Dosimetric characterization and output verification for conical brachytherapy surface applicators. Part I. Electronic...

Area of Science:

• Medical Physics
• Radiation Oncology
• Brachytherapy

Background:

• Malignant surface lesions are traditionally treated with electron or superficial x-ray beams.
• Recent advancements in brachytherapy enable surface lesion treatment using specialized conical applicators with high dose rate (HDR) (192)Ir or electronic brachytherapy sources.
• Current dosimetry protocols inadequately address the unique characteristics of these surface applicators.

Purpose of the Study:

• To develop a unified method for output verification of surface applicators used in brachytherapy.
• To establish quality assurance and commissioning procedures for HDR electronic brachytherapy and (192)Ir sources with surface applicators.
• To independently verify dosimetric characteristics, including surface dose and depth dose distributions.

Main Methods:

• Air-kerma rate measurements were performed using an Attix Free-Air Chamber and small-volume ionization chambers for electronic brachytherapy sources.
• MCNP5 and EGSnrc Monte Carlo codes were utilized to calculate correction factors for determining absorbed dose to water at the treatment surface.
• In-phantom measurements assessed relative surface dose distributions and characteristic depth dose curves.

Main Results:

• Generated theoretical dose distributions and depth dose curves showed strong agreement with measured data.
• A novel output verification method was successfully established, enabling determination of applicator-specific dose to water at the treatment surface from measured air-kerma rates.

Conclusions:

• The developed output verification methods reduce uncertainties in dose delivery for surface brachytherapy treatments.
• Implementation of these methods enhances the precision of dose delivery, leading to improved patient care.
• This work provides a standardized approach for quality assurance of surface applicators in brachytherapy.