Monte Carlo calculated detector-specific correction factors for Elekta radiosurgery cones

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Dosimetry

Background:

• Small radiation fields, crucial for stereotactic radiosurgery, present measurement challenges due to detector size and material composition.
• Clinical detectors like diodes and ion chambers exhibit response variations in small fields, necessitating accurate correction factors.
• Non-water equivalent materials in detectors lead to deviations from ideal measurements, impacting dose accuracy.

Purpose of the Study:

• To calculate correction factors for EDGE, PTW 60017 diode, and IBA CC01 ion chamber detectors.
• To assess these factors for stereotactic radiosurgery cones (5-15 mm diameters) using Monte Carlo simulations.
• To improve the accuracy of small-field radiation measurements in clinical settings.

Main Methods:

• A Monte Carlo simulation of an Elekta Synergy linear accelerator treatment head using BEAMnrc code.
• Detailed simulation of EDGE, PTW 60017, and IBA CC01 detectors using EGSnrc user codes.
• Validation of the Monte Carlo model against measured data for a 10x10 cm^2 field, including profiles and depth doses.

Main Results:

• Significant discrepancies were observed between measured and Monte Carlo calculated relative output factors (ROFs).
• EDGE and PTW 60017 diodes overestimated ROFs by up to 7.06% and 4.61%, respectively, in a 5 mm field.
• The CC01 ion chamber under-responded by up to 10%; correction factors ranged from 0.939 to 1.117 for the smallest fields.

Conclusions:

• Monte Carlo calculated correction factors are essential for accurate small-field dosimetry.
• Applying these correction factors reconciled measured ROFs with Monte Carlo calculations.
• The study provides crucial data for enhancing precision in stereotactic radiosurgery dose delivery.