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Towards An End-To-End Test for Image-Guided Stereotactic Radiotherapy Using the ArcCHECK Phantom

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C Groh

O Sauer, C Groh*, Univ Wurzburg, Wuerzburg, Germany

SU-E-T-61 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:

To develop a reliable and fast end-to-end test for image-guided stereotactic radiotherapy using the ArcCHECK cylindrical phantom from SunNuclear. The test aims to quantify the geometric and dosimetric discrepancies with a single measurement procedure.

Methods:

A stereotactic treatment plan with eight fields, incorporating four table rotations and four gantry positions, is created on the basis of a planning CT with isocenter at the position marked on the ArcCHECK's surface. Placing the phantom at the laser isocenter and registering the cone-beam with the planning CT yields the discrepancy between the laser and kV frame. Subsequently, the phantom is moved to the determined kV-cone-beam isocenter, where the plan is delivered and cylinder and isocenter dose are measured.

Results:

The image registration using Elekta's XVI system suggested positional corrections that were in a sub-millimeter range. The dose in the isocenter was found to be within 2% of the planned dose. Comparing the measured and planned dose distribution in the cylinder using the SNC-Patient software with a gamma-criterion (1.5mm/10%; hence an emphasis on positional error) validates the agreement between kV and MV isocenter: three points failed the gamma-test. The sensitivity was evaluated by applying increasingly larger translocations of the phantom away from the isocenter, which caused the number of failed points to increase monotonically: 29 points failed for a 3mm lateral translation.

Conclusion:

The implemented test is capable of quantifying the agreement between lasers and kV isocenter, with sub-millimeter accuracy. Over that, the agreement between kV and MV isocenters could be validated. The pass rate of the gamma-criterion was well correlated to set-up errors. A bespoke analysis of the ArcCheck dose distribution is currently being implemented in order to quantify the caustic of the isocenter.

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