ESTRO 2021 Abstract Book

S121

ESTRO 2021

Conclusion In our cohort of patients without recorded baseline cardiac admission, mean LAD dose correlates with cardiac admission post-RT and cardiac death. Cardiac admission post-RT further correlates with cardiac death. Significance of RT dose to LAD alongside cardiac admission in predicting cardiac death, may point to undiagnosed cardiac disease in this population. While hypothesis generating, our results suggest the possibility that cardiac admission post-RT and cardiac related death can be minimized by prioritizing dose reduction to LAD. OC-0192 Impact of heart irradiation on survival (OS) in lung SBRT and locally advanced NSCLC treatments. M. Fatyga 1 , J. Li 2 , J. Hu 3 , S.E. Schild 1 , J. Anderson 1 1 Mayo Clinic Arizona, Radiation Oncology, Phoenix, USA; 2 Georgia Institute of technology, School of Industrial and Systems Engineering, Atlanta, USA; 3 Arizona State University, School of Computing, Informatics, Decision Systems Engineering , Tempe, USA Purpose or Objective Recent evidence suggests that heart irradiation decreases OS in patients treated with radiation therapy (RT) for locally advanced (LA) NSCLC. Less is known about cardiac toxicity pts who receive SBRT to the lung. Materials and Methods 134 pts treated for LA-NSCLC with conventionally fractionated RT and 197 pts treated for early stage cancer with lung SBRT at Mayo Clinic Arizona were included in this study. Each group was analyzed separately. We used a multivariate Cox model Akaike Information Criterion (AIC) to select patient specific covariates predictive for OS. We integrated heart dosimetry into the Cox model using V%_D indices, for the whole heat DVH, heart digitally subdivided into 4 segments and heart digitally subdivided into 64 segments. Each model variant included previously selected patient specific covariates. We used one V%_D per model or a linear combination of V%_D indices with fused lasso operator to account for correlations among indices. We selected models in which dosimetric features were predictive for OS. Following the division into 64 segments we used a clustering algorithm to determine irradiated heart regions predictive for OS. Results 134 patients were treated for LA-NSCLC (median dose: 62Gy, 1.8-2.0 Gy/fx) and 197 pts were treated with SBRT (48Gy in 4fx and 50Gy in 5fx). High doses delivered to the right-superior region of the heart were predictive for decreased OS in LA-NSCLC patients. The best predictive index was V%_55Gy (HR = 1.04/1%, p<0.01). Low doses to the inferior region of the heart were predictive for decreased OS in SBRT patients. The most predictive index was V%_2Gy (2Gy equivalent dose, HR = 1.01/1%, p=0.01). The LA-NSCLC model applied to SBRT patients did not predict a reduction of OS because of significantly lower doses to the heart in SBRT treatments.

Table 1: Summary of predictive indices and three strategies of heart subdivision for LA-NSCLC and lung SBRT patients. Heart Subdivision Locally advanced NSCLC Lung SBRT Whole Heart DVH V%_55Gy (HR=1.04/1%, p=0.02) N/A Right-Superior Quarter DVH V%_55Gy (HR = 1.017/1%, p=0.01) N/A