Small field correction factors for the IBA Razor

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• The IBA Razor diode is a new detector for small radiation fields, intended to replace the IBA SFD.
• Its performance characteristics, particularly in small fields, require thorough investigation and quantification.

Purpose of the Study:

• To quantify the response of the IBA Razor diode in small photon fields.
• To compare the Razor diode's measurements with established dosimetry methods like air core scintillation dosimeters and Gafchromic film.
• To evaluate the impact of flattening filters and beam energy on the Razor diode's response.

Main Methods:

• Measurements were performed using photon beams from three Varian linear accelerators.
• Small fields ranging from 4mm to 30mm in width were investigated.
• The Razor diode's response was compared against an air core scintillation dosimeter (FOD) and Gafchromic film.
• Experiments were conducted with and without a flattening filter, and at two different beam energies.

Main Results:

• The IBA Razor diode exhibited an over-response, reaching up to 4.5% for fields defined by a multileaf collimator (MLC) and 7.1% for stereotactic cone-collimated fields.
• The presence of a flattening filter influenced the over-response by up to 1.5%.
• Calculated small field correction factors align with the mathematical model proposed by Liu et al. (2014).
• Variations in correction factors were observed among four Razor diode samples, suggesting a potential dependence on their accumulated dose history.

Conclusions:

• The IBA Razor diode requires specific correction factors for accurate dosimetry in small radiation fields.
• The study highlights the need to consider the detector's dose history when applying correction factors.
• Further research is warranted to fully understand and mitigate the observed over-response and dose history dependence.