Intracavitary dosimetry of a high-activity remote loading device with oscillating source

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Physics

Background:

• Brachytherapy involves placing radioactive sources near tumors.
• Accurate dose distribution is crucial for effective cancer treatment.
• Fletcher applicators with Cesium-137 (137Cs) and Iridium-192 (192Ir) are used.

Purpose of the Study:

• To experimentally determine the dose distribution in water around a Fletcher applicator.
• To characterize the dosimetry of a system using 137Cs and 192Ir sources.
• To develop and validate methods for dose calculation and visualization in brachytherapy.

Main Methods:

• Dosimetric experiments using a Fletcher applicator with 137Cs and 192Ir sources.
• Measurements of dose distribution using photographic methods and an ionization chamber.
• Correction for chamber volume effects and application of the "quantisation method" for dose rate calculations.
• Development of a simple algorithm for moving 192Ir source dosimetry.
• Utilizing FORTRAN IV and CT image data for dose distribution plotting.

Main Results:

• Dose distribution was measured photographically and with an ionization chamber.
• Absolute dose rates were determined along lateral axes.
• Dose distribution was found to be spherical for angles >40° from the longitudinal axes for both 137Cs and 192Ir sources.
• A simple algorithm was proposed for the moving 192Ir source.
• Calculated dose distributions were plotted on CT images with a maximum error of 5.5%.

Conclusions:

• The study provides accurate dosimetric data for a specific brachytherapy system.
• The spherical dose distribution pattern simplifies treatment planning in certain geometries.
• The developed algorithm and visualization tools enhance treatment accuracy and clinical application.
• The findings contribute to optimizing radiotherapy techniques using 137Cs and 192Ir sources.