Diffusion-Weighted MRI for Response Assessment During Radiation Therapy of Lung Cancer

Abstract

Diffusion-weighted MRI (DW-MRI) has recently been integrated into clinical practice to monitor tumor response to therapy in various tumor sites. However, there is only very limited data available on DW-MRI of lung cancer. The apparent diffusion coefficient (ADC), derived from DW-MRI images, is related to the mobility of water molecules and the tissue composition, including cell size, density, and integrity. In this study, changes of the ADC signal during chemoradiation therapy for lung cancer are assessed to determine the value of ADC as a predictor for response and radioresistance. Five patients with locally advanced non-small cell lung cancer (3 squamous cell cancer, 2 adenocarcinoma) underwent three series of MRI with DW-MRI and 4D CT imaging prior to, after 30 Gy, and after 60 Gy of chemoradiation therapy. Respiratory navigated DW-MRIs were acquired on a 1.5T scanner in axial planes with eight b-values ranging from 0-1000 s/mm2. Following multimodality deformable image registration, tumor (T) and affected lymph nodes (LNs) were contoured on CT, post gadolinium T1-weighted ultrafast gradient echo (VIBE), and ADC images for the purpose of comparing volumetric tumor regression and change of ADC signal with tumor response. Mean absolute ADC values and relative ADC and volume changes during radiation therapy are shown in the Table. At the end of therapy, four of five patients had partial response, and one had stable disease according to RECIST 1.1. There was no significant difference in ADC increase and VIBE or CT volume reduction between responding and non-responding patients or between tumor cell types in this small group.Oral Scientific Abstract 36; Table0 Gy0 Gy30 Gy30 Gy60 Gy60 GyTLNTLNTLNAbsolute ADC value change in m/s2 ADC (SD)1300 (423)1210 (310)1544 (388)1497 (488)1569 (469)1518 (301)ADC increase and volume decrease relative to baseline images in % ADC (SD)24 (14)22 (5)20 (9)27 (8) Volume VIBE (SD)37 (8)21 (23)60 (21)45 (29) Volume CT (SD)41 (7)14 (15)61 (6)47 (14) Open table in a new tab The preliminary results of this study show ADC signal increases early during therapy. While volume reduction continues during therapy, ADC signal does not significantly change between the 30 Gy and 60 Gy time points. Further research needs to be undertaken to investigate the predictive value of ADC signal change for tumor response, local control, and as a basis for adaptive radiation therapy planning.