Variations in the Gross Target Volume and Clinical Target Volume Evaluated by RTOG Sarcoma Radiation Oncologists for Preoperative Radiotherapy of Primary Extremity Sarcoma

Abstract

to evaluate variability in the definition of preoperative radiotherapy gross tumor volume (GTV) and clinical target volume (CTV) delineated by sarcoma radiation oncologists. Extremity sarcoma radiation planning computed tomography (CT) scans along with corresponding diagnostic MRI from 2 patients (one from lower extremity sarcoma with fused CT-MRI and one from upper extremity sarcoma without fused CT-MRI) were distributed to 10 RTOG sarcoma radiation oncologists with instructions to define GTVs and CTVs as described in the protocol RTOG 0630. The CT data with contours were then returned for central analysis. Contours representing statistically-corrected 95% (V95) and 100% (V100) agreement were computed for each structure. Minimal variations in the GTV in both lower extremity and upper extremity cases were seen among physicians; minimal variations were also noted in the lower extremity CTV, but more variability was seen for the upper extremity CTV. For GTV, the minimum, maximum, mean (SD) volumes (mL) were 673.58, 798.33, 751.72±34.58 for the lower extremity case and 383.28, 543.41, 447.25 ± 46.18 for the upper extremity case. The volume (cc) of the union, V95 and V100 were 882.14, 761.46, and 752.41 for the lower, and 587.16, 460.68, and 455.27 for the upper extremity, respectively. The overall GTV agreement was judged to be almost perfect in both lower and upper extremity cases [kappa = 0.9 (p < 0.0001) and kappa = 0.86 (p < 0.0001)]. For CTV, the minimum, maximum, mean (SD) volumes (mL) were 1145.27, 1911.49, 1604.78±210.95 for the lower extremity case and 637.27, 1245.92, 1005.57±180.45 for the upper extremity case. The volume (cc) of the union, V95 and V100 were 2093.72, 1609.23, and 1593.26 for the lower, and 1533.12, 1020.24, and 964.83 for the upper extremity cases, respectively. The overall CTV agreement was judged to be almost perfect in the lower extremity case [kappa = 0.85 (p < 0.0001)], but only substantial in the upper extremity case [kappa = 0.77 (p < 0.0001)]. Almost perfect agreement existed in the GTV of these two representative lower and upper extremity cases, regardless CT-MRI fusion status. Similarly, there was no significant disagreement in the CTV of the lower extremity, but variation in the CTV of upper extremity was seen, perhaps related to the positional differences between the planning CT and the diagnostic MRI.