Real Time 3D Beam Visualization for Monitoring External Beam Radiation Therapy

Abstract

The administration of radiation therapy has advanced steadily throughout its history. However, in spite of large advances in planning accuracy and motion tracking techniques, the actual administration of radiation continues to be a blind procedure. We propose that a system consisting of a flexible scintillation sheet and an array of digital cameras can be used to simultaneously visualize the patient surface and the delivered radiation beam in three dimensions and in real time. For the proof of concept system, scintillating sheets were made by mixing Gd2O2S:Tb (GOS) with silicone and casting the mixture into a thin sheet. The sheet was placed on a solid water phantom and irradiated with therapeutic photon beams from a medical linear accelerator (LINAC). The light emitted from the sheet was collected using a pair of cameras calibrated as a stereo pair. Custom designed image processing software was used to reconstruct the 3D scene and extract the beam profile. The shape and location of the extracted profile was compared to known collimator settings for validation. The system was capable of acquiring high quality images of both the phantom and the beam under various levels of ambient room lighting including those most commonly used during therapy. Images were obtained at a rate of 20 fps. The system demonstrated sub-millimeter resolution and accuracy in identifying both the shape and location of radiation beams. The intensity of the beam profile was found to be linear with dose rate and correlated to the expected surface dose as beam energy changes. A system consisting of digital cameras and a flexible scintillation sheet is capable of three dimensional visualization of external beam radiation therapy in real-time. The accuracy of the data is sufficient that further development of the system may provide the ability to verify the accuracy of treatment as it is occurring and provide a record for post-treatment analysis.