Lung density changes after stereotactic radiotherapy: a quantitative analysis in 50 patients

Area of Science:

• Radiotherapy
• Pulmonary imaging
• Radiation oncology

Background:

• Radiologic lung density changes occur in over 50% of patients post-stereotactic body radiotherapy (SBRT) for lung cancer.
• These density changes serve as a surrogate marker for lung injury following treatment.

Purpose of the Study:

• To investigate the relationship between SBRT dose and posttreatment computed tomography (CT) density changes.
• To quantify the dose-response relationship for lung injury after SBRT.

Main Methods:

• Analysis of follow-up CT scans from Stage I lung cancer patients treated with RapidArc SBRT.
• Utilized B-spline deformable registration for coregistration of scans and voxel-Hounsfield unit histograms to analyze density changes.
• Linear mixed effects models assessed SBRT dose effects on CT density, controlling for confounders.

Main Results:

• Increased CT density showed a significant association with higher SBRT dose, larger planning target volume, and longer time post-SBRT (p < 0.0001).
• Density increases were observed in areas receiving >6 Gy, peaking in regions >20 Gy, and plateauing above 40 Gy.
• Regions receiving >36 Gy experienced up to an 18% reduction in air-filled lung fraction; no density increase was noted in the contralateral lung receiving ≥3 Gy.

Conclusions:

• A clear dose-response relationship exists between SBRT dose and quantitative CT density changes in the lung.
• A threshold for observable effect is apparent at low doses, with a plateau in density changes at higher doses.