Determination of the optimal time for planning SAVI brachytherapy for APBI

Accelerated partial breast irradiation with high dose rate brachytherapy treats early-stage carcinoma. Strut-adjusted volume implant applicators are inserted into the cavity post-lumpectomy. For an unstable applicator, changes in distance are seen each day between struts. If an applicator is asymmetrical with no strut movement on subsequent days, then it is stable. If an asymmetrical applicator continues to change strut distances, it is unstable. Waiting for applicator stabilization improves treatment reproducibility but increases infection risk. There is currently no consensus on stability, with ranges from 24 hours (h) to 72 h. Therefore, this study aims to determine when stability is achieved.

We retrospectively reviewed 242 female breast cancer patients (2014-2022). CT was performed the same day as applicator insertion (Day 0) and repeated each treatment day. If applicators were initially asymmetrical, the distance between adjacent struts was measured, and the percentage change between the next and previous treatment day was calculated to determine how many applicators stabilized. Less than 5% change indicated stability.

On Day 0, 208 out of 242 patients (86%) had stable and symmetrical applicators that maintained stability each treatment day, and 34 out of 242 patients (14%) had applicators with asymmetrical struts. Within 24 h post-insertion, 229 out of 242 (95%) patients had stabilized applicators that maintained stability on subsequent treatment days.

Narrows previously suggested stability (24-72 h) to 24 h, leading to improved treatment efficiency and decreased infection risk as less time is needed to achieve applicator stability.