An evaluation of consumer smartphones for generating bolus and surface mould applicators for radiation oncology.

BACKGROUND: The use of Computed Tomography (CT) imaging data to create 3D printable patient-specific devices for radiation oncology purposes is already well established in the literature and has shown to have superior conformity than conventional methods. Using non-ionizing radiation imaging techniques such as photogrammetry or laser scanners in-lieu of a CT scanner presents many desirable benefits including reduced imaging dose and fabrication of the device can be completed prior to simulation. With recent advancements in smartphone-based technology, photographic and LiDAR-based technologies are more readily available than ever before and to a high level of quality. As a result, these non-ionizing radiation imaging methods are now able to generate patient-specific devices that can be acceptable for clinical use. PURPOSE: In this work, we aim to determine if smartphones can be used by radiation oncologists or other radiation oncology staff to generate bolus or brachytherapy surface moulds instead of conventional CT with equivalent or comparable accuracy. METHODS: This work involved two separate studies: a phantom and participant study. For the phantom study, a RANDO anthropomorphic phantom (limited to the nose region) was used to generate 3D models based on three different imaging techniques: conventional CT, photogrammetry & LiDAR which were both acquired on a smartphone. Virtual boli were designed in Blender and 3D printed from PLA plastic material. The conformity of each printed boli was assessed by measuring the air gap volume and approximate thickness between the phantom & bolus acquired together on a CT. For the participant study, photographs, and a LiDAR scan of four volunteers were captured using an iPhone 13 Pro™ to assess their feasibility for generating human models. Each virtual 3D model was visually assessed to identify any issues in their reconstruction. The LiDAR models were registered to the photogrammetry models where a distance to agreement analysis was performed to assess their level of similarity. Additionally, a 3D virtual bolus was designed and printed using ABS material from all models to assess their conformity onto the participants skin surface using a verbal feedback method. RESULTS: The photogrammetry derived bolus showed comparable conformity to the CT derived bolus while the LiDAR derived bolus showed poorer conformity as shown by their respective air gap volume and thickness measurements. The reconstruction quality of both the photogrammetry and LiDAR models of the volunteers was inadequate in regions of facial hair and occlusion, which may lead to clinically unacceptable patient-specific device that are created from these areas. All participants found the photogrammetry 3D printed bolus to conform to their nose region with minimal room to move while three of the four participants found the LiDAR was acceptable and could be positioned comfortably over their entire nose. CONCLUSIONS: Smartphone-based photogrammetry and LiDAR software show great potential for future use in generating 3D reference models for radiation oncology purposes. Further investigations into whether they can be used to fabricate clinically acceptable patient-specific devices on a larger and more diverse cohort of participants and anatomical locations is required for a thorough validation of their clinical usefulness.

A dosimetric comparison of CT- and photogrammetry- generated 3D printed HDR brachytherapy surface applicators.

In this study, we investigate whether an acceptable dosimetric plan can be obtained for a brachytherapy surface applicator designed using photogrammetry and compare the plan quality to a CT-derived applicator. The nose region of a RANDO anthropomorphic phantom was selected as the treatment site due to its high curvature. Photographs were captured using a Nikon D5600 DSLR camera and reconstructed using Agisoft Metashape while CT data was obtained using a Canon Aquillion scanner. Virtual surface applicators were designed in Blender and printed with PLA plastic. Treatment plans with a prescription dose of 3.85 Gy × 10 fractions with 100% dose to PTV on the bridge of the nose at 2 mm depth were generated separately using AcurosBV in the Varian BrachyVision TPS. PTV D98%, D90% and V100%, and OAR D0.1cc, D2cc and V50% dose metrics and dwell times were evaluated, with the applicator fit assessed by air-gap volume measurements. Both types of surface applicators were printed with minimal defects and visually fitted well to the target area. The measured air-gap volume between the photogrammetry applicator and phantom surface was 44% larger than the CT-designed applicator, with a mean air gap thickness of 3.24 and 2.88 mm, respectively. The largest difference in the dose metric observed for the PTV and OAR was the PTV V100% of - 1.27% and skin D0.1cc of - 0.28%. PTV D98% and D90% and OAR D2cc and V50% for the photogrammetry based plan were all within 0.5% of the CT based plan. Total dwell times were also within 5%. A 3D printed surface applicator for the nose was successfully constructed using photogrammetry techniques. Although it produced a larger air gap between the surface applicator and phantom surface, a clinically acceptable dose plan was created with similar PTV and OAR dose metrics to the CT-designed applicator. Additional future work is required to comprehensively evaluate its suitability in a clinically environment.

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.