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Prospective Treatment Plan-Specific Action Limits for Real-Time Intrafractional Monitoring in Surface Image Guided Radiosurgery

A Yock

A Yock*, T Pawlicki, G Kim, University of California, San Diego, La Jolla, CA


SU-G-JeP4-11 (Sunday, July 31, 2016) 5:30 PM - 6:00 PM Room: ePoster Theater

Surface image-guided radiosurgery action limits are created to determine when intrafractional patient motion warrants intervention. Action limits remain constant across patients despite plan-specific effects on brain metastases target coverage. The purpose of this work was twofold: 1) characterize the sensitivity of single-met per iso and multi-met per iso treatment plans to motion, and 2) describe a method to prospectively determine plan-specific action limits considering this sensitivity.

Seventy-two brain metastases were used for this study. Twenty-five were treated individually (“single-met per iso plans”), and 47 were treated simultaneously with at least one other met (“multi-met per iso plans”). For each met, the proportion of the gross tumor volume that remained within the 100% prescription isodose line after various combinations of translations and rotations (0.0–3.0 mm and 0.0–3.0°) was estimated. This was achieved using code developed in the Matlab environment that exhaustively evaluated the effects of all combinations of translations and rotations in this range. The target volume and the prescription dose volume were considered concentric spheres that encompassed volumes determined from the treatment plan. Plan-specific contour plots and DVHs were created to illustrate the sensitivity of a specific lesion to motion.

Both single-met per iso and multi-met per iso plans exhibited compromised target coverage after transformations, though multi-met per iso plans were considerably more sensitive to motion (2.3% and 39.8%, respectively). Plan-specific contour plots and DVHs illustrate how size, distance from isocenter, and planning technique affect motion sensitivity.

Stereotactic radiosurgery treatment plans that treat multiple brain metastases using a common isocenter are particularly susceptible to patient motion. This technique and other plan-specific factors should influence motion management. A graphical representation of the sensitivity of any plan to motion can be generated to determine appropriate action limit.

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