Design of Open-Source Binary Micro MLC for Small Animal Radiotherapy: An OSMD Initiative
S Prajapati1,2*, B Cox1,2, P Cadman3, R Jeraj2,T Mackie1,2, (1) Morgridge Institute for Research, Madison, WI,(2) University of Wisconsin, Madison, WI, (3) Saskatoon Cancer Centre, Saskatoon, SKWE-E-108-7 Wednesday 2:00PM - 3:50PM Room: 108
Purpose: While stationary collimators are commonly used in micro-radiation therapy (RT), binary micro-multileaf collimator (bmMLC) offers superior target conformity and beam modulation. As a part of an Open-Source Medical Devices (OSMD) initiative, the purpose of this study was to design an open-source bmMLC for micro-RT to be integrated into combined micro-PET/CT/RT system.
Methods: The collimator motion is powered by a Dagu micro-servo motor. The motor rotation pulls and rotates the custom-designed, 0.5 mm thick brass collimator-plate into open-position. A tension spring attached to the collimator-plate pushes the plate back to its default closed-position when the motor rotates back. The collimator-plates are interleaved so that consecutive plates move in opposite directions. Dosimetric tests were performed on the bmMLC using a 250 kVp X-ray beam with reference to the AAPM Report No. 72. The bmMLC was set up right in front of a Gafchromic EBT2 film for measurement. The film was placed 100 cm from X-ray source where the field size was 10 x 10 cm². Primary collimators were not used in this set up.
Results: The bmMLC prototype has been tested using ten interleaved collimator-plates which create a maximum field size of 1.5 x 2cm² at isocenter (with magnification=2). The leaf opened and closed in 0.5 seconds which is adequate for the expected low dose rate from the X-ray source. The 80% - 20% penumbra of the bmMLC in direction of leaf movement (horizontal) was 2.6 ± 0.2 mm. The vertical penumbra was 0.4 ± 0.1 mm. The X-ray transmission by bmMLC was measured to be < 0.1%. The between-leaf leakage was measured to be 6.5 ± 1%, which can be minimized by further optimizing the design and measurement set up.
Conclusion: An inexpensive, open-source, bmMLC prototype has been designed for a micro-RT system with potential for IMRT application.
Funding Support, Disclosures, and Conflict of Interest: Funding Support: Morgridge Institute for Research, Madison, WI