The potential for dose escalation in lung cancer as a result of systematically reducing margins used to generate planning target volume

Purpose: To determine how much the radiation dose to lung tumors could be increased as the margins used to generate planning target volume (PTV) are reduced. Methods and Materials: Treatment plans for 18 patients with non-small-cell lung carcinoma were retrospectively generated. Dose escalation was performed in two phases: The dose was increased as long as healthy tissue dose-volume constraints did not exceed (1) the values from the treatment plan originally used for the patients and (2) clinically acceptable values. Results: No correlation of dose escalation was observed with tumor location, tumor stage, tumor motion, and tumor volume. An increase in dose was observed for many of the patients with as little as 2-mm uniform reduction in PTV margin, with increases in mean PTV dose exceeding 15 Gy for 5 patients. Sixteen of 18 patients experienced a decrease in mean heart, esophagus, and lung dose when margins were reduced and prescription doses were increased. Conclusions: Reduced margins allowed an increased dose to the tumors. However, a much larger dose escalation was possible for some patients but not for others, demonstrating that each patient is different, so individual treatment plans must be tailored for maximum tumor coverage and minimum exposure of healthy tissue.