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 to the duodenum, the D to the bilateral kidneys, and the V 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.