Feasibility of Left Anterior Descending Coronary Artery Sparing Radiation Therapy for Locally Advanced Lung Cancer

Purpose Efforts to mitigate radiotherapy (RT) associated cardiotoxicity have focused on constraining mean heart dose (MHD). However, recent studies have shown greater predictive power with cardiac substructure dose metrics such as the left anterior descending (LAD) coronary artery volume (V) receiving 15Gy (V15Gy) ≥10%. Herein, we investigated the feasibility of LAD radiation sparing in contemporary IMRT/VMAT lung cancer plans. Methods and Materials Single institution retrospective analysis of 54 locally advanced lung cancer patients treated with thoracic RT between February 2018-August 2021. After excluding 33 (5=non-IMRT/VMAT or intentionally LAD-optimized; 28=LAD V15Gy<10%), 21 plans with LAD V15Gy ≥10% were identified for LAD re-optimization with intent to meet LAD V15Gy <10% while maintaining meeting organ-at-risk (OAR) metrics and target coverage with original plan parameters. Dosimetric variables were compared using paired t tests. Results Most (57.1%, 12/21) were treated with definitive RT, 8/21 (38.1%) with post-operative RT, and one with neoadjuvant RT. The median prescribed RT dose was 60Gy (range 50.4-66Gy) in 30 fractions (range 28-33). LAD re-optimized plans (vs original) led to significant reductions in mean LAD V15Gy (39.4% ±13.9% vs 9.4% ±13.0%; p<0.001) and mean LAD dose (12.9Gy ± 4.6Gy vs 7.6Gy ±2.8Gy; p<0.001). Most (85.7%; 18/21) LAD re-optimized plans achieved LAD V15Gy <10%. There were no statistically significant differences in overall lung, esophageal, or spinal cord dose metrics. Only one re-optimization (1/21) exceeded an OAR constraint that was initially met in the original plan. Conclusions To our knowledge, this is the first report describing the feasibility of LAD-optimized lung cancer RT planning using the newly identified LAD V15 Gy constraint. We observed that LAD V15Gy <10% is achievable in more than 85% of plans initially exceeding this constraint, with minimal dosimetric tradeoffs. Our results support the feasibility of routine incorporation of the LAD as an OAR in modern thoracic IMRT/VMAT planning.