Room: AAPM ePoster Library
To ensure accurate dose delivery in external beam radiotherapy, treatment plans can be delivered to a quality assurance device prior to treatment. For this purpose, an array of small detectors (~1mm) with sub millimeter spacing between them is required. We propose optical imaging as quality assurance tool (QA) for imaging highly modulated radiotherapy treatment plans.
A water equivalent cylindrical water phantom doped with a fluorophore was used in this study. Radioluminescence generated in response to the radiation beam was imaged using two intensified cameras. The couch mounted camera was used to image the front face of the phantom. The gantry mounted camera was used for imaging the photon fluence incident on the phantom surface. To facilitate imaging of the surface of the cylinder, a scintillating sheet was wrapped around the curved surface of the phantom. First, a clinical radiosurgery multi-target plan was delivered to the water phantom. The plan was imaged using a single camera near the foot of the couch and compared to the dose distribution generated by the TPS. Next, static 3 x 3 cm², 7 x 7 cm² beam and a static MLC defined aperture simulating a typical control point for a multi-target SRS plan were delivered to the phantom and reconstructed in 3D.
The final 3D volumes for the static beams were reconstructed at a voxel size of 0.5 mm³. Spatial resolution of the optical imaging system was measured as ~1 mm. For the multi-target radiosurgery plan, the projected 2D dose distribution exhibited a 98% passing rate for the 5%/1mm gamma criteria when compared to the projected 2D treatment planning system (TPS) dose distribution.
Optical imaging enables evaluation of highly modulated radiosurgery plans in 2D, 3D and 4D.
Funding Support, Disclosures, and Conflict of Interest: The authors acknowledge the Irradiation Shared Resource at the Norris Cotton Cancer Center at Dartmouth with NCI Cancer Center Support Grant P30 CA023108 and the NIH Grant: R01 EB023909. Brian Pogue reports financial interest in DoseOptics LLC, a company developing cameras and software for the use of Cherenkov imaging.