Background and purpose: To analyse dose-response relationships for local control of cervical cancer after MR image-guided brachytherapy (IGBT) based on dose-volume histogram parameters.
Methods and materials: The analysis includes 141 patients with cervix cancer (stages IB-IVA) treated with 45-50.4 Gy EBRT+/-cisplatin plus 4 x 7 Gy IGBT. Gross tumour volume (GTV), high risk clinical target volume (HR CTV) and intermediate risk CTV (IR CTV) were delineated and DVH parameters (D90, D100) were assessed. Doses were converted to the equivalent dose in 2 Gy (EQD2) using linear-quadratic model (alpha/beta=10 Gy). Groups of patients were formed according to tumour size at diagnosis (GTV(D)) of 2-5 cm (group 1) or >5 cm (2), with subgroups of the latter for HR CTV size at first IGBT 2-5 cm (2a) or >5 cm (2b). Dose-response dependence for local recurrence was evaluated by logit analysis.
Results: Eighteen local recurrences in the true pelvis were observed. Dose-response analyses revealed a significant effect of HR CTV D100 (p=0.02) and D90 (p=0.005). The ED50-values for tumour control were 33+/-15 Gy (D100) and 45+/-19 Gy (D90). ED90-values were 67 Gy (95% confidence interval [50;104]) and 86 Gy [77;113], respectively.
Conclusions: A significant dependence of local control on D100 and D90 for HR CTV was found. Tumour control rates of >90% can be expected at doses >67 Gy and 86 Gy, respectively.