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Material Matters: Concerns with 3D Printed Material Consistency

D Craft

D F Craft*, R M Howell , UT MD Anderson Cancer Center, Houston, TX


SU-I-GPD-T-217 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: 3D printers have recently been used to fabricate tissue compensators, proton range compensators, bolus for various anatomical sites, and numerous radiotherapy and imaging phantoms. Many of these studies have reported Hounsfield units for the material they used, but HU values are inconsistent between studies. The purpose of this study was to [1] determine the variance in HU for printed objects over time, and [2] determine if HU variance depends on the storage environment.

Methods: For PLA, ABS, NinjaFlex, and Cheetah materials (commonly used for medical physics applications) we printed two blocks of each material every week for 6 weeks. The material spools were opened at the beginning of the experiment and left in an open air environment. For each material type, one printed block was stored in a bag with desiccant, and one was left out. Each week every block was CT scanned and the HU was recorded.

Results: Individual new blocks of PLA, ABS, NinjaFlex, and Cheetah varied by as much as 121, 30, 178, and 30 HU respectively. There was considerably less variation for individual blocks after being printed, and there was no systematic drift of new blocks increasing or decreasing in HU. Cheetah and ABS had the least variation between blocks, and Cheetah and PLA had the least variation week-to-week. Using desiccant bags made a small difference in HU variance for NinjaFlex and ABS. NinjaFlex HU increased by 17 HU without desiccant, and decreased by 12 HU with it, while those numbers are 8 and 2 HU respectively for ABS. Cheetah and PLA showed minimal differences with or without desiccant.

Conclusion: While week-to-week HU variance for individual objects is low, different objects can vary in HU greatly. Whenever using a 3D-printed device in radiotherapy, HU must be determined for that object individually, and occasionally rechecked.

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