Abstract No. 19 ▪ FEATURED ABSTRACT Bronchial Artery Tc99m-MAA Injection in Patients with Pulmonary Malignancies Demonstrates Future Treatment Potential of Bronchial Y90 Radioembolization

Patients with inoperable stage III lung cancer or limited pulmonary metastatic disease are often treated with SBRT. Dose to organs at risk (OAR) limits SBRT treatment of widespread metastatic disease and central tumors. Y90-RE via the bronchial artery may present an alternative method of radiotherapy. However, potential radiation dose to tumor and OAR following bronchial Y90-RE is not known. To better understand dosimetry, we have conducted a prospective clinical trial in patients with known primary lung cancer or pulmonary metastases presenting with a history of hemoptysis for bronchial artery embolization (BAE). Patients underwent administration of Tc99m-MAA immediately prior to administration of bland-embolics. Tc99m-MAA is used as a surrogate for Y90 to assess anticipated dose to tumor as well as OAR. Patients with either primary or metastatic pulmonary malignancy presenting for BAE for secondary prophylaxis of malignancy-induced hemoptysis were eligible. After selection of the appropriate bronchial artery, 4 mCi of Tc99m-MAA was injected. Following injection, bland embolization proceeded until stasis. Subsequently, patients received a SPECT/CT of the chest and whole-body planar imaging. Patients were assessed for any adverse events. ROIs were drawn around tumor and OAR using MiM dosimetry software. Anticipated dose to tumor and OAR was calculated using TOPAS, a platform for Monte Carlo simulations. Biologically Effective Dose (BED) was calculated to estimate required activity to meet dose tolerance limits in OAR. Eight patient have been enrolled in the study. Four patients had primary NSCLC, one each with HCC, mUC, RCC, and epithelioid sarcoma. Tc99m-MAA was successfully administered in all instances, followed by standard of care bland embolization to stasis. Subsequent whole-body planar imaging and chest SPECT/CT demonstrated no non-target tracer deposition. Monte-Carlo TOPAS dosimetry analysis demonstrated that if administering Y90, Dmean BED to tumors would range from 175-2928 Gy, mean 813 Gy, while satisfying dosimetry constraints to OAR. Using Tc99m-MAA injection via the bronchial artery as a surrogate for Y90-RE in our prospective clinical trial suggests that Y90-RE could be delivered via the bronchial artery to deliver a dose to tumor comparable to or exceeding external-beam treatment goals while satisfying dosimetry constraints to OAR in patients with pulmonary malignancies. Prospective clinical evaluation of Y90-RE via the bronchial artery is warranted.