Program Information
A Report From One Year Rotational Isocentricity QA for a Commercial 6D Robotic Couch with Half Circle Gantry Proton System
B Allred*, D Robertson , J Lentz , D Hernandez Morales , J Younkin , M Bues , S Keole , J Shen , Mayo Clinic Arizona, Phoenix, AZ
Presentations
SU-I-GPD-T-205 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: A 180° proton gantry paired with a 6D robotic couch provides improved patient access and cost savings compared to 360° gantries. However, this arrangement requires frequent couch isocentric rotation in order to treat both sides of the body. We present a method to evaluate the couch rotational isocentricity and report on the couch performance in three matched gantry rooms over one year.
Methods: Couch rotational isocentricity tests were performed monthly by aligning a BB to the imaging isocenter using orthogonal KV x-rays with the couch yaw at 270°. The couch was then rotated isocentrically to 5 positions in 45° steps (360°, 315°, 270°, 225°, and 180°). At each couch position, KV images were acquired and the distance between the BB image and the imaging isocenter was used to determine the couch offset. The test was performed with an empty couch and repeated with 183lbs of acrylic slabs distributed to simulate a patient’s weight. The empty couch isocentricity test was performed for 1 year; the weighted couch test was implemented later and was performed for six months. The test was also performed once using 5° couch kicks to provide higher-resolution data on the couch isocentricity.
Results: During the course of this study, the rotational isocentricity of the unweighted couch was within 0.88mm, while the weighted couch isocentricity was within 0.62mm. Moreover, the magnitude of couch offset at each angle appears to be consistent over time. The high-angular resolution data show that the couch offset increases as the couch moves away from its imaged position of 270°.
Conclusion: The monthly QA results show that the rotational isocentricity is within 1mm for all rooms and within 0.5mm for 76.3% of measurements. The addition of weights improves the couch isocentricity, which is consistent with the manufacturer commissioning measurements.
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