A novel intra pre-plan method of interstitial needle optimization for cervical cancer patients treated with Venezia applicator brachytherapy: a technical note

Purpose
Novel hybrid Venezia applicator enables intracavitary and interstitial brachytherapy (BT) for locally advanced cervical cancer. However, the method to determine the optimal interstitial needle number, position, and depth using this applicator is unknown. Therefore, we aimed to establish a method for reliable needle optimization.

Material and methods
We produced a template model of the Venezia applicator with whole needles, and acquired computed tomography (CT) images (template CT). Using this template CT as a map, clinicians could define interstitial needle’s insertion route in advance. During treatment, we first placed tandem and ovoid, and acquired a CT (tandem + ovoid CT). This was fused to the template CT by matching the contour of applicators with high accuracy. Then, we determined the optimal interstitial needle number, position, and depth to fit high-risk clinical target volume (HR-CTV) and avoid organs at risk (OARs) on the fused CT (intra pre-plan). Next, we re-inserted the tandem and ovoids with interstitial needle into patient’s uterus and vagina. We inserted the optimized interstitial needle using insertion tool of optimal depth immediately following the applicator insertion. Lastly, a real-time treatment planning CT was performed, followed by planning and treatment.

Results
We achieved a good dose distribution of Venezia applicator BT using intra pre-plan method to optimize the number of interstitial needles, position, and depth.

Conclusions
This novel intra pre-plan method of interstitial needle optimization using template CT fusion provides high reproducibility, efficiency, and safety for patients with cervical cancer treated with brachytherapy using Venezia applicator.