Click here to


Are you sure ?

Yes, do it No, cancel

A Quantitative Test Tool for the Gamma Knife Icon Intra-Fraction Motion Management (IFMM) System

J Napoli1*, I Rebo1 , L Napoli2 , A Ndlovu1 , (1) Hackensack Univ Medical Center, Hackensack, NJ, (2) RCA Research Center ,Long Beach Township, NJ


(Wednesday, 7/17/2019) 9:30 AM - 10:00 AM

Room: Exhibit Hall | Forum 6

Purpose: Elekta’s Gamma Knife Icon unit incorporates an intrafraction motion management system which enables treatment to be delivered in a gated fashion. Stationary reflectors are placed on the mask mount and a patient reflector is placed at the tip of the patient’s nose. Baseline position is established during CBCT. Movement of the patient reflector outside a preset tolerance will trigger a beam hold. Once the patient reflector moves back to within tolerance, the treatment resumes. If the patient marker moves outside of the tolerance level more than 5 times or for 30 consecutive seconds during one shot, the treatment will pause. Although some regulatory jurisdictions require periodic quantitative assessments of the IFMM, we are unaware of a commercially-available tool with which to measure it. The purpose of this work was the design of a precision tool to assess the system’s ability to accurately detect movement, and to react appropriately to movements outside the tolerance level.

Methods: We utilized a commercially-available linear stage to precisely move the IFMM’s patient reflector in each of the three orthogonal axes while observing the system’s reported movement. The operator then remotely moves the patient marker out of and back within tolerance during a shot, and observes the application or release of a beam hold. When the marker is moved more than five times during a single shot, or remains outside the tolerance level for 30 seconds, the system pauses.

Results: We have found the tool to be accurate to within 0.2mm versus the IFMM system, and that the system pauses when appropriate.

Conclusion: This simple tool can be used to assess both the accuracy and the gating function of the system’s infrared tracking system.


Gamma Knife, Patient Movement, Quality Assurance


TH- External beam- photons: Motion management (intrafraction)

Contact Email