Inverse-probability weighted and propensity score-based analysis of long-term clinical outcomes comparing 3D conformal radiotherapy (3DCRT) with intensity-modulated radiation therapy (IMRT) in the treatment of esophageal cancer.

Abstract

e14548 Background: IMRT has clear dosimetric advantages in the sparing of normal tissues when compared to the more conventional 3DCRT technique for the treatment of esophageal cancer, but there is currently no clinical outcomes evidence to support the use of IMRT. We hypothesized that the theoretical advantages of IMRT should translate to clinical outcomes benefits compared to 3DCRT. Methods: We analyzed a cohort of 676 patients (3DCRT=413, IMRT=263) treated with chemoradiation with or without surgery between 1998-2008. To correct for potential bias inherent in observational studies, we employed inverse probability of treatment weighted (IPW) methods based on propensity scores. Treatment probabilities (propensity scores) were estimated using logistic regression. Results: IMRT patients were less likely to receive induction chemotherapy and had poorer performance status. A fitted multivariate IPW-adjusted Cox model showed that overall survival was significantly associated with age, KPS, having surgery, tumor location, stage, having PET for staging, and radiation modality. Compared to IMRT, 3DCRT patients had a significantly greater risk of dying (72.6% vs 52.9%, IPW log rank test: p<0.0001) and for local-regional recurrence (LRR) (p=0.0038). The improvement in LRR was only apparent in the non-surgically treated patients due to better tumor control in the primary site, but not in the recurrence in regional nodal sites. There was no difference in cancer-specific mortality, distant metastasis, or postoperative deaths between the two groups. An increased cumulative incidence of cardiac deaths was seen in the 3DCRT group (p=0.049), but the cause of most deaths were unknown (5 year estimate: 11.7% in 3DCRT vs 5.4% in IMRT, Gray’s test, p=0.0029). Analyses using propensity score as a covariate gave very similar results. Conclusions: Our results indicate IMRT improves treatment outcomes in the management of esophageal cancer when compared to 3DCRT. These results, while retrospective, support the use of IMRT for the treatment of esophageal cancer.