ESTRO 2025 - Abstract Book

S1417

Clinical - Lung

ESTRO 2025

showing a pseudoaneurysm of the pulmonary artery into the ipsilateral mainstem bronchus in a high dose region (Figure 1). As this pseudoaneurysm developed at a vessel/bronchus interface, a novel organ at risk (OAR) consisting of the interface between these structures is proposed. The proposed OAR is the tissue plane between the vessel and bronchus whereby an aneurysm could form called a ‘potential pseudoaneurysm plane’ (PPP). To evaluate the dosimetric characteristics of the PPP, heart (including the pulmonary artery and veins) and all central vessels were segmented. The PPP between the proximal bronchial tree, trachea, and vascular structures was generated using Boolean structure algebra. Dose characteristics of this structure were analyzed and compared to existing OAR constraints for bronchus and great vessels as defined in multi-institutional central lung SBRT trials.

Results: The PPP structure was generated in both the patient who suffered the complication as well as in additional patients treated with central SBRT (n=15). The PPP had large variations in dose from either the bronchus or vessel point max doses often previously used as dose constraints for central SBRT. For the patient suffering the G5 outcome, the D1 to the PPP in was 57Gy versus 63Gy to the bronchus. Additional patient analysis confirmed doses to PPP were often much lower (5-20Gy lower) than OAR structure limits used in our planning protocols, but lack of other bleeding events precluded statistical modeling. Conclusion: A novel critical structure definition is proposed which has significant variations from traditional bronchial or vessel dosimetric parameters. This interface structure should be considered during planning as potentially high risk and avoided when possible. Similar ‘interface’ OARs may help to predict other similar toxicities arising at organ interfaces such as fistulae or hemorrhagic complications in other body sites.

Keywords: Lung cancer, pulmonary hemorrhage, organ at risk

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