Dosimetric Effect of Intra-Fraction Motion in Multiple Brain Metastases SRS/SRT: An Evaluation Based On a Robotic Radiosurgery System
Presentations
MO-C930-IePD-F7-5 (Monday, 7/11/2022) 9:30 AM - 10:00 AM [Eastern Time (GMT-4)]
Exhibit Hall | Forum 7
Purpose: SRS/SRT treating multiple lesions is increasingly used for brain metastasis management. However, the treatment accuracy may be sensitive to patient motion for treatment with considerable inter-target distance. This study aimed to evaluate the dosimetric effect of intra-fraction motion during SRS/SRT by incorporating patient motion tracking data in order to provide useful clinical data.
Methods: Five patient with a total of 64 lesions (11 -14 lesions per patient) were included who were treated using a single CyberKnife plan. Patient intra-fraction motion, defined as position offset from the planned position was analyzed for each patient. The motion including patient’s translation in anterior-posterior, superior-inferior, left-right directions as well as rotation (i.e., yaw, pitch and roll) was calculated through registering KVs to plan DRRs. These intra-fraction motion data of each patient were then used to calculate the shift of each lesion for that patient. The dose after lesion shift was re-calculated using the original plan and the DVH for each lesion was compared to that of the original plan.
Results: The shift of lesions has a range of [0.5, 2.3]mm (mean: 1.3+/-0.44mm) due to patient intra-fraction motion. The Rx dose coverage for each lesion changed from average 99.6% (range: 98% - 100%) to average 91.9% (range: 74.2% - 100%). The target coverage reduction is associated with the target distance to the treatment isocenter.
Conclusion: Intra-fraction motion can induce a significant drop of the target dose coverage for certain lesions during multiple-target brain SRS/SRT (e.g., up to 24.6% reduction). Motion compensation is definitely needed as is used in Cyberknife or a proper motion reduction device should be used for linac-based multiple-target brain SRS/SRT.
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