Normal tissue dose and risk estimates from whole and partial breast radiation techniques

Purpose To compare radiation dose to organs at risk in patients with early‐stage breast cancer treated with lumpectomy and intraoperative radiation therapy with CT‐guided HDR brachytherapy (precision breast IORT; PB‐IORT) and those treated with external beam whole breast irradiation (WB‐DIBH) or partial breast irradiation (PB‐DIBH) with deep inspiratory breath hold. Methods We retrospectively identified 52 consecutive patients with left‐sided breast cancers treated with either PB‐IORT (n = 17, 76% outer breast) on a phase I clinical trial, adjuvant PB‐DIBH (n = 18, 56% outer breast, 6% cavity boost), or WB‐DIBH (n = 17, 76% outer breast, 53% with lumpectomy cavity boost). Conventional (2 Gy/fraction) or moderate hypofractionation (2.66 Gy/fraction) was prescribed for the external beam cohorts and 12.5 Gy in 1 fraction to 1 cm from the balloon surface was prescribed to the HDR brachytherapy cohort. CT‐based planning was used for all patients. Organ at risk doses and excess risk ratios (ERR) for secondary lung cancers, contralateral breast cancers, and cardiac toxicity were compared between treatment techniques. Results Compared to WB‐DIBH and PB‐DIBH, PB‐IORT resulted in lower ipsilateral lung V5, V10, V20, mean, and max dose (P