Combined Ventilation and Perfusion Imaging Correlates With the Dosimetric Parameters of Radiation Pneumonitis in Radiation Therapy Planning for Lung Cancer

Abstract

The purpose of this study was to prospectively investigate clinical correlations between dosimetric parameters associated with radiation pneumonitis (RP) and functional lung imaging. Functional lung imaging was performed using four dimensional computed tomography (4D-CT) for ventilation imaging, single photon emission computed tomography (SPECT) for perfusion imaging, or both (V/Q-matched region). Using 4D-CT, ventilation imaging was derived from a low attenuation area according to CT numbers below different thresholds (vent-860 and -910). Perfusion imaging at the 10th, 30th, 50th, and 70th percentile perfusion levels (F10-F70) were defined as the top 10%, 30%, 50%, and 70% hyperperfused normal lung, respectively. V/Q-matched region was defined as the overlap of F10, F30, F50, or F70 with the ventilation volume vent-860 or vent-910 to yield F10, F30, F50, or F70 vent-860 or vent-910. All imaging data were incorporated into a 3D planning system to evaluate correlations between RP dosimetric parameters (where fV20 is the percentage of functional lung volume irradiated with >20 Gy, or fMLD, the mean dose administered to functional lung) and the percentage of functional lung volume. Radiation pneumonitis was evaluated using Common Terminology Criteria for Adverse Events version 4.0. Statistical significance was defined as a P value of < 0.05. Sixty patients who underwent curative radiation therapy were enrolled (48 patients for non-small cell lung cancer, and 12 patients for small cell lung cancer). Grades 1, 2, and 3 RP were observed in 16, 44, and 6 patients, respectively. Significant correlations were observed between the percentage of functional lung volume and fV20 (r = 0.4475 in vent-860 and 0.3508 in F30) or fMLD (r = 0.4701 in vent-860 and 0.3128 in F30) in patients with grade 2 or greater RP. For the combined analysis involving ventilation imaging (vent-860) and perfusion imaging (F30), F30 vent-860 results exhibited stronger correlations with fV20 and fMLD in patients with grade 2 or greater (r = 0.5509 in fV20 and 0.5320 in fMLD) and grade 3 RP (r = 0.8770 in fV20 and 0.8518 in fMLD). For the analysis of ipsilateral V/Q-matched region, although ipsilateral F30 vent-860 results exhibited moderate correlations with fV20 and fMLD in patients with grade 2 or greater RP (r = 0.3659 in fV20 and 0.3364 in fMLD), no significant correlations were observed in patients with grade 3. RP dosimetric parameters correlated significantly with functional lung imaging. Functional image-guided radiotherapy planning appears to predict risk factors for RP and may be effective in preserving functional lungs to reduce the incidence of severe RP in future.