Megavoltage CT imaging as a by-product of multileaf collimator leakage

In addition to their potential for the delivery of highly conformal radiati on therapy treatments, tomotherapeutic treatments also Feature increased po tential for verification. For example, megavoltage CT allows one to use the megavoltage linac to generate tomographic images of the patient in the tre atment position. This is typically done before or after radiation therapy t reatments. However, it is also possible to collect MVCT images entirely dur ing the treatment itself. This process utilizes the leakage radiation throu gh the closed leaves of the Nomos MIMiC MLC, along with slight inefficienci es in treatment delivery, to generate MVCT images during treatment that req uire neither additional time nor dose. The image quality is limited, yet su fficient to see a patient's external boundary, density differences over 8% for 25.0 mm objects and resolutions of 3.0 mm for high-contrast objects. Su ch images can potentially be viewed during treatment, used to flag addition al CT immediately after the treatment and provide a representation of the p atient's exact position during treatment for use with dose reconstruction.