Utilizing Biology-Guided Radiotherapy for Coronary Artery Avoidance During Free-Breathing External Beam Radiation Delivery.

PURPOSE/OBJECTIVE(S) Radiation-induced cardiotoxicity is associated with the dose delivered to the coronary arteries (CA). Breath-hold and respiratory gating may help reduce CA dose in some individuals, but patients with cardiopulmonary comorbidities may not be candidates for these strategies. Biology-guided radiotherapy (BgRT) uses outgoing tumor PET emissions to deliver a tracked dose distribution to a moving target during the normal breathing cycle, which may reduce dose to sensitive structures like the CA without the need for additional motion management techniques. To understand dosimetric implications for the CA, we conducted a planning study utilizing the RefleXion X1 to develop plans for lung tumors in the biology-guided mode. MATERIALS/METHODS Right coronary artery (RCA) and left coronary artery (LCA) branches were delineated in three lung cancer patients (P1 = Left upper lung tumor, P2 = Right upper lung tumor, and P3 = Right lower lung tumor). BgRT plans were created with AAPM TG-101 50 Gy in 5-fraction protocol using a research version of the RefleXion treatment planning system (TPS), and dose-volume parameters of the heart, RCA, and LCA were analyzed. Using the Pearson correlation model, the correlation between: (1) the mean heart dose (MHD) and tumor location, (2) the MHD and RCA relationship, (3) the MHD and LCA relationship, (4) tumor-to-ipsilateral/contralateral branches and mean coronary dose were evaluated. RESULTS The BgRT-PTVs were 27.3, 14, and 66.7 cm3 for P1, P2, and P3, respectively. The average MHD was 2.15 Gy (Range: 0.48-5.03 Gy). The MHD was highly correlated with the tumor location (R = -0.99 and P = 0.037). The RCA and LCA received an average mean dose of 1.46 Gy (Range: 0.3-3.21 Gy) and 1.01 Gy (Range: 0.75-1.45 Gy), respectively. The RCA branches in P1, P2, and P3 received a low dose (1 Gy) of 0.50%, 40.70%, and 91.10%, respectively. Also, LCA branches in P1, P2, and P3 received V1 dose of 45.70%, 37.20%, and 58.00%, respectively. The LCA V15 was less than 10% in all cases, meeting the constraint recently proposed by Atkins, et al. The MHD had a correlation coefficient of 1.00 (P = 0.06) and 0.98 (P = 0.14) with mean RCA and LCA doses, respectively. There were insignificant correlations between targets-to-ipsilateral/contralateral branches and mean coronary dose. CONCLUSION Tracked dose distributions utilizing biology-guidance were associated with robust CA avoidance without the requirement for gating or breath-holding maneuvers. This observation also held for MHD, which was correlated with CA dose in this investigation. AUTHOR DISCLOSURE O.M. Oderinde: Stock Options; RefleXion Medical. T. Cornwell: Stock Options; RefleXion Medical. M. Owens: Stock Options; RefleXion Medical. S. Tian: None. X. Yang: None. K.A. Higgins: Research Grant; RefleXion Medical. Consultant; Astra Zeneca, Varian, Precisca. Advisory Board; Genetech; NRG Oncology. A. Da Silva: None. S.M. Shirvani: Employee; Sutter Health. Stock; RefleXion Medical. Stock Options; RefleXion Medical. Manage clinical, medical and scientific affairs; RefleXion Medical.