SU‐E‐T‐61: Towards An End‐To‐End Test for Image‐Guided Stereotactic Radiotherapy Using the ArcCHECK Phantom

• Published in: Medical Physics Vol. 40; no. 6; p. 217
• Main Authors: Sauer, O, Groh, C
• Format: Conference Proceeding Journal Article
• Language: English
• Published: American Association of Physicists in Medicine 01-06-2013
• Subjects: Computed tomography; Dosimetry; Image registration; Medical imaging; Radiosurgery; Surface treatments
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.4814496

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.