Evaluation of Diffusion-Weighted MRI to Differentiate Atelectasis From Lung Cancer in Radiation Therapy Planning: Locally Advanced Non-Small Cell Lung Cancer

Abstract

Purpose/Objective(s): Differentiating atelectasis from active neoplasm in lung cancer has been shown to improve radiation therapy targeting. Currently, PET is the gold standard functional imaging technique for this purpose. We evaluated the ability of diffusion-weighted MRI (DW-MRI) to differentiate atelectasis from active tumor and compared it to PET/CTbased delineation for radiation therapy planning. Materials/Methods: In this pilot study, six patients with locally advanced non-small cell lung cancer underwent DW-MRI and PET/CT prior to 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/mm. Apparent diffusion coefficient (ADC) maps were derived using all b-value DW-MRI images. Primary tumor (PT) and atelectasis (A) were contoured on ADC maps and PET/CT images. Contours were drawn in consensus by 2 radiation oncologists using commercially available treatment planning software. For each patient, the mean ADC (ADCmean), max standard uptake values (SUVmax), and mean standard uptake values (SUVmean) were measured both for PT and A. The averages of all the parameters were calculated. Differences between PT and Awere calculated for both functional imaging modalities. Paired t test was used to evaluate difference of ADCmean, SUVmax and SUVmean values between PT and A. While SUVmax is used in clinical practice, SUVmean was also used in the analysis for better comparability with mean ADC values. Results: The mean standard deviation of ADCmean over the subject population for primary tumor and atelectasis are 1269 193 mm/s (range: 996-1490 mm/s ) and 1836 236 mm/s (range: 1513-2100 mm/s), respectively. The mean SUVmax for primary tumor and atelectasis are 27.9 12.7 (range: 18.052.5) and 8.8 5.0 (range: 4.2-18.0), respectively. The mean SUVmean for primary tumor and atelectasis are 10.5 2.4 (range: 7.9-14.3) and 2.5 2.1(range: 1.3-6.7), respectively. Using paired t test, the difference between ADCmean values of PT and A is highly significant (PZ.0014). For SUVmax and SUVmean, the differences between PT and A are significant as well (PZ.019 and PZ.0017, respectively). Conclusions: Results of this pilot study demonstrate that both DW-MRI and PET/CT show significant differences between PT and A. DW MRI provides relevant functional imaging information for radiation therapy planning that needs to be investigated further. Author Disclosure: S. Saraiya: None. G. Hugo: None. K. Karki: None. K. Olsen: None. R. Groves: None. J. Ford: None. E. Weiss: E. Research Grant; NIH, Varian and Phillips Medical Systems. P. Royalty; UpToDate.