Partial Breast Brachytherapy Utilizing the Single-entry, Multicatheter SAVI Device in Patients with less than 7 mm Skin-to-Cavity Distance: Favorable Acute Skin Toxicity Outcomes from a Phase II Trial

Abstract

Partial breast irradiation (PBI) offers an abbreviated, 5-day adjuvant treatment course for selected patients with early-stage breast cancer as an alternative to the standard, protracted course of whole-breast irradiation. Single-catheter balloon brachytherapy devices provide a simple means for delivering PBI and have gained wide acceptance. However, such devices may be contraindicated for treatment of tumor cavities within 7 mm of skin surface due to high radiation doses that may be delivered superficially. The multicatheter SAVI device provides a possible solution to this limitation in that its multiple-catheter design permits greater dose conformality and, potentially, greater skin sparing. This phase II study of SAVI PBI reports acute toxicity outcomes for a subset of implanted patients with less than 7 mm skin-to-cavity distance. Twenty-three patients have been accrued to a phase II trial of SAVI PBI. A subset of 12 patients was found to have less than 7 mm skin-to-cavity spacing and was selected for this analysis. All patients were diagnosed with TIS - 2N0 ductal carcinoma and negative margins. Placement of the SAVI device was performed either intraoperatively or in-office under ultrasound guidance. A total dose of 34.0 Gy in 10 twice-daily fractions was prescribed to a planning target volume (PTV) created by a 3-dimensional 1.0 cm expansion of the lumpectomy cavity. This PTV was then truncated by 5 mm from skin to limit skin dose, and a point dose constraint of 100% of the prescribed dose was assigned to the skin. Studied acute toxicities included erythema, desquamation, edema, seroma, and infection and were assessed during treatment and at 2 weeks, 1 month, and 3 months post-treatment. Toxicities were graded according to a simplified scale: 0 (none), 1 (seen on close observation), or 2 (obvious on casual observation). Follow-up for all patients ranged from 1 - 6 months. Mean dosimetric parameters were as follows: minimum dose to 90% PTV was 99.3% (range, 89.6 - 108.5%) of prescribed dose, maximum skin dose was 85.1% (range, 78.8 - 98.5%) of prescribed dose, V150 was 26.7 cc (range, 8.7 - 58.2 cc), and V200 was 12.3 cc (range, 3.6 - 30.5 cc). At 1 month post-treatment, 9 of 12 patients were noted to have Grades 1 - 2 radiation erythema which resolved in all patients followed to 3 months. No patient was noted to have dry or moist desquamation at any follow-up point. At 1 month, 8 of 12 patients were noted to have Grades 1 - 2 edema; at 3 months, 2 of 8 patients were noted to have Grade 1 edema. A SAVI permits well-tolerated PBI in patients with superficial tumor cavities and for whom single-catheter balloon brachytherapy may be technically contraindicated.