Abstract
We conducted a comprehensive evaluation of the clinical accuracy of an image‐guided frameless intracranial radiosurgery system. All links in the process chain were tested. Using healthy volunteers, we evaluated a novel method to prospectively quantify the range of target motion for optimal determination of the planning target volume (PTV) margin. The overall system isocentric accuracy was tested using a rigid anthropomorphic phantom containing a hidden target. Intrafraction motion was simulated in 5 healthy volunteers. Reinforced head‐and‐shoulders thermoplastic masks were used for immobilization. The subjects were placed in a treatment position for 15 minutes (the maximum expected time between repeated isocenter localizations) and the six‐degrees‐of‐freedom target displacements were recorded with high frequency by tracking infrared markers. The markers were placed on a customized piece of thermoplastic secured to the head independently of the immobilization mask. Additional data were collected with the subjects holding their breath, talking, and deliberately moving. As compared with fiducial matching, the automatic registration algorithm did not introduce clinically significant errors (<0.3 mm difference). The hidden target test confirmed overall system isocentric accuracy of ≤1 mm (total three‐dimensional displacement). The subjects exhibited various patterns and ranges of head motion during the mock treatment. The total displacement vector encompassing 95% of the positional points varied from 0.4 mm to 2.9 mm. Pre‐planning motion simulation with optical tracking was tested on volunteers and appears promising for determination of patient‐specific PTV margins. Further patient study is necessary and is planned. In the meantime, system accuracy is sufficient for confident clinical use with 3 mm PTV margins.PACS number: 87.53.Ly
Highlights
69 Feygelman et al.: Simulation of intrafraction motion and overall geometric...method requires careful assessment
The studies reported in the literature do not adequately answer all the questions pertaining to the practical clinical implementation of the BrainLAB (Feldkirchen, Germany) frameless SRS system (Novalis), in terms of the overall accuracy of the whole treatment chain, as emphasized in Mack et al[8]
This limitation is important for the Novalis system, in which imaging is less frequent than it is in CyberKnife, and to assure adequate target coverage in the presence of intrafraction motion, more reliance must be placed on judiciously expanded planning target volume (PTV) margins than on frequent positional adjustments
Summary
69 Feygelman et al.: Simulation of intrafraction motion and overall geometric...method requires careful assessment. Very useful for acquisition of population-based statistics and for retrospective analysis, these studies show a great deal of variability between cases, and as a result, they have limited predictive value for individual patients, for single-fraction SRS This limitation is important for the Novalis system, in which imaging is less frequent than it is in CyberKnife, and to assure adequate target coverage in the presence of intrafraction motion, more reliance must be placed on judiciously expanded planning target volume (PTV) margins than on frequent positional adjustments
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