Long-term Results of Multicatheter Accelerated Partial-Breast Irradiation

Abstract

Adjuvant radiation therapy has been shown to increase local control when delivered as a part of breast conservation surgery for patients with early stage disease. In an effort to expedite radiation therapy a variety of accelerated partial breast irradiation (APBI) techniques have been developed, yet there are few reports of long term outcomes. To partially address this we reviewed our experience with APBI via a multi-catheter interstitial brachytherapy (ISI) technique for patients treated before 2005. APBI began at our institution in 2003 and for several years was exclusively done via ISI. Patients treated in our clinic from February 2003 - March 2005 were reviewed. This date range was selected to allow for a minimum potential follow up period of ten years. Selection criteria for APBI at our institution predated the ASTRO consensus statement and, as such, included patients with age greater than 40 years at diagnosis, Tis-T2 (< 3cm) disease, no nodal involvement, no metastatic disease, negative surgical margins, and who underwent breast conservation surgery. We report patient and treatment characteristics as well as local-regional control and survival. One hundred consecutive patients were identified. Median age at diagnosis was 61 years. Median follow-up was 9.9 years. Tumor stages were 22 Tis, 72 T1, and 6 T2. All patients with invasive disease were N0. Invasive breast cancer subtypes were 62 ER/PR+ Her2 -, 7 ER/PR+ Her2 amplified, 1 ER/PR- Her2 amplified, 7 ER/PR/Her2-. By ASTRO APBI consensus categories: 41 were Suitable, 40 Cautionary, and 19 Unsuitable. Most patients in the Cautionary category were there due to age and/or DCIS histology while most patients in the Unsuitable category were there due to age < 50 years. ISI was performed via a free hand technique either in the operating room or via ultrasound guidance. The goal of the ISI was to encompass the surgical cavity plus a 2 cm margin. This approach used 22 catheters on average and treated a mean PTV volume of 163 dL. Mean coverage by the prescription dose of 34 Gy/10 fractions/twice daily was 95% with mean values for 1 - V150/V100 = 0.78, V150 = 53 mL, and V200 = 18 mL. Overall survival at ten years was 88% and actuarial ten-year local-regional control was 92%. There were 6 ipsilateral breast recurrences (IBR), 1 regional node recurrence (LN), 1 simultaneous IBR-LN recurrence, 1 LN and distant recurrence, and 1 distant recurrence. Fat necrosis was identified as a symptomatic event in 7 patients and as a mammogram-only finding in 13 patients. Fat necrosis was managed conservatively in 6 of the 7 symptomatic patients. Our results suggest that APBI via a multi-catheter technique in a population of predominantly Cautionary and Unsuitable patients provides durable local-regional control with limited late toxicity.