MRI-based pre-planning in patients with cervical cancer treated with three-dimensional brachytherapy.

ABSTRACT

OBJECTIVE: The aim of this study was to analyse the feasibility and determine the benefits of MRI-based pre-planning with CT/MRI data fusion in patients with cervical cancer treated with radical radiotherapy. METHODS: Patients underwent MRI examination prior to external beam radiotherapy and prior to the first and fourth fraction of brachytherapy with applicators in place. Insertion of applicators at the radiology department was performed under paracervical anaesthesia. The benefit of MRI pre-planning was determined by comparing conventional treatment planning with dose specification to "point A" and dose specification to 90% of the high-risk clinical target volume (HR-CTV D90). Tolerance of MRI evaluation with applicators, coverage of HR-CTV and dose-volume parameters for organs at risk (OAR) has been assessed in 42 brachytherapy procedures. RESULTS: Insertion of applicators at the radiology department was successful in all patients and there were no complications. The target dose was higher for MRI planning than for conventional planning (5.3 Gy vs 4.5 Gy). Maximum doses in the bladder and rectum were significantly lower (p<0.05) for MRI planning than for the conventional approach (6.49 Gy vs 7.45 Gy for bladder; 4.57 Gy vs 5.06 Gy for rectum). We found no correlation between the International Commission on Radiation Units (ICRU) point dose for OAR and the maximum dose in OAR. Nevertheless, a strong correlation between the maximum dose in OAR and the minimal dose in a volume of 2 cm(3) has been observed. CONCLUSION: MRI-based pre-planning with consecutive CT/MRI data fusion is feasible and safe, with the advantage of increasing the dose to the tumour and decreasing the dose to the organs at risk.