Association Between Lung Volume Reduction and Symptomatic Radiation Pneumonitis in Lung Cancer Patients Undergoing Definitive Concurrent Chemoradiotherapy.

[PURPOSE] This study assessed lung volume alterations during radiotherapy (RT) and their predictive value for symptomatic radiation pneumonitis (RP) in lung cancer patients undergoing definitive concurrent chemoradiotherapy (CCRT) MATERIALS AND METHODS: This retrospective study included 49 patients who underwent re-simulation four-dimensional (4D) computed tomography (CT) during RT. Lung volume was measured on the 30% phase of 4D CT at initial and re-simulation scans. Associations between volume changes and symptomatic RP were analyzed using the Mann-Whitney U test. To determine the optimal cut-off value, ROC analysis and the Youden index were utilized. RP was graded based on CTCAE v5.0.

[RESULTS] Among the 49 patients, seven (14.3%) developed symptomatic RP. Dosimetric parameters did not differ significantly between patients with and without RP. However, changes in ipsilateral lung volume were significantly associated with symptomatic RP. A volume decrease >130 cm³ or a relative reduction <-7% was predictive of RP (P = .001). The area under the ROC curve for absolute change and relative change of ipsilateral lung volume were 0.905 and 0.883, respectively.

[CONCLUSION] Ipsilateral lung volume reduction during RT may serve as an early predictor of symptomatic RP, independent of traditional dosimetric factors. Monitoring volume changes with re-simulation CT could enhance RP risk assessment and guide adaptive RT planning.