Image-guided adaptive brachytherapy in cervical cancer: Patterns of relapse by brachytherapy planning parameters

Purpose: Cervical cancer patients with a bulky high-risk clinical target volume (HR-CTV) get the largest benefit of dose escalation in terms of local control. However, the expected survival benefit could be lessened by a higher metastatic risk. We examined the patterns of relapse according to major prognostic factors: the HR-CTV volume and to the D₉₀ HR-CTV. Methods and Materials: The clinical records of patients treated with pulsed-dose-rate image-guided adaptive brachytherapy after concurrent pelvic chemoradiation were reviewed. All patients had an optimal workup before treatment comprising a 18-fluorodeoxyglucose positron emission tomography/computed tomography and a para-aortic lymph node dissection. Patients with initial extrapelvic disease were excluded. Results: A total of 109 patients fulfilled inclusion criteria. Median followup was 39 months. An HR-CTV volume ≥40 cm³ was associated with a poorer local failure-free survival. There was a strong inverse correlation between the HR-CTV volume and the D₉₀ of the HR-CTV (correlation coefficient r = -0.696; p < 0.001) with increasing HR-CTV volume being associated with a decreasing D₉₀ HR-CTV. A D₉₀ HR-CTV <85 Gy and an HR-CTV volume ≥40 cm³ were significant univariate factors for experiencing nonlocal failure (p = 0.002 and 0.035, respectively), even after exclusion of local relapses. Conclusion: A lower ability to reach the target D₉₀ HR-CTV planning and an HR-CTV volume ≥ 40 cm³ correlated with a high propensity of relapsing at distance, these factors being interrelated. Next step of treatment personalization should design strategies integrating this risk, which is now the main cause of failure.