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Dosimetric Effect of Patient Arm Position in Spinal CyberKnife Robotic Radiosurgery

I Mihaylov

IB Mihaylov*, CJ Tien, JT Hepel, Rhode Island Hospital/Brown Medical Center, Providence, RI,

SU-E-T-438 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: For treatment of spine lesions with robotic CyberKnife (Accuray, Sunnvale, CA) radiosurgery, patients are simulated in the supine position with arms along the torso. Treatments often include lateral beams passing through the arms. Variation in arm position between simulation and delivery could affect delivered doses. The purpose of this work is to evaluate the potential dosimetric effect of patient extremity motion on spinal CyberKnife treatments.

Methods: Thirteen patients were selected with spinal lesions between T10 and L4. Prescription doses ranged between 1800 and 4000 cGy, delivered in 1 to 5 fractions. In addition to the treatment plan used as reference standard, a comparison plan was created with the arms contoured and contour density set to zero for each patient. This represented the extreme scenario of the patient moving their arm completely out of the field.

Results: Results: The mean difference for the minimum dose to the PTV, the maximum dose to the spinal cord, and dose to 250 cc of spinal cord are 2.4%, 4.8% and 4.5%. PTV coverage in compared plans was changed by 1.4% on average, with the coverage improved, due to less attenuation from the patient arms. As the mean arm dose relative to the prescription dose increased, the impact of removing the arms also increased.

Conclusion: The most extreme scenario of extremity motion in CyberKnife spinal radisurgery was investigated. It was found that the dosimetric impact of the arms is small. The difference in PTV coverage was 1.4%, with a difference % in minimum dose to the PTV was 2.4%. Dose differences to critical organs were within 5%. Therefore, any reasonable motion due to set-up variations and deviation from patient simulation position will be negligible.

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