Application of optical photogrammetry in radiation oncology: HDR surface mold brachytherapy

Brachytherapy. Sep-Oct 2019;18(5):689-700. doi: 10.1016/j.brachy.2019.05.006. Epub 2019 Jun 20.

Abstract

Purpose: We propose a novel method of designing surface mold brachytherapy applicators using optical photogrammetry. The accuracy of this technique for the purpose of 3D-printing surface mold brachytherapy applicators is investigated.

Methods and materials: Photogrammetry was used to generate a 3D model of a patient's right arm. The geometric accuracy of the model was evaluated against CT in terms of volume, surface area, and the Hausdorff distance. A surface mold applicator was then 3D printed using this reconstructed model. The accuracy was evaluated by analyzing the displacement and air-gap volumes between the applicator and plaster cast on a CT image. This technique was subsequently applied to generate a 3D-printed applicator of the author's hand directly, as a proof of principle, using only photographic images.

Results: The volume and surface area of the model were within 0.1% and 2.6% of the CT-obtained values, respectively. Using the Hausdorff distance metric, it was determined that 93% of the visible vertices present in the CT-derived model had a matching vertex on the photogrammetry-derived model within 1 mm, indicating a high level of similarity. The maximum displacement between the plaster cast of the patient's arm and the photo-derived 3D-printed applicator was 1.2 mm with a total air-gap volume of approximately 0.05 cm3.

Conclusions: Photogrammetry has been applied to the task of generating 3D-printed brachytherapy surface mold applicators. The current work demonstrates the feasibility and accuracy of this technique and how it may be incorporated into a 3D-printing brachytherapy workflow.

Keywords: AliceVision; Blender; Bolus; Brachytherapy; Photogrammetry; Slicer 3D; Surface mold.

MeSH terms

  • Arm / anatomy & histology
  • Arm / diagnostic imaging
  • Brachytherapy / instrumentation*
  • Brachytherapy / methods*
  • Casts, Surgical
  • Computer-Aided Design
  • Equipment Design
  • Feasibility Studies
  • Humans
  • Imaging, Three-Dimensional / methods
  • Models, Anatomic
  • Photogrammetry / methods*
  • Printing, Three-Dimensional*
  • Radiotherapy Dosage
  • Radiotherapy Planning, Computer-Assisted / methods
  • Tomography, X-Ray Computed / methods