The need for individualized dosimetry for tangential breast treatment

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Planning

Background:

• Individualized computer treatment plans are standard for intact breast cancer patients.
• Variability in breast shape and symmetry can impact radiation dose distribution.
• Standardizing treatment plans may offer efficiency but risks compromising dose accuracy.

Purpose of the Study:

• To evaluate the feasibility of using a library of pre-calculated treatment plans for intact breast cancer patients.
• To determine if a plan library can replace individualized computer plans without compromising treatment quality.
• To assess the potential for dose variation when using standardized plans.

Main Methods:

• Analysis of isodose distributions for 119 intact breast cancer patients treated with a 6 MV linear accelerator.
• Comparison of treatment plans using varying wedge angles (15, 30, 45 degrees), field widths, and separations.
• Evaluation of isodose coverage and dose uniformity across different patient parameters.

Main Results:

• The 30-degree wedge was optimal in 76% of cases, with other wedges yielding better plans in 24% of cases.
• Choice of wedge improved dose homogeneity by an average of 2% (range 0-7%).
• Standardized plans could lead to up to 7% underdosage in some patients due to unpredicted variations in breast shape and symmetry.

Conclusions:

• Breast shape and symmetry significantly influence dose distribution, even in patients with similar breast sizes.
• A library of standardized tangential field treatment plans for intact breasts may result in unacceptable dose variations.
• Individualized dosimetry remains essential for ensuring accurate and effective radiation therapy for intact breast cancer patients.