Introduction/Background Despite the risk of false-positive lymph nodes, FDG-PET/CT scans are increasingly used to guide treatment decisions in advanced-stage cervical cancer. The standard treatment for locally advanced cervical cancer is chemoradiotherapy. We evaluated how often standard treatment plans were modified with regard to nodal treatment (i.e. debulking, boosting and/or extended field radiotherapy) in the case of FDG-positive nodes, with the corresponding over/undertreatment rates.

Methodology Women who received chemoradiotherapy for FIGO (2009) stage IB2, IIA2-IVB cervical cancer with an FDG-positive node, between 2009–2017, were retrospectively selected from the Netherlands Cancer Registry. Patients with pathologic examination of nodes before nodal treatment were excluded.

False-positive (13–30%) and true-positive (70–87%) rates from the literature (Vermolen et al.2021) were related to the rate of patients with and without treatment modification to estimate overtreatment and undertreatment, respectively. Sensitivity analysis was performed to estimate over/undertreatment rates for patients with a higher pre-test probability of nodal metastases, using a higher PPV (94%) corresponding to an increased prevalence of nodal metastases.

Results A total of 379/435 (87%) patients had their treatment plan modified based on FDG-positive nodes, which may have resulted in undertreatment and overtreatment in 9–11% and 11–26% of patients, respectively (table 1). Treatment modification consisted mainly of nodal boosting (83%), followed by extended-field radiotherapy (62%) and debulking (12%). Sensitivity analysis slightly increased the estimated undertreatment rate from 9–11% to 12%, whereas the overtreatment rate was reduced from 11–26% to 5%.

Conclusion PET-CT had a significant impact on nodal treatment plans with modification rates of up to 87%, mainly consisting of nodal boosting. Therefore, the estimated undertreatment rate is relatively low (9–11%), while overtreatment may affect up to one quarter of patients (11–26%). The higher the likelihood of nodal metastases, the more patients will benefit from these treatment plan modifications.

Disclosures The authors have nothing to disclose besides that this work was supported by the Dutch Cancer Society [IKNL2019–12398].