Intra-Fraction Motion of Brain SRS/SRT with Multiple Targets: an Evaluation Based On a Robotic Radiosurgery System
X Chen*, L Jin, L Chen, J Liu, L Wang, S Hayes, S Weiss, R Price, C Ma, Fox Chase Cancer Center, Philadelphia, PA
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PO-GePV-T-391 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: Concurrent multiple target SRS/SRT is increasingly used for brain metastasis management. However, the accuracy of dose delivery is sensitive to patient motion for plan with considerable inter-target distance. This study aimed to evaluate the intra-fraction motion during SRS/SRT by analyzing patient motion tracking data and may provide useful clinical data.
Methods: 40 treatment fractions from 12 patients were included who were treated for 8-15 targets in a single plan with Cyberknife. Patient intra-fraction motion, defined as position offset from plan position, was calculated through registering KVs to plan DRRs. Orthogonal KV pairs were acquired every ~20 seconds during treatment. These motion data were retrieved in treatment log files and processed to include 5016 on-treatment time points. Patient’s translation in anterior-posterior, superior-inferior, left-right directions as well as rotation (i.e., yaw, pitch, roll) were analyzed.
Results: The distance of translation has a range of [0, 3.9]mm (mean: 0.84+/-0.43mm). For each direction, these values are [-3.3, 2]mm (mean: -0.03+/-0.57mm) in S-I, [-2.3, 2.7]mm (mean: -0.04+/-0.62mm) in L-R, [-1.8, 2.1]mm (mean: 0.08+/-0.41mm) in A-P. Patient rotation has a range of [-2.8, 2.1]º with a mean -0.1+/-0.7º for yaw, [-1.8, 3.1]º (mean: -0.19+/-0.57º) for pitch, and [-2.0, 1.9]º (mean: 0.0+/-0.45º) for roll. Results also show 71.8% of time patients move <1mm distance, and 97.9% (<2mm). For patient rotation, 47.4% of time is for < 0.5º yaw and 83.8% (<1º). These values are 51.5%(<0.5º) and 91.3%(<1º) for pitch, and 74.4%(<0.5º) and 97.5%(<1º) for roll.
Conclusion: Most of intra-fraction motion is <2mm (97.9% of time). However, patient’s yaw rotation seems significant with only 83.8% of time <1º . With 1.8mm offset caused by 1º rotation for a 10cm inter-target distance, this means ~16% of time, targets away from the isocenter may have ~2mm offset versus plan position (~1 mm for targets 5cm away from isocenter).
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