CT-Based Quantitative Analysis of Lung COPD Phenotype Progression In Thoracic Reirradiation
Abstract
Purpose
As thoracic reirradiation becomes more common in clinical practice, the changes of underlying lung comorbidities due to multiple treatments are relatively unknown. Parametric response mapping (PRM) has shown promise as a method of tracking COPD phenotype changes due to clinical factors. This study investigates the changes in PRM-measured lung comorbidity classifications in a reirradiation cohort.
Methods
Inspiration/expiration CTs were acquired during pre-treatment simulation for 20 patients before each of their 2-3 courses of thoracic radiotherapy, which were on average 0.99 years apart. Patient scans were processed using a commercially available PRM platform, classifying lung voxels as normal, functional small airways disease (fSAD), emphysema, or parenchymal disease (PD). The percentage of each classification was reported for the overall lung volume as well as for subdivisions representing a third of each lung. The classification percentages were compared to the prior PRM timepoint, noting the lung thirds that were treated during the prior treatment.
Results
An overall decrease of normal lung classification was observed in 15 patients between their first and second treatment courses, 6 having a decrease ≥10%. Decrease in normal lung classification translated to increased fSAD, emphysema, or PD in 13, 6, and 11 patients, respectively. Increased PD was observed in the previously treated lung third in 11 patients and often resulted in a distinct region of new PD surrounding the previously treated target. Additional small decreases in normal lung classification were observed in 2 of 3 patients with 3 PRM timepoints.
Conclusion
A commercial PRM tool showed the progression of underlying lung comorbidities between courses of radiotherapy, with 6 of 20 patients showing notable conversion of normal-classified lung to abnormal classification after their first treatment course. More study is warranted to investigate the impact of reirradiation on the development of PD and progression of COPD.