The value of pre-brachytherapy MRI in aiding applicator selection for cervical cancer procedures

Brachytherapy applicator selection in the treatment of cervical cancer often relies on intra-operative judgment. Pre-brachytherapy magnetic resonance imaging (pre-MRI) may provide earlier guidance for most appropriate applicator type and size across varying vaginal canal (VC) anatomies. This study investigated the relationship between pre-MRI VC volumes and applicator selection.

One hundred and fourteen patients with cervical cancer treated with brachytherapy (2022-2024) were analyzed. Patient and treatment characteristics, including applicator type (tandem and ovoid [TO] vs. tandem and cylinder with needles [TC]), were collected. Pre-MRI with vaginal gel was used for optimal delineation of the upper 1 cm and 2 cm VC volumes, which were then analyzed in relation to applicator type and size selection.

Most patients had FIGO stage III-IV (75%) disease. The upper 2 cm VC volume was significantly associated with applicator selection across all fractions, with smaller volumes favoring TC applicators and larger volumes favoring TO applicators (p < 0.01); mean volumes were lower in the TC group than the TO group (6.48 vs. 8.06 cm³, p = 0.045).

Pre-MRI VC volume measurements may aid in applicator selection; particularly upper 2 cm volumes < 4 cm³ may require TC applicators as opposed to TO applicators. Incorporating this volume-guided approach into procedural planning can improve efficiency by facilitating upfront applicator selection and positioning. This warrants further study to determine whether stratifying applicator selection could optimize brachytherapy dosimetry and implant quality metrics associated with local control.