Propensity score–based comparison of outcomes with 3D conformal radiotherapy (3D-CRT) versus intensity-modulated radiation therapy (IMRT) in treatment of esophageal cancer.

Abstract

66 Background: Although 3D-CRT is the current standard for treatment of esophageal cancers, IMRT improves dose conformality and reduces radiation exposure to normal tissue. There is no assessment of long term clinical outcomes comparing these two modalities. Methods: Between 1998-2008, 676 patients (3D-CRT=413, IMRT=263) with stage Ib-IVa (AJCC 2002 edition) esophageal cancers were treated with chemoradiation with or without surgery. To correct for potential bias inherent in observational studies, we employed inverse probability of treatment weighted (IPW) methods based on propensity scores. IPW survival plots and IPW log rank tests were used to adjust for potential bias in treatment selection. Treatment probabilities (propensity scores) were estimated using logistic regression. Results: IMRT patients were less likely to receive induction chemotherapy (35.7% vs 46.7%, p<0.01) and had poorer performance status (KPS≤80: 66.5% vs 50.0%, p<0.01). A fitted multivariate IPW-adjusted Cox model showed that overall survival was significantly associated with age (HR 1.10 for 10 years older, p=0.02), KPS (≤70 vs 90-100, HR 1.5, p=0.0002), having surgery (HR 0.56, p<0.0001), lower vs upper esophagus (HR 1.4, p=0.009), stage (3-4a vs 1-2, HR 2.6, p<0.01), and radiation modality (IMRT vs 3D-CRT, HR 0.68, p<0.0001). 3D-CRT patients had a greater risk of dying at 5 years compared to IMRT (72.6% vs 52.9%, p<0.0001) without a difference in cancer-specific mortality (Gray’s test p=0.86), time to local recurrence (p=0.27) or distant metastasis (p=0.13). Cumulative incidence of documented cardiac deaths trended higher in the 3D-CRT group (p=0.16), but most deaths were due to unknown causes (5 year estimate: 13.4% in 3D-CRT vs 4.2% in IMRT, Gray’s test p<0.0001). Analyses using propensity score as a covariate gave very similar results. Conclusions: There was a substantially higher risk of non-cancer related deaths in 3D-CRT versus IMRT. While the true cause of death cannot be determined for many 3D-CRT patients, our results suggest that improvements in radiation technology may improve treatment-related mortality in management of esophageal cancer.