CT-guided multi-catheter insertion technique for partial breast brachytherapy: reliable target coverage and dose homogeneity.

PURPOSE: To evaluate the feasibility and dosimetric reliability of a CT-guided method of catheter insertion for accelerated partial breast brachytherapy (APBB).
MATERIALS AND METHODS: From 1995 to 2002, 77 patients were treated with APBB using a multi-catheter low-dose-rate or high-dose-rate approach. Within that timeframe, 29 patients with early stage invasive breast cancer were treated with high-dose-rate partial breast brachytherapy and had CT scans of the brachytherapy implant available for analysis. Initially, catheter insertion was accomplished in the operating room at the time of lumpectomy using standard free-hand insertion techniques under fluoroscopic guidance and subsequent orthogonal film dosimetry. To improve the efficiency and quality of the technique, the procedure was moved to the departmental CT-simulation suite where the catheters were placed with CT guidance. Basic guidelines of needle insertion and implant construction were followed to assure appropriate intercatheter and interplanar spacing that allowed optimal dosimetric coverage of the target volume. Target volumes were delineated and a treatment plan generated using a 3D planning system (Varian Brachyvision). PTV 1 cm was defined as the lumpectomy cavity plus 1 cm and PTV 2 cm as the lumpectomy cavity plus 2 cm. Target coverage goals were set as delivery of 100% of the prescribed dose to >95% of PTV 1 cm and >90% of the dose to >90% of PTV 2 cm. Dose homogeneity index (DHI) was defined as (V150%-V100%/V100%) with a goal of achieving >0.75. Fifteen patients were treated using the initial method and 14 patients using the CT-guided technique. Targets were retrospectively entered in the initial group and dose volume histogram analysis completed on all patients. The ability of each technique to achieve the target coverage and homogeneity goals was compared.
RESULTS: With the change from traditional techniques to a CT-guided technique, the percentage of patients satisfying all dosimetric goals increased from 42% to 93%. Mean dose coverage (defined as the percentage of PTV 2 cm receiving 90% of the prescribed dose) increased from 89% to 95% (p=0.007) and the mean DHI increased from 0.77 to 0.82 with the new technique (p < 0.005).
CONCLUSIONS: Reproducible target coverage and dose homogeneity were achieved with CT-guided catheter insertion and 3D planning software. Catheters can be optimally placed with intraoperative CT evaluation and 3D planning software allows improved implant visualization resulting in optimized dosimetry. Improvements in target coverage and DHI may translate into optimized local control and improved cosmesis with a corresponding reduction in the risk of complications.