A method for dose calculation for high energy photon beams based on measurements performed at reference depth

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Accurate calculation of dose per monitor unit (D/MU) is crucial for effective radiotherapy.
• Existing methods may have limitations with blocked fields or specific beam geometries.
• Dosimetry protocols recommend reference depth measurements, but some parameters require adjustments.

Purpose of the Study:

• To develop and validate a novel algorithm for calculating D/MU at any point along the beam axis.
• To account for blocked fields and variations in beam quality and geometry.
• To achieve high accuracy comparable to experimental measurements in clinical settings.

Main Methods:

• Proposed a formalism incorporating beam measurements at reference depths (5 cm or 10 cm).
• Utilized peak scatter factors, addressing challenges with parameters not directly measurable at reference depth.
• Introduced a correction factor for shielding blocks positioned close to the beam axis (< 5 cm).

Main Results:

• The algorithm accurately calculates D/MU for both blocked and unblocked fields.
• Achieved agreement better than 1% between calculated and measured doses.
• Validated across typical clinical ranges of beam qualities, source distances, and field sizes.

Conclusions:

• The proposed algorithm provides a highly accurate method for D/MU calculation in radiotherapy.
• It effectively handles complex field geometries, including those with shielding blocks.
• This formalism enhances the precision of radiation treatment planning and delivery.