Exploring the Use of Contour-Based Intrafraction Motion Review for Spine Stereotactic Body Radiation Therapy Treatments.

Purpose: Patient motion during radiation therapy treatment is a concern, especially for spine stereotactic body radiation therapy cases where the sharper dose gradient presents a toxicity threat to the spinal cord. Intrafraction motion review (IMR) is an application used to monitor patient position during treatment. The presence of spinal fixation hardware presents an opportunity for motion tracking to manually pause the beam. Methods and Materials: A cohort of 17 clinicians were shown a video of the imaging console during a simulated treatment. Participants decided after each triggered image if they would pause the treatment beam, indicating that they believed the phantom to have moved outside of clinical tolerance. A spine phantom with hardware intact was positioned on a motion platform, which was programmed to make shifts ranging in size from 0.5 to 1.5 mm. A 1-mm isotropic expansion contour from the hardware was overlayed on the triggered planar x-ray images using the IMR application. Results: User perception sensitivity did not exceed 0.5 until there was a physical shift of 1.4 mm, indicating that most users will not be able to reliably discriminate submillimeter shifts using contour-based shift identification. Conclusions: If adaptations to standard of care are implemented clinically, the proposed method should be evaluated and the role of training and education should be examined before implementation. However, contour-based IMR could still provide beneficial information for larger intrafraction motion during treatment and could be valuable for identifying gross anatomic motion during treatment.