Angular dependence of detector responses in high-energy brachytherapy

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Brachytherapy

Background:

• Accurate dosimetry is crucial for effective brachytherapy treatment.
• Angular dependence of detectors can introduce uncertainties in dose measurements.
• Understanding these effects is vital for complex dose distributions.

Purpose of the Study:

• To characterize the angular dependent response of three small volume ionization chambers and a diamond detector.
• To investigate the influence of air, water, and distance on detector angular response under Ir-192 irradiation.
• To evaluate the impact of detector-specific properties and surrounding materials on angular response.

Main Methods:

• Performed Monte Carlo (MC) simulations and experimental measurements of angular dependent response in air at 10 cm.
• Conducted MC simulations under TG-43 conditions in water at various distances (1, 3, 5, 10 cm).
• Analyzed detector response relative to manufacturer-specified reference points and beam axis rotations, considering dead volumes and asymmetries.

Main Results:

• MC simulations in air were experimentally verified.
• Angular dependence was <0.5% for rotations up to 20-50 degrees in water, depending on distance.
• In air, angular dependence exceeded 0.5% at 20 degrees for microDiamond and 50 degrees for Semiflex/PinPoint; A26 showed <0.5% at all angles. Volume averaging caused up to 8% variation at 1 cm, and high-Z materials up to 4% variation.

Conclusions:

• This study provides the first investigation of perturbation factors affecting angular dependent detector response in high-energy brachytherapy dosimetry.
• Results are valuable for estimating angular response in complex dose rate distributions, such as those with multiple sources or heterogeneous environments.
• Detector-specific characteristics and surrounding materials significantly influence angular response, necessitating careful consideration in dosimetry applications.