MRI-guided treatment-planning optimisation in intracavitary or combined intracavitary/interstitial PDR brachytherapy using tandem ovoid applicators in locally advanced cervical cancer

Abstract Purpose To study the impact of MRI-guided treatment planning on dose/volume parameters in pulsed dose rate (PDR) brachytherapy (BT) for cervical cancer. Additionally, we investigated the potential benefit of an intracavitary/interstitial (IC/IS) modification of the classical tandem ovoid applicator. Material and methods For 24 patients we compared Standard PDR BT plans, Scaled Standard plans and MRI-guided Optimised plans. The total EBRT/BT prescribed dose to Manchester point A or to 90% of the HR-CTV (D90 HR-CTV) [1] expressed in EQD2 was 80 Gyαβ10 in 17 patients (Period I) and 84 Gyαβ10 in 7 patients (Period II). The constraints to 2 cm3 of the OAR were 90 Gyαβ3 for bladder and 75 Gyαβ3 for rectum, sigmoid and bowel. Most cases were treated with a traditional intracavitary tandem ovoid applicator. In 6 patients we used a newly designed combined IC/IS modification for the second PDR fraction and investigated the benefit of the interstitial part. Results The average gain of MRI-guided optimisation expressed in D90 HR-CTV was 4 ± 9 Gyαβ10 ( p < 0.001) and 10 ± 7 Gyαβ10 ( p = 0.003) in the two periods. The dose to 2 cm3 of the OAR met the constraints. In the group that was treated with the combined IC/IS approach, we could increase the D90 HR-CTV for the second PDR fraction with 5.4 ± 4.2 Gyαβ10 ( p = 0.005) and the D100 with 4.8 ± 3.1 Gyαβ10 ( p = 0.07). Conclusions Three-dimensional MRI-guided treatment planning and optimisation improves the DVH parameters compared to conventional planning strategies. Additional improvement can be achieved by using a combined IC/IS approach.