Dosimetry of a low-kV intra-operative X-ray source using basic analytical beam models

Area of Science:

• Medical Physics
• Radiation Dosimetry

Background:

• Low energy intra-operative X-ray sources present spatial dosimetry challenges due to rapid dose-rate changes.
• Accurate beam characterization is crucial for effective radiation therapy planning and delivery.

Purpose of the Study:

• To develop and validate an analytical model for intra-operative X-ray beams in water.
• To determine the variation of dosimetry coefficients with distance in water.
• To validate beam measurements in high-gradient dose distributions.

Main Methods:

• Utilized a basic analytical model focusing on primary beam attenuation and absorption.
• Calculated distance-dose distributions for X-ray sources.
• Compared model predictions with experimental measurements in water.

Main Results:

• The model predicts a mean mass-energy absorption coefficient change of up to 3% within clinically relevant distances.
• Calculated distance-dose distributions showed agreement with measurements within the uncertainty of the ionization chamber.
• Discrepancies emerged at larger distances where dose rates approached detector noise levels.

Conclusions:

• The analytical model provides a reliable method for predicting X-ray beam dosimetry in water for intra-operative applications.
• The model aids in validating experimental dosimetry measurements, particularly in high-gradient regions.
• Further refinement may be needed for low dose-rate regions far from the source.