Use of a 3-dimensional lumpectomy marker for targeting interstitial accelerated partial breast irradiation (APBI).

Abstract

42 Background: APBI via high-dose-rate (HDR) interstitial catheter implants is an effective, highly customizable method of delivering radiotherapy in breast cancer patients. The technique is amenable to challenging anatomy such as pendulous and/or very small breasts, augmented breasts or superficial lumpectomy sites. The challenge for any APBI technique is identification of the lumpectomy cavity, which can be difficult to visualize after surgery due to post-surgical changes or tissue mobilization for oncoplastic closure. In the past we have used x-ray contrast injected into the cavity to facilitate the radiographic visualization of the cavity or individual clips. A new 3-D tissue marker (BioZorb, Focal Therapeutics, Inc.) has recently been used by surgeons to mark the area of the lumpectomy cavity at greatest risk for recurrence. In effect this acts as a communication tool to help guide the radiation oncologist for treatment planning and delivery. We examined this device for target volume localization in 15 patients receiving interstitial HDR APBI. Methods: The marker mimicking the tumor size was surgically sutured at the base of the lumpectomy cavity in 15 patients with T1T2N0N1 breast cancer with a variety of closure techniques. The clinical target volume (CTV) was taken as the 3-D outline made by the six embedded titanium markers and a 2 cm margin expanded around that structure (the planning target volume, PTV). Multiple interstitial catheters were spaced 1.5 cm apart within the PTV and 34 Gy was delivered in 10 fractions delivered over 5 treatment days. Results: The marker/CTV was easily visualized on CT images, without clips or injected contrast, making catheter insertion and planning more efficient, easier, and reproducible. The CTV volume was small (12.5 +/- 8.7cc; mean +/- SD, range 4.4–33.4cc) as was the PTV (137 +/- 60cc; mean +/- SD, range 75–327cc), relative to typical HDR APBI implants. Conclusions: The technique facilitated identification of the lumpectomy cavity in all patients treated regardless of surgical closure technique. The unambiguous margin demarcation facilitated target contouring and reproducibility for APBI.