Permanent breast seed implant dosimetry quality assurance

Area of Science:

• Oncology
• Radiation Oncology
• Medical Physics

Background:

• Accelerated partial breast irradiation (APBI) is an alternative to whole-breast irradiation for early-stage breast cancer.
• Permanent breast seed implantation is a novel APBI technique utilizing brachytherapy.
• This study evaluates dosimetric outcomes and clinical results of permanent breast seed implantation.

Purpose of the Study:

• To present pre- and post-implant dosimetric data for permanent breast seed implants.
• To correlate dosimetric data with clinical outcomes in early-stage breast cancer patients.
• To provide recommendations for establishing permanent breast seed implant programs.

Main Methods:

• Ninety-five patients with early-stage breast cancer underwent breast-conserving surgery followed by permanent seed implantation across three clinical trials.
• Planning target volume (PTV) contouring was performed using Pinnacle workstation.
• Dosimetry calculations, including dose-volume histograms (DVHs), were conducted using a Variseed planning computer.

Main Results:

• Mean pre-implant PTV coverage (V90, V100, V150, V200) was 98.8%, 97.3%, 68.8%, and 27.8%, respectively.
• Post-implant dosimetry revealed improvements in V100 (85.6% to 88.4%, p=0.004) and V200 (36.2% to 48.3%, p<0.001) due to reduced seed motion.
• Maximum skin dose was associated with skin toxicity (p=0.014).

Conclusions:

• Preplanning dosimetry targets should include V90 ≈ 100%, V100 of 95-100%, and V200 of 20-30% for optimal outcomes.
• Target volume coverage generally improved throughout seed therapy.
• Limiting maximum skin dose to 90% of prescription dose is recommended to minimize delayed skin toxicity.