Daily Cherenkov Imaging to Monitor for Unintended Field Overlap During Bilateral Breast Radiation Therapy.

Abstract

Incorporating Cherenkov imaging can improve radiation therapy treatment verification through both real-time monitoring and retrospective analysis of beam delivery. In bilateral breast radiation therapy, a medial gap between opposing beams is intentionally planned to avoid unwanted overlap in the midline region. We present the first in vivo analysis of Cherenkov images from bilateral breast radiation therapy. All patients were treated with a single-isocenter, 3-dimensional conformal plan using a deep-inspiration breath-hold technique. Cherenkov emissions were recorded with a ceiling-mounted camera. Optical phantom experiments were conducted to identify an appropriate imaging thresholding method. The minimum distance across the medial gap was measured using the Cherenkov imaging data for 3 patients recorded across a total of 23 treatment fractions. Analysis of the Cherenkov beam footprints demonstrated a discernible gap for all delivered fractions. The average minimum gap size computed in each of the patient treatment plans was 1.1 cm, 1.0 cm, and 2.0 cm. The average minimum gap size for each patient during radiation therapy measured with Cherenkov imaging was 1.0 ± 0.4 cm, 0.9 ± 0.2 cm, and 2.0 ± 0.6 cm, respectively. Intrapatient gap size variability is thought to be because of patient breath-hold differences across sessions. This study provides the use of Cherenkov imaging to verify the daily medial field gap in bilateral breast radiation therapy patients. Regular offline review of these images could enable direct feedback to the treatment team in cases of potential field overlap, while also reducing the need for radiochromic film or detector-based in vivo dosimetry.