Investigating the impacts of intrafraction motion on dosimetric outcomes when treating small targets with virtual cones.

Intrafraction patient motion is a well-documented phenomenon in radiation therapy. In stereotactic radiosurgery applications in which target sizes can be very small and dose gradients very steep, patient motion can significantly impact the magnitude and positional accuracy of the delivered dose. This work investigates the impact of intrafraction motion on dose metrics for small targets when treated with a virtual cone. Monte Carlo simulations were performed to calculate dose kernels for treatment apertures ranging from 1 × 2.5 mm The impact of motion on both the target and the surrounding tissue was a function of both aperture shape and target size. When a 0.5-mm linear drift along each dimension occurred during treatment, targets ≥5 mm saw less than a 10% decrease in coverage by the prescription dose. Smaller apertures accrued larger penalties with respect to dosimetric hotspots seen in the tissues surrounding the target volume during intrafraction motion. For example, treating a 4-mm-sized target that undergoes 2.60 mm (3D vector) of continuous linear motion, the D In this work, the dosimetric trade-offs between aperture size and target size when irradiating with virtual cones has been demonstrated. These findings provide information about the tradeoffs between target coverage and normal tissue sparing that may help inform clinical decision making when treating smaller targets with virtual cones.

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© 2021 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals LLC on behalf of American Association of Physicists in Medicine.