Variation in the gross tumor volume and clinical target volume for preoperative radiotherapy of primary large high-grade soft tissue sarcoma of the extremity among RTOG sarcoma radiation oncologists.

OBJECTIVE: To evaluate variability in the definition of preoperative radiotherapy gross tumor volume (GTV) and clinical target volume (CTV) delineated by sarcoma radiation oncologists. METHODS: Extremity sarcoma planning CT images along with the corresponding diagnostic MRI from two patients were distributed to 10 Radiation Therapy Oncology Group sarcoma radiation oncologists with instructions to define GTV and CTV using standardized guidelines. 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. RESULTS: For the GTV, the minimum, maximum, mean (SD) volumes (mL) were 674, 798, 752±35 for the lower extremity case and 383, 543, 447±46 for the upper extremity case. The volume (cc) of the union, V95 and V100 were 882, 761, and 752 for the lower, and 587, 461, and 455 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