Utility of a 3-Dimensional Tiisue Site Marker in the Post-Operative Treatment of Breast Cancer Patients

Abstract

INTRODUCTION: Improvements in surgical techniques such as breast conservation, oncoplastic surgery and sentinel node biopsy have resulted in significant improvements for patients with breast cancer. In most cases, breast conservation requires post-operative radiotherapy, which can be burdensome and can cause significant complications to the breast and surrounding tissues. Recent technological advances have made it feasible to perform external beam radiation in a more targeted and accelerated fashion. However, many of these methods are not yet widely used in the breast due to the difficulty in defining the precise treatment area. The purpose of radiation is to treat the margins of the lumpectomy cavity, the most common site for recurrence. For this reason, a more precise mechanism for delineating the surgical site could potentially be helpful in treatment planning. OBJECTIVES: To determine the utility of an implantable, 3-dimensional bioabsorbable tissue site marker after intra-operative placement. METHODS AND MATERIALS: Patients were selected to have the BioZorbTM tissue marker implanted at the time of surgery (lumpectomy). Pre-operative imaging studies including mammography, ultrasound and magnetic resonance imaging (MRI) were used to determine extent of disease. Patients with breast implants or concomitant serious medical conditions were excluded. A total of eight patients were implanted and evaluated. All patients requiring adjuvant radiation therapy were referred for evaluation that included standard and 4-D CT to evaluate dose planning including respiratory motion. Multiple treatment plans were generated and compared, including standard tangent pairs, 3-D noncoplanar conformal, split arc coplanar VMAT, and a variant of split arc coplanar VMAT. All treatment protocols were in compliance with ASTRO guidelines per the NSABP B-39/RTOG 04-13 trial. RESULTS: The marker was easily identified using clinical maging, and clearly delineated the margins of the lumpectomy cavity. It allowed for 3-dimensional characterization of the borders surrounding the lumpectomy cavity, and it was easily distinguishable from the seroma, thus defining the GTV more accurately. Respiratory motion was easily tracked using the device making it possible to apply advanced radiation treatment methods such as IMRT and accelerated protocols. When compared to conventional methods of determining the GTV, use of the arker resulted in treatment volumes that were reduced by more than 50%. In appropriate patients, the marker also facilitated the use of an accelerated protocol, decreasing total treatment time from 6 weeks to 5 days. CONCLUSIONS: The utility of this 3-dimensional, bioabsorbable tissue marker was confirmed when placed into the lumpectomy site. The marker was consistently visualized without difficulty, was readily incorporated into standard and advanced dose planning methods, and had appreciable benefits when designing optimal dose treatment plans. Most notably, the PTV values were significantly decreased, and facilitated the use of advanced radiation techniques. The unique features of this marker may have significant impact on the adoption of targeted external beam radiation in an accelerated fashion as outlined by the NSABP B-39/ RTOG 04-13.