Purpose: In order to overcome the difficulty measuring dose with water phantom in MR-linac environment, we design a drive system with only one piezo motor that MR compatible to use in a 3D Dosimetry water phantom for the MR-linac annual quality assurance (QA) test, which had several features: 1) easy-used 2) lightweight and compact design 3) the only MR-compatible drive system which could control the 3-axes movement.
Methods: The water phantom system contained three parts: phantom box, dose measurement tools, and drive system. First, the phantom box was made of PMMA, which inner dimension was 40×20×20cm3 with an 8-mm-thick wall. Second, two different types of ion chambers and UNIDOSE universal dosimeter (PTW30013) were used for beam data collection. The ion chamber measuring depth was ranged from 18mm to 250mm, and 8mm to 250mm for cylindrical chambers and parallel plate chambers, separately. Third, the drive system consisted ceramic piezo motor, toothed wheels, arms, and another related kit is made in plastic or PMMA. The MR compatible trolley for storage and equipment transportation. To approval the whole system that home-made can use in MR based environment, this system was tested 3 times with 1.5T MR-SIM.
Results: Our results showed that the system could be operated normally in a regular MR-SIM environment without magnet field interference. With normal use, the moving speed of the phantom could reach 5 mm/ sec with the position difference confined to 1 mm and could be operated smoothly at 3 mm/sec. Safety and image interference free were validated within the environment with magnetic field less than 1.5T.
Conclusion: We build a system that can monitor the water phantom and operate the QA test with linear movement well in MR-SIM environment. With this water phantom, the duration of QA test could be shortened.
Funding Support, Disclosures, and Conflict of Interest: Funding supported in part by the Fu Jen Catholic University Hospital
MRI, Linear Accelerator, Phantoms
IM/TH- MRI in Radiation Therapy: MRI/Linear accelerator combined Quality Assurance