Preliminary Study on the Effect of 4DCT-Ventilation-Weighted Dose on the Radiation Induced Pneumonia Probability (RIPP)

PURPOSE: The purpose of the present study was to evaluate the feasibility of using 4-dimensional computed tomography (4DCT)-ventilation-weighted dose analysis to predict radiation-induced pneumonia probability (RIPP). METHODS AND MATERIALS: The study population for this retrospective analysis included 16 patients with stage III lung cancer. Each patient’s 4DCT images, including end-inhale and end-exhale sequences, were used for the deformable image registration, and the Hounsfield units (HU) density-change was used to calculate the ventilation. A previously established equation was used to convert the original dose (OD) D (0, i) in the lungs in the original plan (OP) to the weighted-dose (WD) D (w, i) in the weighted plan (WP). The patients were divided into 2 groups, one with radiation-induced pneumonia (RIP), and one without. The Spearman correlation analysis was used to analyze the correlation of RIP with ΔV(20) (ΔV (x) = V (w, x) in the WP – V (0, x) in the OP), ΔMLD (ΔMLD = mean lung dose (MLD) in the WP – MLD in the OP), and ΔV(5). RESULTS: The results showed that 5 of the 16 patients were suffering from acute RIP, 4 of which had higher ΔV(20) and ΔMLD values than the rest of the patients. The results of the Spearman correlation analysis for those 4 patients were as follows: RIP vs. ΔV(20), r = 0.5123; RIP vs. ΔMLD, r = 0.5119; RIP vs. ΔV(5), r = 0.1904. CONCLUSIONS: The 4DCT-ventilation-based weighted-dose analysis showed some correlation between RIPP and both ΔV(20) and ΔMLD, when comparing the weighted-dose and the conventional dose-volume histogram (DVH) analyses.