Tomographic‐based 3D scintillation dosimetry using a three‐view plenoptic imaging system

• Published in: Medical physics (Lancaster) 2020-08, Vol.47 (8), p.3636-3646
• Main Authors: Rilling, Madison, Allain, Guillaume, Thibault, Simon, Archambault, Louis
• Format: Article
• Language: English
• Subjects: 3D dosimetry; Algorithms; optical imaging; Photons; plenoptic camera; Radiometry; scintillation; tomographic reconstruction; Tomography, X-Ray Computed
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1002/mp.14213

Purpose To demonstrate the feasibility of a three‐plenoptic camera projection, scintillation‐based dosimetry system for measuring three‐dimensional (3D) dose distributions of static photon radiation fields. Methods Static x‐ray photon beams were delivered to a cubic plastic scintillator volume embedded within acrylic blocks. For each beam, three orthogonal projections of the scintillating light emission were recorded using a multifocus plenoptic camera. Experimental 3D reconstructions of the light distribution were obtained using an iterative maximum likelihood‐expectation maximization (ML‐EM) algorithm. For this purpose, the elements of the system matrix representing the contribution of the scintillator volume voxels to the camera sensor pixels were calculated using optical design software. A reconstruction‐specific correction was applied to light reconstructions to account for scintillating light imaged by the camera but not directly resulting from dose deposition. Cross beam profiles (CBPs) and percentage depth dose (PDD) curves were compared to treatment planning system data for square fields. Three‐dimensional and 3D gamma analyses were performed for concave‐shaped dose distributions and the Pearson correlation coefficient and reconstruction error were employed to assess the quality of the measured relative 3D dose distributions. Results A full and accurate model of the plenoptic camera‐based scintillation dosimetry system was implemented using the light ray tracing capabilities of optical design software. With this model, light distributions were successfully reconstructed over a volume of 60 × 60 × 60 mm3 at a resolution of 2 mm. For relative 3D measurements of square radiation fields of 2×2cm2, 3×3cm2 and 4×4cm2 compared with treatment planning system reference distributions, the maximum root‐mean‐square error of the CBPs evaluated at two different depths was of 3.2%, 1.2%, and 1.1%, respectively; as for the corresponding linearly fitted PDDs of the square fields, the slopes of the reconstructed dose distributions overestimated those of the reference distributions by at most 0.2%/ cm. The 2D gamma passing rate with a criterion of 2%/2 mm for the concave‐shaped photon field was of 61.6%, 66.1%, and 76.4% using one, two, and three plenoptic projections; the respective success rates become 77.1%, 87.5%, and 94.9% using a criterion of 3%/3 mm. The 3D correlation coefficient for the corresponding reconstructions was of 0.688, 0.905, and 0.976, respectiv