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Intra-Fraction Motion Management for Radiosurgical Treatments of Trigeminal Neuralgia: Clinical Experience and Motion Analysis

N Agazaryan

N Agazaryan*, A Sharma, D Low, UCLA School of Medicine, Los Angeles, CA

SU-E-J-26 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

To evaluate the patient positioning and intra-fraction motion management performance of an image-guidance protocol established for radiosurgical treatments of trigeminal neuralgia patients. Specifically, to analyze patient data for the evaluation of current motion tolerance levels utilized for repositioning.

NovalisTx equipped with Exactrac is used for stereoscopically positioning and treatments. Treatments are delivered with 4mm collimator using 7 equally spaced arcs that are 20 degrees apart and span 100 arc degrees each. Following initial Exactrac positioning, CBCT is obtained for independent confirmation of patient position. Patient is then stereoscopically imaged prior to the delivery of each arc and repositioned when 0.5mm translational tolerance in any direction is exceeded. Data from 48 patients with 607 image pairs has been analyzed.

The mean magnitude of 3D deviation was 0.64mm±0.12mm (range 0.07-2.74mm). With the current 0.50mm tolerance level for repositioning, patients exceeded the tolerance 51.4% of the time considering only images following an arc delivery. For those instances, patients were repositioned with a mean magnitude of 0.85mm±0.15mm. With 0.75mm and 1.00mm tolerance limits, the tolerance would have been exceeded only 21.5% and 6.6% of the time, with a mean magnitude of 1.08mm±0.21mm and 1.34mm±0.24mm respectively.

Current 0.50mm tolerance level results in a significant number of patient repositions that result from actual patient motion convolved with the accuracy and precision of the image analysis. Relaxing the re-positioning tolerance could more selectively correct for actual patient motion at the expense of more variations in patient position. A 0.75mm would decrease the repositioning rate by approximately a factor of two; however, the permissible magnitude of motion will increase, leading to possible dosimetric consequences. Once treatment begins, there was no trend as to when patients exceeded the tolerance. Future analysis will include quantitative dosimetric consequences due to intra-fraction motion.

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