SU-E-T-146: Reference Dosimetry for Protons and Light-Ion Beams Based on Graphite Calorimetry.

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Particle Therapy

Background:

• IAEA TRS-398 provides a code of practice for absorbed dose measurements using ionization chambers.
• Current methods for proton and light-ion beams have uncertainties exceeding 3.2% due to stopping power ratios and Wair values.
• Reducing uncertainty in absorbed dose measurements is crucial for precise radiation therapy.

Purpose of the Study:

• To decrease uncertainty in absorbed dose to water measurements for proton and light-ion beams.
• To quantify beam quality correction factors (kQ,Q0) using a primary standard graphite calorimeter.
• To determine dose conversion factors for deriving dose to water from graphite calorimetry.

Main Methods:

• Geant4 Monte Carlo simulations were used to calculate dose conversion factors, including water-to-graphite stopping power ratios and fluence correction factors.
• Ionization curves in graphite and water were compared to derive fluence correction factors.
• The graphite calorimeter's dose response was compared with that of ionization chambers to determine kQ,Q0.

Main Results:

• Stopping power ratios showed minimal variation (<0.35%) up to the Bragg peak.
• Fluence correction factors slightly increased above unity near the Bragg peak.
• Preliminary results for proton beams align with TRS-398 recommendations, while light-ion beams indicate higher values requiring further investigation.

Conclusions:

• The successful application of graphite calorimetry to proton, alpha, and carbon ion beams was demonstrated.
• This approach offers a promising method for reducing uncertainties in absorbed dose measurements.
• Further experimental campaigns are planned to validate and expand these findings.