Toward acquiring comprehensive radiosurgery field commissioning data using the PRESAGE/optical-CT 3D dosimetry system

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Accurate small field dosimetry is critical for radiosurgery but presents significant challenges.
• Traditional dosimetry methods can struggle with the small field sizes and complex geometries used in modern radiosurgery.

Purpose of the Study:

• To evaluate the effectiveness of PRESAGE radiochromic plastic read with optical-CT for commissioning radiosurgery fields.
• To assess the accuracy of PRESAGE in measuring total scatter factors, beam profiles, and penumbrae for small fields.

Main Methods:

• PRESAGE plastic and Gafchromic EBT film were used to measure dosimetry data for radiosurgery fields (5-40 mm) from a Novalis Tx system with a high-definition multileaf collimator (HDMLC).
• Optical-CT scanning (commercial OCTOPUS and a prototype CCD-based system) was employed for PRESAGE readout.
• Independent verification was performed using Gafchromic EBT film and mini-ion chamber/diode commissioning data.

Main Results:

• PRESAGE and EBT film measurements of total scatter factors agreed within 4% of mini-ion chamber data.
• Percent depth dose, beam profile, and penumbra measurements from PRESAGE/optical-CT systems showed good agreement with high-resolution diode data.
• The prototype optical-CT scanner achieved finer resolution (0.5 mm pixels) than previous PRESAGE applications.

Conclusions:

• PRESAGE read with optical-CT is a viable and accurate method for small field dosimetry and radiosurgery commissioning.
• The system offers significant advantages including 3D measurement capability, negligible volume averaging, and independence from beam perturbations, energy, and dose rate.