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A Head to Head Comparison of Two Commercial Phantoms Used for SRS QA

V Sarkar

V Sarkar*, L Huang , Y Huang , M Szegedi , P Rassiah-Szegedi , H Zhao , B Salter , University of Utah Huntsman Cancer Institute, Salt Lake City, UT


SU-E-T-38 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

To compare and contrast two commercial SRS QA phantoms

Both phantoms were evaluated in terms of their ease of setup as well as the time required to switch inserts for different tests. They were both used to evaluate the coincidence of the radiation and laser isocenters of a linear accelerator. End-to-end dosimetric tests were also performed using both ion chambers and films along two planes through the center of the phantoms. Since one phantom allows for multiple ion chamber orientations, a test was also performed to determine the effect of having the chamber oriented along the radiation beam axis’.

Changing inserts took 2 minutes on average for one phantom compared to 5 minutes for the other. The laser/radiation isocenter coincidence as determined from each phantom showed a maximum difference of 0.2mm. Ion chamber results were within 0.5% of the expected values when the chamber was perpendicular to the beams but measured a 3% underdose when the chamber was along the beam direction. Gamma (2%,2mm) pass rates of corresponding films were within 1% between phantoms.

The results of the corresponding tests run on both phantoms were comparable, showing that the phantoms were equivalent for the subset of SRS QA tests run here. However, the under dose observed when the chamber was parallel to the beam direction suggests that this configuration should be avoided.

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