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A Method for the Production of 3D-Printed Compensators for Superficial X-Ray Radiotherapy

B Loughery

B Loughery*, M Snyder , Karmanos Cancer Center / Wayne State University, Detroit, MI


SU-I-GPD-T-500 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Superficial x-ray radiotherapy (SXRT) treats basal cell carcinomas and breast scars. It is desirable to deliver uniform surface dose across the patient-specific contour of a tumor site, but this desire is impeded by beam divergence and the heel effect. We present a method to 3D-print a SXRT compensator that adjusts incident fluence to achieve equal dose across a surface contour.

Methods: We first characterize the initial fluence of a superficial x-ray tube as a 2D function of position. A patient surface of interest is contoured from DICOM-CT, smoothed, simplified, and converted into a 3D-printable stereolitheography file (.STL) using open-source software. In .STL, a vertex maps each point on the patient surface. An in-house MATLAB package normalizes this map to originate at the tube focal spot and transforms each vertex as a ray length through the initial fluence function. Adjusted rays are modeled through exponential attenuation in a user-selected material to achieve uniform surface fluence. Calculated material thickness for each ray is projected to a flat plane at a predetermined distance from the source, which forms a 3D-printable model of a compensator. We tested this workflow on a 3D-printed breast scar phantom using PLA and a repurposed 120kVp portal imager. We irradiated the phantom for a set mAs with and without a compensator, taping OSLDs to the surface at eight locations for each measurement. We used these readings to calculate relative deviation from the central OSLD.

Results: OSLD measurements demonstrate that the compensator substantially improves dose deviations across the part contour. Crossplane maximum deviations improved from 17% to 2.0%, while inplane and diagonal deviations improved from over 25% each to approximately 10% each.

Conclusion: We can now print compensators that intentionally distort SXRT fluence into uniform dose at a surface. We hope this method will improve outcomes for superficial treatments.

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