E Huang*, R Gonzales, B Shen, L Lin, S Alcorn, F Asrari, V Croog, S Stinson, A Walker, J Wright, Johns Hopkins University, Baltimore, MD

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  E Huang

PO-GePV-M-149 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: The ionizing radiation interacts with electronic components in the tissue expander. The displacement of tissue expander position during treatment may cause degradation of radiation treatment goal. The purpose of this study is to evaluate tissue expander position displacement during treatment using pre-treatment CBCTs.

Methods: About 10 percent of institutional breast patients receiving radiation from August 2019 to October 2020 had tissue expander in place. Sixty-three of them are included for this study. Thirty-one of cohort had Mentor Breast Tissue expander implanted and 32 had Allergan NATRELLE Tissue Expander 133 V implanted. All patients in cohort were simulated and treated at supine position. Total 33 patients (52%) underwent radiation on their left breast: 25 with active breath control (ABC) and 8 with free-breath (FB). Thirty patients (48%) received radiation to the right breast: majority of right breast group treatment delivered with FB and only 2 with ABC. The planning- CT and pre-treatment CBCTs were collected. The pre-treatment CBCTs are rigidly fused to planning-CT. The tissue expander was contoured on pre-treatment CBCT and transferred onto planning-CT. The distance of center of mass (COM) of tissue expander between CBCT and planning-CT was calculated to evaluate the displacement of its position during treatment.

Results: For cohort with Mentor, the maximum displacement was 2.88 cm and median 0.51 cm where the mean of maximum displacement was 0.61cm for ABC and 0.87cm for FB. The maximum displacement was 7.87 cm for Allergan cohort and median was 0.68cm where the mean displacement 1.57 cm with ABC and 1.3 cm with FB respectively. Forty-eight percent of Mentor cohort had displacement less than 0.5 cm while 78% of Allergan cohort showed greater than 0.5cm displacement.

Conclusion: CBCTs showed the shift of breast tissue expander in treatment delivery. Allergan expander tends to has large magnitude of displacement than Mentor.

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