What is the difference between standard IMRT QA and IMRT QA with COMPASS?
Patient-specific IMRT QA can be done in two ways. Fieldwise verification, using a 2D detector (film or electronic detector) with some build-up with perpendicular incident beam. The second option is to use the film or electronic detector placed in a phantom. In both cases the dose to the patient is not verified directly, but a hybride plan using the original patient’s fields applied to the phantom geometry and composition is created. Therefore, the verification does not use the original patient anatomy as defined in the planning CT. Dose computation does not include the effect of inhomogeneity, nor can it evaluate the effect of delivery discrepancies to the target and organ at risk structures. COMPASS can determine the 3D dose distribution in the patient anatomy, based on the measured beam intensity. Therefore, it directly addresses the expected clinical consequences of delivery discrepancies, which are evaluated (among other representations) as DVH for target and OAR structures.
