The Quasi-Adiabatic Graphite Calorimeter for Absolute Dosimetry in Ultrahigh Dose Rate FLASH X-Ray Radiation Therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• FLASH radiotherapy utilizes ultra-high dose-rate X-rays for reduced normal tissue damage and effective tumor treatment.
• Clinical translation of FLASH radiotherapy is hindered by the lack of traceable absolute dosimetry standards for its high-energy X-ray beams.

Purpose of the Study:

• To develop a quasi-adiabatic water-controlled probe-type graphite calorimeter for absolute absorbed dose measurement in 10 MV FLASH X-ray beams.
• To establish a traceable dosimetry standard for X-ray FLASH radiotherapy to support clinical implementation.

Main Methods:

• A probe-type graphite calorimeter was engineered with thermally stabilized water for precise thermal equilibrium control of the graphite core.
• The quasi-adiabatic system was designed for accurate absolute dose measurements under ultra-high dose rate conditions.

Main Results:

• The calorimeter achieved a mean Type A relative uncertainty of less than 0.2% for single irradiations exceeding 2 Gy.
• The overall uncertainty in water-absorbed dose measurement was determined to be 1.0% (1σ), including necessary correction factors.

Conclusions:

• A functional probe-type graphite calorimeter for absolute dose measurement in 10 MV FLASH X-ray beams has been successfully developed.
• This dosimetry system addresses the critical need for traceable standards, facilitating the clinical translation of FLASH radiotherapy.