Dosimetry and Toxicity Comparison of Three-Dimensional Conformal Radiation Therapy and Intensity-Modulated Radiation Therapy in Locally Advanced Lung Cancer Across a Large Statewide Quality Collaborative.

Purpose/objective(s): Use of intensity-modulated radiation therapy (IMRT) versus three-dimensional conformal external beam radiation therapy (3D-CRT) for definitive chemoradiation therapy (CRT) in locally advanced non-small cell lung cancer (LA-NSCLC) has been associated with decreased late pneumonitis, decreased high dose to the heart (itself associated with improved overall survival), and improved patient quality of life. In a statewide radiation oncology quality consortium, we sought to evaluate the impact of IMRT versus 3D-CRT treatment technique on dosimetry and toxicity.

Materials/methods: From 2012 to 2022, 1746 LA-NSCLC patients meeting inclusion criteria underwent definitive RT (90% CRT) with either 3D-CRT (n=313) or IMRT (n=1433) and were enrolled in the [quality consortium] prospective, multicenter statewide initiative. Physician reported toxicity and patient reported outcomes (PROs) were collected during treatment through 6 months after RT and compared by treatment technique. Inverse probability of treatment weighting (IPTW) was used to account for differences in prognostic factors between IMRT and 3D-CRT patients.

Results: Compared with 3D-CRT patients, IMRT patients had significantly larger PTVs (median 386 cc vs 292 cc, p<0.0001) and were more likely to have Stage IIIB disease (34.3% vs 23.0%, p<0.0001). After adjustment using IPTW, treatment with IMRT compared to 3D-CRT reduced high dose to the lung (mean V30Gy 17.9% vs 19.2%, p=0.027) and heart (proportion with V40Gy≥20% 6.4% vs 15.3% p<0.0001). In logistic regression models using IPTW, through 6 months of early follow-up there were no significant differences between 3D-CRT and IMRT in rates of grade 2+ acute esophagitis (Odds Ratio = 1.02; 95% CI=0.73,1.42; p=0.91) and grade 2+ early pneumonitis (OR = 1.62; 95% CI:0.89, 2.96; p=0.11) or in likelihood of a clinically significant decline in PROs.

Conclusion: With late follow-up ongoing, the current study supports the continued preferential use of IMRT over 3D-CRT for LA-NSCLC treatment due to improvements in heart and lung doses.