WE‐E‐108‐07: Design of Open‐Source Binary Micro MLC for Small Animal Radiotherapy: An OSMD Initiative

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 × 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 × 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: Morgridge Institute for Research, Madison, WI.