can provide 1 mm or better resolution at isocenter and attenuate over 98% of a 250 kVp X-ray beam. This is the smallest collimator system designed for RT systems, with 20 brass leaves, each 0.5 mm thick, creating a physical field opening of 1 cm × 1 cm. The mode of actuation for the leaves was rotational, rather than linear, which is typical in larger clinical RT systems. The design presented here met the identified design requirements and represents a rigorous design process, during which several less successful designs were investigated and eventually discarded. After the fabrication of the design, dosimetric characteristics were tested and requirements were met. The final bmMLC designs and technical documents are made available as open-source.

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Figures

Grahic Jump Location
Fig. 1

3D rendering of the design of a SAITS system showing the bmMLC assembly

Grahic Jump Location
Fig. 2

3D rendering of the design of the bmMLC assembly showing the motion mechanism, (a) base support plate design with motor housing and leaf stops, (b) 3D view of the one side of the bmMLC assembly showing different parts and X-ray beam path, and (c) Front view of the leaves in both the open (left) and closed (right) configurations with the beam path labeled in each case

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Fig. 3

3D rendering of the design of the bmMLC assembly showing both halves of the assembly bolted together but without showing the primary collimator, (a) 3D side view of the bmMLC assembly and (b) Top view of the bmMLC assembly

Grahic Jump Location
Fig. 4

3D rendering of the design of the bmMLC assembly with both halves bolted together and with the primary collimator mounted on top providing a 0.95 cm × 0.95 cm opening, (a) top view of the complete assembly showing the primary lead collimator covered by the aluminum collimator and (b) isomeric view of the complete assembly

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Fig. 5

(a) Photograph of 10 leaf bmMLC subassembly of bmMLC design connected to Arduino microcontroller where each leaf was connected to corresponding motor via the two SS wires, (b) Single collimator leaves showing the curved bottoms and the positions of the slits where the SS wires were glued with DP420. The other end of each SS wire was screwed into two sides of the spool attached to the corresponding motor, (c) Close-up view of the leaves from panel “a” with the wire connections and beam path labeled. The wire connections do not interfere with the beam path, and (d) A complete bmMLC assembly (front view) showing the primary collimator with the central opening of 0.95 cm × 0.95 cm.

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Fig. 6

(a) Blue Water homogeneous stack phantom and (b) showing the positions of films in between slabs of Blue Water; the last block on the right was placed for backscatter

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Fig. 7

Schematics of in-phantom bmMLC assembly dosimetry measurement with the end of bmMLC leaves at position 90 cm and phantom surface positioned at 10 cm SSD

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Fig. 8

bmMLC profile images measured in-phantom with bmMLC assembly positioned at 90 cm SSD and phantom positioned at 100 cm SSD, (a) all leaves open (at five depths), (b) all leaves closed (bmMLC position between the dash-dotted lines), (c) all even-numbered leaves open, (d) L1-L10 closed, (e) L10 closed, and (f) L10 open

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