To evaluate the feasibility of using positron emission tomography-computed tomography (PET-CT) to guide lesion localization and radiotherapy planning for stage Ⅱ_B-IV_A cervical cancer with retroperitoneal node metastasis.

Before treatment, PET-CT was used for staging and lesion localization. Three-dimensional radiotherapy (3DRT) plans with boost doses for metastatic lymph nodes were made based on the fused PET-CT images. The obtained plans were compared with CT image-guided plans within the same period. Comparison was made by paired t test or non-parametric test.

The PET-CT plans had significantly larger GTV_nd, pGTV_nd, CTV, and PTV than the CT plans (P=0.012, 0.010, 0.018, 0.018). There were no significant differences in V₄₀, V₅₀, or D_{1 cm3} for the small intestine between the two plans (P=0.744, 0.588, 0.423). The PET-CT plans had significantly lower V₂₀, V₃₀, and D_mean for the small intestine than the CT plans (68.1% vs. 74.5%, P=0.020; 36.1% vs. 39.6%, P=0.016; 2 546.1 vs. 2 761.4 Gy, P=0.036). Moreover, the PET-CT plans had significantly larger V₂₀ and D_mean for the kidney than the CT plans (9.4% vs. 5.7%, P=0.006; 877.0 vs. 733.8 Gy, P=0.005). There were no significant differences in V₃₀ and V₄₀ for the kidney or D_mean for the rectum, bladder, colon, pelvic bone, bone marrow, and femoral head between the two plans (P=0.089, 0.341, 0.406, 0.107, 0.178, 0.397, 0.285, 0.743).

It is feasible to use fused PET-CT images to guide external 3DRT plans, which can accurately localize the metastatic lymph nodes and elevate the radiation dose. However, the protection of the small intestine and kidney should be taken into account.

Tomography, positron emission; Cervical neoplasms/three-dimensional radiotherapy; Retroperitoneal nodes metastasis