Abstract
Introduction:To evaluate the intra-/interobserver variability of gross target volumes between delineation based on magnetic resonance imaging and computed tomography in patients simulated for stereotactic body radiotherapy for primary lung cancer and lung metastasis.Materials and Methods:Twenty-five patients (27 lesions) who underwent computed tomography and magnetic resonance simulation with the MR-60Co system (ViewRay) were included in the study. Gross target volumes were delineated on the magnetic resonance imaging (GTVMR) and computed tomography (GTVCT) images by 2 radiation oncologists (RO1 and RO2). Volumes of all contours were measured. Levels of intraobserver (GTVMR_RO vs GTVCT_RO) and interobserver (GTVMR_RO1 vs GTVMR_RO2; GTVCT_RO1 vs GTVCT_RO2) agreement were evaluated using the generalized κ statistics and the paired t test.Results:No significant volumetric difference was observed between all 4 comparisons (GTVMR_RO1 vs GTVCT_RO1, GTVMR_RO2 vs GTVCT_RO2, GTVMR_RO1 vs GTVMR_RO2, and GTVCT_RO1 vs GTVCT_RO2; P > .05), with mean volumes of GTVs ranging 5 to 6 cm3. The levels of agreement between those 4 comparisons were all substantial with mean κ values of 0.64, 0.66, 0.74, and 0.63, respectively. However, the interobserver agreement level was significantly higher for GTVCT compared to GTVMR (P <.001). The mean κ values significantly increased in all 4 comparisons for tumors >5 cm3 compared to tumors ≤5 cm3 (all P < .05).Conclusion:No significant differences in volumes between magnetic resonance- and computed tomograpghy-based Gross target volumes were found among 2 ROs. Magnetic resonance-based GTV delineation for lung stereotactic body radiotherapy also demonstrated acceptable interobserver agreement. Tumors >5 cm3 show higher intra-/interobserver agreement compared to tumors <5 cm3. More experience should be accumulated to reduce variability in magnetic resonance-based Gross target volumes delineation in lung stereotactic body radiotherapy.
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