2408 - Retrospective Study of the Efficacy and Safety of Lung Malignancy Radiation In-Field of Prior Ipsilateral Breast Radiation

Purpose/Objective(s): The development of ipsilateral lung malignancies in patients with a prior history of breast radiation therapy is not uncommon. Given the potential for higher toxicities associated with re-irradiation, the optimal treatment for these patients is not known, and the risks of re-irradiation in patients who are not surgical candidates or who have refused surgery is not well reported in the literature. Thus, in this retrospective study we aim to formally analyze the overall efficacy and safety of re-irradiation for this unique but increasing subset of patients. Specifically, we aimed to define the efficacy and safety of re-irradiation in this context and to correlate cumulative dose exposures of nearby OARs across both courses of radiation with documented patient clinical toxicities. We hypothesize that re-irradiation will have effective local control and that higher OAR dose exposure will correlate with increased toxicities and inform discussions with patients.

Materials/Methods: This retrospective analysis includes a subset of patients at our single institution who were treated from 11/2017 through 12/2023 for a primary lung cancer vs lung metastasis ipsilateral to prior whole breast radiation. 13 patients from our network were identified. The primary endpoint of this study was local recurrence. The secondary endpoints included dosimetric data to OARs and associated late toxicities.

Results: 3 patients (23.08%) experienced chest wall necrosis (1 conventional, 1 hypofractionated, and 1 SBRT). 1 patient (7.69%) experienced grade 2 pneumonitis. Our median follow up was 36 months. 2 patients (15.38%) experienced a local recurrence at 17 and 62 months. The average Chest Wall Dmax of patients with necrosis was 10501.8 cGy, compared to 6128.57 cGy of those without. G2 necrosis patients experienced symptom resolution or stability with OTC medications. The G3 necrosis patient received hyperbaric O2 and lateral flap reconstruction. She received concurrent palbociclib and had 2 ipsilateral breast RT courses prior to lung SBRT. The G2 pneumonitis patient’s V20 was 18%. Her cough resolved after steroids. Of patients with LR, masses were located adjacent to chest wall, but adequate coverage was maintained (D95: 97.67% and 99.82%).