The Impact of Diffusion-Weighted MRI on the Definition of Gross Tumor Volume in Radiotherapy of Non-Small-Cell Lung Cancer.
OBJECTIVE
The study was designed to evaluate diffusion-weighted magnetic resonance imaging (DWI) vs. PET-CT of the thorax in the determination of gross tumor volume (GTV) in radiotherapy planning of non-small-cell lung cancer (NSCLC).


METHODS
Eligible patients with NSCLC who were supposed to receive definitive radio(chemo)therapy were prospectively recruited. For MRI, a respiratory gated T2-weighted sequence in axial orientation and non-gated DWI (b = 0, 800, 1,400 and apparent diffusion coefficient map [ADC]) were acquired on a 1.5 Tesla scanner. Primary tumors were delineated on FDG-PET/CT (stGTV) and DWI images (dwGTV). The definition of stGTV was based on the CT and visually adapted to the FDG-PET component if indicated (e.g., in atelectasis). For DWI, dwGTV was visually determined and adjusted for anatomical plausibility on T2w sequences. Beside a statistical comparison of stGTV and dwGTB, spatial agreement was determined with the "Hausdorff-Distance" (HD) and the "Dice Similarity Coefficient" (DSC).


RESULTS
Fifteen patients (one patient with two synchronous NSCLC) were evaluated. For 16 primary tumors with UICC stages I (n = 4), II (n = 3), IIIA (n = 2) and IIIB (n = 7) mean values for dwGTV were significantly larger than those of stGTV (76.6 ± 84.5 ml vs. 66.6 ± 75.2 ml, p<0.01). The correlation of stGTV and dwGTV was highly significant (r = 0.995, p<0.001). Yet, some considerable volume deviations between these two methods were observed (median 27.5%, range 0.4-52.1%). An acceptable agreement between dwGTV and stGTV regarding the spatial extent of primary tumors was found (average HD: 2.25 ± 0.7 mm; DC 0.68 ± 0.09).


CONCLUSIONS
The overall level of agreement between PET-CT and MRI based GTV definition is acceptable. Tumor volumes may differ considerably in single cases. DWI-derived GTVs are significantly, yet modestly, larger than their PET-CT based counterparts. Prospective studies to assess the safety and efficacy of DWI-based radiotherapy planning in NSCLC are warranted.
Department of Radiotherapy and Radiation Oncology, Saarland University Medical Center, Homburg, Germany.
Jochen
J
Fleckenstein
Department of Radiotherapy and Radiation Oncology, Saarland University Medical Center, Homburg, Germany.
Michael
M
Jelden
Department of Radiotherapy and Radiation Oncology, Saarland University Medical Center, Homburg, Germany.
Stephanie
S
Kremp
Department of Diagnostic and Interventional Radiology, Saarland University Medical Center, Homburg, Germany.
Philippe
P
Jagoda
Department of Diagnostic and Interventional Radiology, Saarland University Medical Center, Homburg, Germany.
Jonas
J
Stroeder
Department of Nuclear Medicine, Saarland University Medical Center, Homburg, Germany.
Fadi
F
Khreish
Department of Nuclear Medicine, Saarland University Medical Center, Homburg, Germany.
Samer
S
Ezziddin
Department of Nuclear Medicine, Saarland University Medical Center, Homburg, Germany.
Arno
A
Buecker
Department of Radiotherapy and Radiation Oncology, Saarland University Medical Center, Homburg, Germany.
Christian
C
Rübe
Department of Diagnostic and Interventional Radiology, Saarland University Medical Center, Homburg, Germany.
Guenther K
GK
Schneider
D000368:Aged; D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology* / Q000532:radiotherapy*; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D000072078:Positron Emission Tomography Computed Tomography; D013909:Thorax / Q000473:pathology; D047368:Tumor Burden