Predicting Changes in Dose Distribution to Tumor and Normal Tissue When Correcting for Heterogeneity in Radiotherapy for Lung Cancer

Abstract

The purposes of this study were to examine dose alterations to gross tumor volume (GTV) and lung using heterogeneity corrections and to predict the magnitude of these changes. Three separate conformal plans were generated for 37 patients with lung cancer: plan 1 corrected for heterogeneity, plan 2 did not correct for heterogeneity, and plan 3 used identical beams and monitor units from plan 2 but with heterogeneous calculations. Plans 1 and 2 were normalized to the 95% isodose line. Mean dose (MeanDGTV), maximum dose (MaxDGTV), and minimum dose (MinDGTV) to GTV and V20 were compared between plans 1 and 3. For each patient, the amount of lung in all beam paths of plan 3 was quantified by a density correction factor and correlated with the percent change. The median percent change in MeanDGTV, MaxDGTV, and MinDGTV between plan 3 and plan 1 was -4.7% (-0.1% to -19.1%, P < 0.0001), -5.59% (0.16% to -31.86%, P < 0.0001), and -4.88% (2.90% to -24.88%, P < 0.0001), respectively. The median V20 difference was -1% (1% to -8%). The density correction factor correlated with larger differences in MeanDGTV on univariate analysis. Heterogeneity correction lowers the dose to GTV by 5%. This difference can be correlated with the density correction factor.