Measurements of Small Field Output Correction Factors on a RefleXion Treatment Machine

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• IAEA TRS-483 provides detector response data for small fields across various treatment machines.
• Data for the novel RefleXion system's small field dosimetry is limited.
• Accurate dosimetry in small fields is crucial for modern radiotherapy techniques.

Purpose of the Study:

• To measure output correction factors for multiple detectors in small fields specifically for a clinical RefleXion unit.
• To evaluate detector performance against established dosimetry protocols like IAEA TRS-483.
• To address the unexplored dosimetry data for the RefleXion system.

Main Methods:

• Utilized a clinical RefleXion unit with a binary multi-leaf collimator and Y-jaws.
• Established reference dosimetry using the 10 × 2 cm² clinical-reference field.
• Measured detector responses (Edge, Razor, Micro-Diamond, A14SL, CC01, CC03) in small rectangular fields (1.25 × 1 to 20 × 2 cm²) at 10 cm depth.
• Employed Gafchromic EBT4 film in a solid-water phantom as the reference for calculating correction factors.

Main Results:

• Most detectors (Edge, Razor, Micro-Diamond, A14SL, CC01, CC03) showed responses within ~0.5% of film reference in 2 cm jaw fields, except at 1.25 cm width.
• Edge and Micro-Diamond showed over-response at small field widths, while CC13 exhibited volume effects.
• In 1 cm jaw fields, Edge and Micro-Diamond were close to film, but CC13 (~4%) and A14SL (~2.5%) showed significant deviations.

Conclusions:

• Small field output correction factors were determined for six detectors on the RefleXion system, following IAEA TRS-483 formalism.
• All tested detectors, except CC13, met the recommended 5% correction limit for output factor measurements.
• This study provides essential data for accurate RefleXion system dosimetry in small fields.