A virtual matching technique for three-field breast irradiation using 3-D planning

Area of Science:

• Radiation Oncology
• Medical Physics
• 3D Imaging

Background:

• Breast cancer radiation therapy often uses a three-field technique for chest wall and lymph node treatment.
• Matching anterior supraclavicular fields with opposed tangent fields can be challenging.
• A single isocenter technique is not always feasible, necessitating precise field matching.

Purpose of the Study:

• To describe and validate a simple, fast, and accurate technique for estimating radiation field matching parameters.
• To utilize 3-D treatment planning software for geometric alignment in breast/chest wall radiation.
• To provide a method verifiable against patient anatomy without complex mathematical formulas.

Main Methods:

• A virtual external skin contour is created on the axial slice at the match line.
• The contour is displayed in a 3-D representation within the treatment planning software.
• Beam's eye view (BEV) is used to sequentially adjust couch and collimator angles until contour edges superimpose.

Main Results:

• The virtual external contour technique proved easy to use and provided BEV verification.
• Estimates for couch and collimator rotations were very close to those derived from published mathematical formulae.
• The method offers a practical alternative for achieving precise geometric matches in radiation therapy.

Conclusions:

• The described 3-D treatment planning software technique offers a simple, fast, and accurate approach to geometric field matching.
• This virtual contour method is easily verifiable against patient anatomy.
• It provides reliable estimates for couch and collimator angles, enhancing precision in breast cancer radiation therapy.