Treatment planning and outcomes effects of reducing the preferred mean esophagus dose for conventionally fractionated non-small cell lung cancer radiotherapy

Abstract

Based on an analysis of published literature, our department recently lowered the preferred mean esophagus dose (MED) constraint for conventionally fractionated (2 Gy/fraction in approximately 30 fractions) treatment of locally advanced non-small cell lung cancer (LA-NSCLC) with the goal of reducing the incidence of symptomatic acute esophagitis (AE). The goal of the change was to encourage treatment planners to achieve a MED close to 21 Gy while still permitting MED to go up to the previous guideline of 34 Gy in difficult cases. We compared all our suitable LA-NSCLC patients treated with plans from one year before through one year after the constraint change. The primary endpoint for this study was achievability of the new constraint by the planners; the secondary endpoint was reduction in symptomatic AE. Planners were able to achieve the new constraint in statistically significantly more cases during the year following its explicit implementation than in the year before (P = 0.0025). Furthermore, 38% of patients treated after the new constraint developed symptomatic AE during their treatment as opposed to 48% of the patients treated before. This is a clinically desirable endpoint although the observed difference was not statistically significant. A subsequent power calculation suggests that this is due to the relatively small number of patients in the study.

Keywords: dose-volume constraints; non-small cell lung cancer; normal tissue complications probability; treatment planning.

Fig. 1

(a) The distribution of MED versus the PTV for Groups A and B. The solid line is the least‐squares fit for Group A (Rsq = 0.38). (b) Residuals (actual MED minus MED predicted by linear fit to Group A MED versus PTV) for groups A and B. Group A is well‐described by the linear fit so Group A data points are approximately equally disposed around zero. The Group B data points are displaced toward negative residuals, demonstrating the effect of the tighter MED guideline over and above effects of PTV differences in the two groups.

Fig. 2

Distribution of AE less than or ≥ Grade 2 ranked according to MED for the two groups. The vertical line is 21 Gy.

Fig. 3

Agreement between the data (in quintiles) and the acute esophagitis model (Reference 3) on which the guideline change is based. AUC refers to the area under the curve in the receiver‐operating characteristics curves for the groups described in each figure’s title.

Fig. 4

Graphical summary of differences between Groups A (before guideline change) and B (after change).