Pattern of failure after high-dose thoracic radiation for non-small cell lung cancer: the University of Michigan experience.

Purpose: Our main purpose is to study the pattern of local failure for patients with non-small cell lung cancer treated with conformal therapy.

Methods: This study included patients who failed locally and a matched group without failures after 3D conformal radiation per a radiation dose-escalation trial. Radiation doses ranged from 65.1 to 102.9 Gy in 2.1 Gy fractions, originally computed using an equivalent path length algorithm. The recurrent gross target volumes (RGTV) were contoured. The original and recurrent planning target volume (PTV and RPTV) were generated by 1 cm uniform expansion from GTV. DVHs and generalized equivalent uniform doses (EUD={Σ ( ) } ) were computed. Marginal failures were defined for RGTVs covered by the original 10 to 90 % isodose surfaces.

Results: There were no significant differences between the failed and control groups with regard to average original GTV volumes, GTV and PTV doses, and minimum PTV doses. Of the 18 RGTVs, four had marginal failure, 12 failed mostly within, and two failed outside of the original PTV. The mean EUDs were 57.1 Gy (95 % confidence interval (CI) 43.9-70.6) and 47.5 Gy (95 % CI 33.7-61.2), for the RGTVs and RPTVs, respectively, significantly below the prescribed doses (=0.03). EUDs were less than 60 Gy for 39 % of the RGTVs and 56 % of the RPTVs.

Conclusions: Recurrent tumors had significantly lower doses than the prescribed dose suggesting that some of these failures could have been avoided with modern technology such as 4D CT simulation and image-guided radiation therapy.