Interstitial high-dose-rate brachytherapy in the treatment of keloids: Moving toward a volumetric approach

Abstract

Purpose: Brachytherapy (BT) after surgical resection of keloids reduces the risk of local recurrence, but standardization of dose/technique is lacking. Typical keloid BT treatment utilizes a single-channel source prescribed to 5-mm depth. We investigated the dosimetry of a volume-based target definition for interstitial high-dose-rate BT treatment of keloids.

Methods and materials: We retrospectively identified consecutive 14 patients who had a total of 20 keloids treated with interstitial high-dose-rate BT for keloids at our institution between 2004 and 2014. Keloids were treated with a single 8 Gy fraction prescribed to 5 mm beneath the scar within 36 h of surgery. Retrospectively, a 3-mm skin high-risk clinical target volume (HR-CTV) was contoured under the scar for volume-based dose calculations.

Results: Mean (SD) HR-CTV was 3.91 cm³ (3.1) and mean (SD) HR-CTV dose was 11.3 Gy (3.6). Mean D₉₀ (SD) was 62.9% (25.8) and mean V₁₀₀ (SD) was 56.5% (26.4). The mean V₁₅₀ (SD), V₂₀₀ (SD), and V₃₀₀ (SD) were as follows: 37.6% (19.9), 25.1% (14.4), and 11.3% (6.5), respectively. No local failures were reported at 9 months median followup. There were no Grade 2 or higher late toxicities.

Conclusions: Using a volume-based target definition, a wide range of target coverage was observed. This is likely a consequence of the curvature of the skin and the challenges of keeping the catheter equidistant from the skin across the target. Additional data are needed to define the potential clinical impact on outcomes/toxicities of dosimetric correlates with single-catheter BT keloid treatment.

Keywords: High-dose-rate interstitial brachytherapy; Keloids; Postoperative radiation.