Quality assurance for a six degrees‐of‐freedom table using a 3D printed phantom

Abstract

PurposeTo establish a streamlined end‐to‐end test of a 6 degrees‐of‐freedom (6DoF) robotic table using a 3D printed phantom for periodic quality assurance.MethodsA 3D printed phantom was fabricated with translational and rotational offsets and an imbedded central ball‐bearing (BB). The phantom underwent each step of the radiation therapy process: CT simulation in a straight orientation, plan generation using the treatment planning software, setup to offset marks at the linac, registration and corrected 6DoF table adjustments via hidden target test, delivery of a Winston‐Lutz test to the BB, and verification of table positioning via field and laser lights. The registration values, maximum total displacement of the combined Winston‐Lutz fields, and a pass or fail criterion of the laser and field lights were recorded. The quality assurance process for each of the three linacs were performed for the first 30 days.ResultsWithin a 95% confidence interval, the overall uncertainty values for both translation and rotation were below 1.0 mm and 0.5° for each linac respectively. When combining the registration values and other uncertainties for all three linacs, the average deviations were within 2.0 mm and 1.0° of the designed translation and rotation offsets of the 3D print respectively. For all three linacs, the maximum total deviation for the Winston‐Lutz test did not exceed 1.0 mm. Laser and light field verification was within tolerance every day for all three linacs given the latest guidance documentation for table repositioning.ConclusionThe 3D printer is capable of accurately fabricating a quality assurance phantom for 6DoF positioning verification. The end‐to‐end workflow allows for a more efficient test of the 6DoF mechanics while including other important tests needed for routine quality assurance.

3D printing technology will eventually eliminate the need of purchasing commercial phantoms for clinical medical physics QA procedures

“…In most clinics, the Linac morning QA is performed with a commercial image guidance radiotherapy (IGRT) phantom, which is a cubic phantom with marks on the faces for laser alignment and embedded features for x‐ray imaging. An IGRT phantom with submillimeter accuracy was fabricated and reported by Woods et al . using computer‐aided design freeware and a relatively low cost 3D printer (commercially available for $3150 USD).…”

Dosimetric Evaluation of Commercially Available Flat vs. Self-Produced 3D-Conformal Silicone Boluses for the Head and Neck Region

“…In radiotherapy, the 3D printing fused deposition modeling (FDM) technique introduced by Crump (1) has been used in a variety of ways including the creation of individualized phantoms, brachytherapy applicators, or intraoral stents (2)(3)(4). The fabrication of individualized boluses via 3D printing represents another application of this technique.…”

Technical Note: an algorithm and software for conversion of radiotherapy contour‐sequence data to ready‐to‐print 3D structures

“…The clinical benefits of implementing 3D‐printing technology for radiation oncology include improvement in dose distribution uniformity and better sparing of organs at risk by individualization of phantoms, boluses and brachytherapy applicators. Moreover, single‐institution experiences show the potential of applying 3D technology for printing couplant pads for ultrasound image‐guided radiation therapy, electron beam aperture cut‐outs, masks, oral stents, stepless beam modulators or range compensators in proton therapy, and templates for brachytherapy …”