Characterizing a pulse-resolved dosimetry system for complex radiotherapy beams using organic scintillators.

Area of Science:

• Medical Physics
• Radiotherapy Dosimetry
• Radiation Detection

Background:

• Accurate absorbed dose measurement is crucial in radiotherapy, especially with high spatial and temporal dose gradients.
• Existing dosimetry systems may face limitations in resolving rapid dose changes and small field characteristics.
• Advanced dosimetry is needed for quality assurance in modern, complex radiotherapy techniques.

Purpose of the Study:

• To develop and validate a fast-readout dosimetry system using fiber-coupled organic scintillators.
• To assess the system's capability for point measurements in high-gradient radiotherapy beams.
• To evaluate the system's performance in characterizing complex radiotherapy fields and transient dose events.

Main Methods:

• Development of a fiber-coupled organic scintillator dosimetry system for fast readout.
• Point measurements of absorbed dose, output factors, and percent depth doses in solid water for a 6 MV photon beam.
• Comparison of system measurements with Monte Carlo simulations for small fields (down to 0.6 cm x 0.6 cm).
• Temporal resolution assessment by measuring dose per pulse, beam start-up transients, and quality factor.

Main Results:

• The system achieved millimetre spatial resolution and measured dose per linac radiation pulse.
• Measurements of output factors and percent depth doses showed no significant differences compared to Monte Carlo simulations.
• Dose per pulse measurements demonstrated a precision of within 2.7% (1 SD) for a 10 cm x 10 cm field.
• The system successfully resolved transient dose delivery differences between Varian linac builds.

Conclusions:

• The developed fiber-coupled organic scintillator system is suitable for point measurements in radiotherapy beams with high dose gradients.
• The system shows promise for reference dosimetry and quality assurance of complex radiotherapy treatments.
• Its fast readout and high spatial resolution enable detailed characterization of linac output and beam dynamics.