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An Open Source Motorized Water Phantom for MR-Linac Commissioning

C V Guthier*, E Huynh, C L Williams, Dana-Farber/Brigham and Women's Cancer Center, Harvard Medical School, Boston, MA


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

Room: AAPM ePoster Library

Purpose: MRI-guided linear accelerators are an emerging modality that present unique challenges for system commissioning. The high magnetic field environment makes many traditional quality assurance devices non-functional or unsafe. Motorized scanning water phantoms are widely used in accelerator commissioning, but current motorized scanning water phantoms are not safe to use in an MR-Linac, so measurements must be taken with a manually operated water tank. This study presents the development of an open source MRI-safe motorized water phantom used for commissioning.

Methods: An existing 1-dimensional manual scanning water tank (MedTec) was modified with a customized motor unit. The motor unit was based on an ultrasonic motor and encoder unit (USR30-E3N motor, and D6060E driver unit, Shinsei Corporation, Tokyo, Japan). A control unit was built using an Arduino-compatible microcontroller development board with a liquid crystal display. 3D printed holders and gears were designed to mount the motor to the translational screw of the water tank with no modifications to the tank hardware. Translation was manually verified using the water tank rotation counter. Hardware specifications, 3D printable files, and source code for the controller are publicly available on Github. For validation, percent-depth-dose curves (PDDs) were obtained with the manual water phantom and were compared against the motorized version.

Results: Material costs for the system was approximately $1500. PDDs taken with the motorized water phantom were within (0.47±0.02)% of the manual phantom measurements beyond dmax. The time per each measurement depth for the manual and for the motorized phantoms were (3.0±1.0)minutes and (1.4±0.5) minutes, respectively. The total time saving during commissioning measurements of 341 PDD points was estimated to be 22.7hours.

Conclusion: The presented motorized phantom significantly simplified and accelerated the MRIdian commissioning process. The open-source nature of the project provides centers commissioning MR linear accelerators with a cost-effective and time saving tool.


Not Applicable / None Entered.


TH- External Beam- Photons: Quality Assurance - Linear accelerator

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