A modified delineation method of para‐aortic nodal clinical target volume in patients with locally advanced cervical cancer

PURPOSE: To validate the nodal center coverage (NCC) of the three mainstream delineation methods of para‐aortic nodal clinical target volume (CTV) and propose a modified delineation method of para‐aortic nodal CTV in prophylactic extended‐field irradiation (EFI) of cervical cancer. METHODS: A total of 106 patients with para‐aortic lymph nodes (PALNs) identified on PET/CT were included at Peking Union Medical College Hospital between 2011 and 2020. PALNs were classified as left lateral para‐aortic (LLPA), aorto‐caval (AC), and right para‐caval (RPC). Distances from the nodal center to the aorta and inferior vena cava (IVC) were measured. The NCC of the three mainstream delineation methods of para‐aortic nodal CTV (CTV‐K, CTV‐S, and CTV‐D) and a modified CTV (CTV‐M) was calculated. Radiotherapy plans were created based on 4 CTVs for 10 selected patients who received prophylactic EFI. The chi‐squared test and the Student's t‐test were performed. RESULTS: We identified 344 PALNs (216 LLPA, 101 AC, and 27 RPC) in 106 patients. Mean distance from the nodal center to the aorta was 9.6 mm in the LLPA and 7 mm in the AC and from the nodal center to the IVC was 5.6 mm in the AC and 5.6 mm in the RPC. CTV‐D improved the NCC of 98% compared with 92% for CTV‐K (p = 0.002) and 95% for CTV‐S (p = 0.046). CTV‐M provided the same satisfactory NCC as CTV‐D (97% vs. 98%, p = 0.485). The V(50Gy) to the duodenum, the D(mean) to the bilateral kidneys, and the V(45Gy) to the small bowel were significantly lower on the CTV‐M‐based plan than on the CTV‐D‐based plan (p = 0.001, 0.011, and 0.001, respectively). CONCLUSION: CTV‐D provided more satisfactory NCC than CTV‐K and CTV‐S. CTV‐M provided the same satisfactory NCC as CTV‐D and reduced the dose to the critical structures.