Optimizing Dose Reduction to the Left Anterior Descending Artery in Patients With Locally Advanced Lung Cancer Treated With Definitive Radiation Therapy: A Feasibility Study of Coplanar Treatments Using Double-Stacked Multileaf Collimator.

Purpose: Recent studies have shown that cardiac substructures and particularly left anterior descending artery (LAD) dose strongly correlates with the incidence of late adverse cardiac events. We evaluated whether greater cardiac and, importantly, LAD dose sparing could be achieved using a newly introduced closed bore (O-ring gantry) linac with a double-stacked multileaf collimator (Varian Ethos) relative to conventional linacs.

Methods And Materials: Twenty patients with locally advanced non-small cell lung cancer previously treated with definitive chemoradiotherapy were retrospectively evaluated. Volumetric modulated arc therapy plans were retrospectively generated for the Ethos system using optimization criteria focused on reducing overall heart and LAD doses (Heart_Ethos). Plans were also reoptimized using the same optimization criteria on a conventional C-arm linac (Heart_TB). Investigational plans were compared with the original plans and with each other using standard dose-volume histogram metrics such as percentage (V) volume receiving a specific dose (x) in Gy (Vx) or mean dose (Dmean) in Gy.

Results: Statistically significant decreases existed between the Heart_Ethos and original plans for mean heart dose (11.3 vs 14.8 Gy; < .001) and V5, V30, and V50 (63.6% vs 75.2%; < .001, 7.1% vs 12.3%; < .001, 2.1% vs 2.9%; = .03, respectively) and also for LAD mean dose (4.8 Gy vs 12.0 Gy [ < .001]) and V15 (4.9% vs 21.5%; < .001). Compared with Heart_TB, Heart_Ethos plans had significantly less mean heart dose (11.6 vs 12.2 Gy; = .006), and less heart V5 (64.4% vs 67.2%; = .049) and V30 (7.7% vs 8.8%; = .03), whereas other parameters were not significant. Optimal target coverage and other organs at risk constraints were maintained for all generated plans.

Conclusions: Heart_Ethos plans showed significant reduction in cardiac and LAD doses in comparison to the original plans while maintaining target and organ at risk goals. Our findings suggest that Ethos technology has the potential for better cardiac toxicity safety because Heart_Ethos plans were still able to reduce cardiac dose compared with Heart_TB plans.