TU‐C‐108‐02: Novel Full 3D Water‐Equivalent Dosimetry Technique Using a Single Light‐Field Camera for Photons, Electrons and Ion‐Beams Dosimetry

Purpose: Using an array of micro‐lenses coupled with its active sensor, a light‐field camera samples the incoming optical photons in both the spatial and angular domain. This work presents the proof‐of‐concept and experimental validation of a 3D dosimeter based on the reconstruction of the light pattern emitted from a plastic scintillator volume and recorded using a light‐field camera. Using a single, fixed camera device, this technology enables real‐time, multi‐plane experimental measurement of static and dynamic radiotherapy delivery. Method: A Raytrix R5 light‐field camera was used to image a 10×10×10cm3 EJ‐260 plastic scintillator immersed in a water tank and irradiated with both square field and small MLC segments on a Clinac iX linear accelerator. The 3D light distribution emitted by the scintillator volume was reconstructed at a 5mm resolution in all dimensions by backprojecting the light collected by each pixel of the light‐field camera using a total variation minimization iterative reconstruction algorithm. Results: Signal contamination by Cerenkov emission was evaluated to less than 0.5% of the collected scintillation light for all field investigated, and as such Cerenkov light filtration was deemed unnecessary. Light‐field acquisition rate of at least 1 frame per second was achieved by the camera at a 600MU/min dose rate. The absolute dose difference between the reconstructed 3D dose and the expected dose calculated using the treatment planning software Pinnacle3 was on average below 3% for square fields and 5% for MLC segments in the high dose, low gradient region of each acquired field. Conclusions: Millimeter resolution dosimetry over an entire 3D volume is achievable in real‐time using a single light‐field camera. Because no moving parts are required in the dosimeter, the incident dose distribution can be acquired as a function of time, thus enabling the validation of static and dynamic radiation delivery with photons, electrons and ions.