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Image Based Mechanical Isocenter Runout Measurement

A Lukban*, I Crooks, Harold Leever Regional Cancer Center, Waterbury, CT

Presentations

(Saturday, 3/26/2022)   [Central Time (GMT-5)]

Purpose: To present a quantitative, image based method for the measurement of mechanical isocenter runout of conventional, gantry based LINACs.

Methods: A smartphone or other small digital video recording device is employed in a static position and compared to the typical method involving a non-static person's eye to view and record the position of a reference point/object (typically the end of a pointer stick or a simple dot on a sheet of paper) as it moves with a medical LINAC's gantry, collimator, and couch angles. The recorded video is displayed with magnification to provide increased precision that a non-static person's eye alone cannot provide. The magnification is determined and the coordinates of the reference point are observed and recorded versus a range of angular movements. Center of mass and average radius are calculated and corrected for magnification. The maximum distance of the recorded points from the average radius is taken as the maximum runout where the path of a perfect circle is taken as the definition of a mechanical movement with zero runout.

Results: The typical method using a person's direct, visual observation of mechanical runout lacks precision and spatial information. Methods described here provide recordable data and, in some cases, have revealed unusual discontinuities in mechanical movement which would have otherwise been undetectable.

Conclusion: The usual method of mechanical isocenter runout determination is colloquially referred to by many in the field as "the annual eye test" because of the severely observer-biased nature of the human-vision intensive, quantitative procedure. The digital video based method is fast to setup, observer independent, qualitative, reproducible, and offers increased precision.

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Keywords

Not Applicable / None Entered.

Taxonomy

IM- Other (General): Electromagnetic radiation (general)

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