Calculation of dose in asymmetric photon fields

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Treatment Planning

Background:

• Accurate calculation of monitor units (MUs) is crucial for precise radiation delivery.
• Existing methods for off-axis MU calculation may lack accuracy or simplicity.
• Asymmetric radiation fields require specialized calculation techniques.

Purpose of the Study:

• To introduce and validate a novel method for calculating monitor units (MUs) at points off the central axis.
• To compare the proposed method's accuracy against measured dose per monitor unit (DPMU) for asymmetric fields.
• To provide a simple and clinically applicable tool for radiotherapy physicists.

Main Methods:

• Development of a new algorithm for off-axis monitor unit calculation.
• Acquisition of extensive dose per monitor unit (DPMU) data for asymmetric fields.
• Comparison of calculated MUs with measured DPMU values across various linear accelerators.
• Validation of the method using parameters readily available in clinical settings.

Main Results:

• The proposed method demonstrates improved accuracy compared to existing techniques relying on large-field profile data.
• Agreement within +/- 2% was achieved between calculated and measured dose per monitor unit (DPMU).
• The method is effective for asymmetric fields generated by diverse linear accelerators.

Conclusions:

• The introduced method offers a simple and accurate approach for calculating off-axis monitor units.
• This technique enhances the precision of radiotherapy treatment planning, particularly for complex field geometries.
• Clinical implementation is facilitated by the use of readily available parameters, improving patient safety and treatment efficacy.