Practical approach to electron beam dosimetry at extended SSD

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Dosimetry

Background:

• Accurate clinical dosimetry is crucial for effective radiotherapy.
• Electron beam dosimetry at extended source-to-surface distance (SSD) presents unique challenges.
• Standard dosimetry protocols may not fully account for output variations at non-standard SSDs.

Purpose of the Study:

• To develop a practical dosimetry approach for electron beams at extended SSD.
• To characterize electron beam output at nominal (100 cm) and extended (115 cm) SSD.
• To propose an improved method for treatment time calculations.

Main Methods:

• Measurements of relative output factors for various field sizes and energies at 100 cm and 115 cm SSD.
• Analysis of output variations with SSD, comparing to inverse square law predictions.
• Determination of an effective SSD (SSDeff) at dmax for different beam energies and field sizes.

Main Results:

• Electron beam output at extended SSD deviates from the inverse square law, particularly for lower energies and smaller fields.
• An effective SSD (SSDeff) was determined as a function of field size and beam energy.
• The proposed method provides a comprehensive approach to treatment time calculations.

Conclusions:

• The inverse square law is insufficient for accurate dosimetry at extended SSD for electron beams.
• Effective SSD (SSDeff) is a valuable parameter for correcting output variations.
• The developed dosimetry approach enhances the accuracy of treatment planning and delivery.