Author: Paul J. Black, Jordan B Lunsford, James D. Ververs, India Wood 👨🔬
Affiliation: Atrium Health Wake Forest Baptist, Wake Forest University School of Medicine, Wake Forest School of Medicine 🌍
Purpose:
To develop a 3D-printed modular CT simulator phantom that allows the assessment of all AAPM TG-66 recommended monthly quality assurance (QA) tests.
Methods:
A modular CT simulator monthly QA phantom was designed using AutoFusion360 software (AutoDesk, Inc.) and printed on a Bambu X1C 3D printer (Bambulab USA, Inc.). The 16x16x17 cm3 phantom base incorporates laser alignment markings, a ruler to assess laser and table indexing, and four slots for additional test modules. Cylindrical plugs of varying combinations of PLA and StoneFil Granite (SFG) filament were printed to establish the correlation of Hounsfield Units (HU) with infill density (%). Plugs with infill densities equivalent to bone and Gammex (Sun Nuclear Corp.) LN-300 Lung, LN-450 Lung, Breast, and Brain plugs were printed for testing CT number accuracy. A solid water-equivalent module was printed to test uniformity. The 16 x 16 cm2 front and rear face of the phantom allow spatial integrity assessment.
Results:
A linear correlation was found between HU and infill density for both PLA (R2=0.9997) and SFG (R2=0.9958). HU values for the uniformity slab at five regions of interest (ROIs) ranged from -2.37 to +1.72, with an average deviation of 1.63 HU from center. The agreement between PLA-printed plug HU values and Gammex plugs ranged 0-9 HU. The bone plug (printed with SFG) differed from the Gammex B200 bone plug by 83 HU. Spatial accuracy dimensions and laser alignment markings agreed with expected values.
Conclusion:
This 3D-printed QA phantom with field uniformity and CT number accuracy modules accomplishes all monthly CT simulator QA tasks recommended by TG-66. The modular design allows for further customization if future additional tests are desired or recommended. Further investigation is needed to assess the integrity of 3D printed materials after multiple irradiations. Future work includes the development of image quality modules.