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Comparing the Setup Accuracy of Non-Ionizing Patient Localization Systems with CBCT to Reduce Imaging Dose in Prone Breast Treatments

E Chung

E Chung*, T Yamamoto, J Mayadev, S Dieterich, UC Davis Medical Center, Sacramento, CA


SU-E-J-160 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: CBCT is the current gold standard to verify prone breast patient setup. We investigated in a phantom if non-ionizing localization systems can replace ionizing localization systems for prone breast treatments.

Methods: An anthropomorphic phantom was positioned on a prone breast board. Electromagnetic transponders were attached on the left chest surface. The CT images of the phantom were imported to the treatment planning system. The isocenter was set to the center of the transponders. The positions of the isocenter and transponders transferred to the transponder tracking system. The posterior phantom surface was contoured and exported to the optical surface tracking system. A CBCT was taken for the initial setup alignment on the treatment machine. Using the electromagnetic and optical localization systems, the deviation of the phantom setup from the original CT images was measured. This was compared with the difference between the original CT and kV-CBCT images.

Results: For the electromagnetic localization system, the phantom position deviated from the original CT in 1.5 mm, 0.0 mm and 0.5 mm in the anterior-posterior (AP), superior-inferior (SI) and left-right (LR) directions. For the optical localization system, the phantom position deviated from the original CT in 2.0 mm, -2.0 mm and 0.1 mm in the AP, SI and LR directions. For the CBCT, the phantom position deviated from the original CT in 4.0 mm, 1.0 mm and -1.0 mm in the AP, SI and LR directions. The measured values from the non-ionizing localization systems differed from those with the CBCT less than 3.0 mm in all directions.

Conclusions: This phantom study showed the feasibility of using a combination of non-ionizing localization systems to achieve a similar setup accuracy as CBCT for prone breast patients. This could potentially eliminate imaging dose. As a next step, we are expanding this study to actual patients.

Funding Support, Disclosures, and Conflict of Interest: This work has been in part supported by Departmental Research Award RODEPT1-JS001, Department of Radiation Oncology, UC Davis Medical Center.

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