Implementing stereotactic accelerated partial breast irradiation using magnetic resonance guided radiation therapy

Area of Science:

• Radiation Oncology
• Medical Physics
• Oncology

Background:

• Accelerated partial breast irradiation (APBI) aims to minimize radiation exposure and treatment volume while maintaining efficacy.
• Magnetic resonance image-guided radiotherapy (MRgRT) offers superior soft-tissue contrast for precise treatment localization.
• Stereotactic body radiotherapy (SBRT) techniques allow for high-dose gradients, potentially improving therapeutic ratios.

Purpose of the Study:

• To describe the development and outcomes of an MR-guided stereotactic APBI (MRgS-APBI) program.
• To evaluate the feasibility and dosimetric outcomes of MRgS-APBI using SBRT-style regimens.
• To assess setup reproducibility and delivery efficiency in MRgS-APBI.

Main Methods:

• Two prospective non-randomized phase I/II clinical trials were conducted for MRgS-APBI (20Gyx1 and 8.5Gyx3).
• Treatment planning involved CT and MRI simulation with specialized immobilization for MR-guided setup and cine-MRI gating.
• Dosimetry data, setup errors, and cine-MRI duty cycles were collected and analyzed for 48 single-fraction and 19 three-fraction patients.

Main Results:

• 88.5% of dosimetric objectives were met across all patients, indicating potential for stricter planning targets.
• Average setup uncertainty was low at 1.0 cm ± 0.6 cm.
• The average beam-on duty cycle in the three-fraction trial was 83.0% ± 13.0%, with no treatment discontinuations due to technical issues.

Conclusions:

• MR-guided stereotactic APBI is a feasible approach for breast cancer treatment.
• The developed program and observed dosimetric outcomes provide a valuable guide for implementing MRgS-APBI at other institutions.