[Two approximations to obtain the collimator scatter factor (Sc) for MLC irregular fields]

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Physics

Context:

• Accurate dosimetry is crucial in high-energy X-ray radiotherapy.
• The collimator scatter factor (S(c)) accounts for scatter radiation from the collimator system.
• Current assumptions for S(c) in multileaf collimator (MLC) irregular fields may not always be accurate.

Purpose:

• To investigate the accuracy of the assumption that the collimator scatter factor for MLC irregular fields equals that of equivalent square jaw fields.
• To develop and validate a method for accurately evaluating the collimator scatter factor (S(c)(MLC)) in MLC irregular fields.
• To assess the utility of MLC irregular correction (F(MIC)) and jaw collimator correction (F(JCC)) factors for this purpose.

Summary:

• This study evaluated the collimator scatter factor (S(c)(MLC)) for multileaf collimator (MLC) irregular fields in high-energy X-ray beams (4 MV and 10 MV).
• The research found that the traditional assumption of S(c)(MLC) equaling the jaw collimator scatter factor (S(c)(jaw)) of an equivalent square field is not always valid, especially when field size ratios decrease.
• A high degree of accuracy in evaluating S(c)(MLC) was achieved using the MLC irregular correction (F(MIC)) factor or the jaw collimator correction (F(JCC)) factor.

Impact:

• Provides a more accurate method for calculating collimator scatter factors in complex radiotherapy fields.
• Enhances the precision of dose calculations in radiation therapy, particularly for non-standard field shapes.
• Contributes to improved treatment planning and delivery in cancer radiotherapy using high-energy X-rays.