Purpose: The GammaKnife (GK) Icon uses a High Definition Motion Management (HDMM) system to actively monitor patient motion during frameless SRS. The purpose of this study was to analyze immobilization techniques and patient motion during fractionated treatments on the GammaKnife Icon. The primary objective was to determine what immobilization device characteristics are related to patient stability using CBCT and HDMM imaging data.
Methods: Patient setup was evaluated using multiple techniques. At the time of treatment, error was assessed by comparing the simulation CBCT to the pretreatment CBCT and recording the shifts. During treatment, the number of gating events (i.e. HDMM alarms) and HDMM pauses were recorded. After the completion of treatment, the HDMM log file data containing spatial position data was exported for analysis. GammaKnife CBCT images were DICOM transferred to Velocity for analysis of immobilization device placement.
Results: The CBCT images and HDMM log file data were analyzed from a total of 27 GammaKnife Icon patients treated for a total of 106 fractions with mask immobilization. There was a total of 216 HDMM alerts that resulted in a temporary gated treatment state. Most fractions (79%) had no HDMM pauses or treatment interruptions. A total of 30 treatment sessions had HDMM pauses with patient motion exceeding the limiting threshold. Analysis of the CBCT images indicated that the major cause of HDMM pauses was incorrect patient positioning in the immobilization device at the beginning of the treatment session. HDMM log file data indicated that patients with the aquaplastic mask molded around the custom head cushion were more stable.
Conclusion: Patient motion during treatment was minimized in patients when the mask was molded around the head cushion. Patients with unsatisfactory immobilization were more likely to have multiple pauses in the same treatment session.
Gamma Knife, Immobilization, Optical Imaging
TH- External Beam- Photons: Motion management - intrafraction