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A Simple Tool to Assess the Gamma Knife Icon IFMM System

J Napoli1*, L Napoli2 , j barbiere3 , A Ndlovu4 , (1) Hackensack university Medical Center, Hackensack, NJ, (2) RCA Research Laboratory (Ret.), Long Beach Township, NJ, (3) ,,,(4) Hackensack university Medical Center, Hackensack, NJ


(Monday, 7/30/2018) 1:15 PM - 1:45 PM

Room: Exhibit Hall | Forum 6

Purpose: Icon, the current model of Elekta’s Gamma Knife unit, offers a mask-based immobilization system, intended to be used for fractionated treatments, as an alternative to the traditional “G-Frame� system. Since a mask-based system provides less rigid fixation than the G-Frame, the Icon incorporates an Intra-Fraction Motion Management (IFMM) system to monitor patient motion. The system utilizes two infrared cameras along with infrared reflectors placed on the frame mount (stationary) and at the tip of the patient’s nose (mobile). The baseline position of the patient marker relative to the stationary markers is established once the patient is set up for CBCT. When movement of the patient reflector away from the baseline position is greater than a preset tolerance (defaulted at 1.5mm), the sources are blocked. Once the patient reflector moves back within tolerance, the sources become unblocked and the treatment continues. Although some regulatory jurisdictions require a monthly quantitative assessment of the IFMM, we are unaware of a currently-available tool with which to measure it. The purpose of this work was the design of a simple tool to assess the system’s ability to accurately detect movement.

Methods: We designed a tool to move the IFMM’s patient reflector in each of the three orthogonal axes. The patient reflector is moved a set amount in each direction, and the system’s indicated movement is observed.

Results: Accepting the inherent noise of the system (~0.05mm), we have found the tool to be accurate to within 0.1mm versus the IFMM system.

Conclusion: This simple tool can be incorporated into a facility’s QA program in order to assess the accuracy of the system’s infrared tracking system.


Gamma Knife, Quality Assurance, Patient Movement


TH- RT Interfraction motion management : external markers-based

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