Program Information
The Continuous Assessment of Cranial Motion in Thermoplastic Masks During CyberKnife Radiosurgery
A Mayville*, T Bichay , Saint Mary's Health Care, Grand Rapids, MI
Presentations
SU-I-GPD-T-82 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: Stereotactic radiosurgery (SRS) treatment is characterized by high doses per fraction and extremely high dose gradients. This requires a great degree of accurate localization to the appropriate treatment position, and continuous immobilization during the treatment session. In this study we carried out a quantitative analysis of patient motion during the full treatment fraction within a radiosurgery immobilization mask system.
Methods: Patient cranial movement was assessed by using the image guidance stereo x-ray cameras on a CyberKnife (CK) M6 robotic radiosurgery system (Accuray, Sunnyvale, CA). A total of 15 patients received treatments for intracranial lesions. The treatment delivery sessions varied from 13-42 minutes. Orthogonal images were taken every 15-30 seconds during the treatment to assess patient movement. Approximately 43 stereo images were taken per patient and a total of 641 image pairs were analyzed in this study.
Results: The mean absolute deviation from baseline in the longitudinal, lateral and vertical directions was approximately 0.52, 0.26, and 0.25 mm respectively for the duration of treatments. However, on occasion much greater movement was observed during a fraction. The maximum displacement was in the longitudinal direction and reached 4.5 mm compared to the initial setup. Further, the average vector deviation from baseline for all treatments was 0.76 mm. The trends show that patient motion often stabilized after a significant motion event.
Conclusion: This data suggests that although this mask system appears stable during much of the treatment session; for some patients there may be momentary movements that take place. Continuous imaging and correction can help mitigate the effect of this movement. It is important to understand the limitations of non-invasive mask systems when used for very high precision treatments.
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