(Saturday, 4/4/2020) 10:30 AM - 12:30 PM [Mountain Time (GMT-6)]
Purpose: To study associations between pulmonary function tests (PFTs), lung density changes and radiation pneumonitis (RP) grades for lung cancer patients treated with definitive chemoradiotherapy.
Methods: All 137 lung cancer patients underwent 4D-CT simulation and treatment plans were prescribed to cover PTV with 60-66 Gy in 2 Gy fractions using IMRT. Planning CT images with dose distribution were mapped to follow up CT using deformable registration to assess Hounsfield Unit (HU) changes after RT. Three PFT parameters were assessed pre and post RT namely forced expiratory volume (FEV1), forced vital capacity (FVC) and diffusing capacity of the lungs for carbon monoxide (DLCO). Two Radiation oncologists graded RP using CTCAE v4.03 scale. The Spearman correlations were studied between the reduction in the PFTs with lung density changes and with RP grades.
Results: Median follow up time of 137 patients was 15 months (1-55). Grade-1 RP which is a radiological finding was traced in 39.4% whereas 24.8% harbored Grade-2 RP, and 5.1% presented with Grade-3 RP. The population average percent reductions in PFTs were FEV1 (5.8% ± 5.1%), FVC (9.8% ± 4.4%), and DLCO (19.6% ± 3.8%) after RT. Significant Spearman’s correlations were found between FEV1 change and HU increase within both lungs (r=0.533, p=0.007) and ipsilateral lung (r=0.464, p=0.022). Similar correlation was depicted for FVC change with HU increase within both lungs (r=0.554, p=0.006), ipsilateral lung (r=0.507, p=0.014), and the volume covered by V20 (r=0.509, p=0.013). DLCO decrease was also significantly correlated to HU increase in both lungs (r=0.486, p=0.035). The percent reduction for FEV1 and DLCO demonstrated significant correlations with RP grades: r=0.418, p=0.042 and r=0.790, p<0.001, respectively.
Conclusion: The reduction of FEV1, FVC, and DLCO were significantly correlated with post RT lung density changes for lung cancer. FEV1 and DLCO worsening was also correlated with radiation pneumonitis.
Funding Support, Disclosures, and Conflict of Interest: Work supported by a grant from Varian Medical Systems, Palo Alto, CA
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