Evaluation of camera settings for photogrammetric reconstruction of humanoid phantoms for EBRT bolus and HDR surface brachytherapy applications

The fabrication of brachytherapy surface moulds is considered laborious and time consuming that often result in repeated attempts due to incorrect catheter positioning or the presence of air gaps. 3-dimensional printing using low-cost and reliable materials has allowed the rapid creation of patient-specific surface mould applicators to be achieved using patient imaging data obtained via CT scan. In this study we investigate whether an alternative approach using photogrammetry techniques can improve this process and how camera settings and object texture affect the reconstructions. Two humanoid phantoms, an anthropomorphic RANDO phantom and a Laerdal Little Anne CPR training manikin were used in this study. Both were imaged using a Nikon D5600 DSLR and Nokia 3.1 smartphone camera and reconstructed using Agisoft Metashape software. CT scans of both phantoms were taken as references for comparing the photogrammetry reconstructions. Models were reconstructed from different photo sets and assessed by distance to agreement with the CT models. Both phantoms were effectively reconstructed for most experiments. Increasing the number of photos used produced the better reconstructions while in general, reconstructions using video data were poor. The two phantoms were reconstructed at a similar quality. Background light that caused undesirable reflections significantly reduced reconstruction quality. Applying a non-reflective tape to the affected regions provided a suitable method for reducing their effects. Photogrammetry techniques were effectively able to reconstruct 3-dimensional models of both phantom. The camera settings and lighting did have a profound effect on the reconstruction quality and should be chosen appropriately depending on the scene.

Automated summary

Photogrammetry techniques can effectively improve the fabrication process of brachytherapy surface moulds, while camera settings and object texture have a significant impact on the quality of reconstruction and should be chosen appropriately depending on the scene.