Determination of the Optimal Time for Planning Single-Entry Expandable Catheter Brachytherapy for APBI

Abstract

<h3>Purpose/Objective(s)</h3> APBI treats early-stage carcinoma in women using HDR with a single-entry catheter device with multiple peripheral struts inserted into the cavity post-lumpectomy. A planning CT (CT_plan) is conducted on the day of device implantation (Day 0) or the day after (Day 1). For an asymmetrical implantation, a change in distance between two struts may be seen from day to day, making the device unstable, with no consensus on when struts stabilize in patients. In this retrospective cohort study, the endpoint is the number of days between device implantation and CT_plan to achieve stability. <h3>Materials/Methods</h3> With IRB approval, we retrospectively reviewed 242 women treated with ABPI using HDR from 2014–2021. Daily CT images were reviewed in 34 patients who had qualitative strut instability and asymmetry. Instability was evaluated by superimposing the CT taken each morning to the CT_plan on the Brachytherapy Planning Software (BPS). CT data were exported to BPS, where the percent change of distance between each strut was calculated and compared to the previous day (Days 0–1, Days 1–2, etc.). The average percent change and Standard Deviation (SD) for all distances for each calendar day were determined. Struts were considered unstable if the average percent change from the previous day was greater than 5%. The information biases inherent in retrospective reviews were accounted for by ensuring no missing data. <h3>Results</h3> Strut stability, in terms of the average percent change in all strut-to-strut distances across all patients, occurs on Day 1 (24 hours after device implantation), significantly dropping from 18% (SD = 27%) to 3.6% (SD = 2.8%). Stability remained on subsequent days (Day 1 and beyond), ranging between 2–5% (Table 1). <h3>Conclusion</h3> An increase in days only results in greater strut stability after 24 hours (Days 0–1), demonstrating that waiting for more than 24 hours after device implantation to complete a CT may not be necessary for those with asymmetric and unstable struts. The implication is that this finding can aid in improving treatment efficiency and decreasing infection risk as less time is needed for the device to be inside the cavity to wait for strut stability.