Investigating the Feasibility of 3D Dosimetry in the RPC IMRT H&N Phantom

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• High failure rates (~25%) in Radiologic Physics Center (RPC) credentialing highlight the need for advanced dosimetry methods.
• Current reliance on point and 2D dose measurements limits the accuracy of quality assurance in intensity-modulated radiation therapy (IMRT).

Purpose of the Study:

• To investigate the feasibility of PRESAGE/optical-CT 3D dosimetry within the RPC IMRT Head and Neck (H&N) phantom.
• To evaluate the consistency of treatment planning and delivery by comparing PRESAGE measurements with established dosimetry techniques and treatment planning system calculations.

Main Methods:

• The RPC H&N phantom was irradiated with an IMRT plan, using both standard inserts (for TLD and EBT film measurements) and PRESAGE inserts.
• 3D dose data from PRESAGE inserts were acquired using the OCTOPUS™ 5X optical-CT scanner.
• Measurements (TLD, EBT, PRESAGE) were compared against Eclipse treatment planning system calculations using dose profiles and gamma analysis (4% dose-difference, 4 mm distance-to-agreement).

Main Results:

• TLD point dose measurements showed agreement within 5% of Eclipse calculations.
• Relative dose comparisons using profiles indicated good agreement between measurements and calculations, except in steep dose gradient regions.
• Gamma comparisons demonstrated high agreement (>96%) between measurement and calculation when ignoring edge artifacts in the measurements.

Conclusions:

• The PRESAGE/optical-CT dosimetry system is a feasible and promising tool for independent dosimetry verification in the RPC IMRT H&N phantom.
• This 3D dosimetry approach has the potential to enhance IMRT quality assurance and reduce credentialing failures.