Simulation-guided development of an optical calorimeter for high dose rate dosimetry

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Optical Engineering

Background:

• Optical Calorimetry (OC) measures radiation-induced refractive index changes for absorbed dose determination.
• Existing OC systems require optimization for ultra-high dose rate (UHDR) applications in radiotherapy.

Purpose of the Study:

• To optimize and characterize an OC system in software for UHDR applications.
• To build and experimentally validate a prototype OC system in a clinical setting.

Main Methods:

• Designed and simulated an OC system using optical modeling software.
• Employed image quality phantoms for noise reduction and resolution testing.
• Assessed absolute dose uncertainty in a clinical 6 MV Flattening Filter Free (FFF) photon beam across varying dose rates (0.2-6 Gy/s).

Main Results:

• Implemented design improvements: equalized pathlengths, vibration isolation, temperature control, and noise reduction algorithms.
• Simulated and experimentally confirmed increased spatial resolution (22 to 35 lp/mm) and a minimum detectable dose of 0.2 Gy.
• Observed dose rate dependent absolute dose uncertainty, decreasing from ±0.8 Gy to ±0.2 Gy at 0.2 Gy/s and 6 Gy/s, respectively.

Conclusions:

• Developed and constructed a functional OC radiation dosimeter prototype.
• The refined OC system accurately measures absorbed dose to water in a clinical photon beam.
• Reduced uncertainty at higher dose rates highlights OC's potential for UHDR radiotherapy techniques like microbeam and flash radiotherapy.