Reference dosimetry for light-ion beams based on graphite calorimetry.

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Hadron therapy advancements necessitate enhanced accuracy in dose delivery to target volumes.
• Current dosimetry methods based on IAEA TRS-398 for hadron beams exhibit excessive uncertainty, primarily due to beam quality correction factors (kQ).
• The mean energy to produce one ion pair in air (wair) significantly influences these correction factors and overall dose uncertainty.

Purpose of the Study:

• To investigate primary dosimetry using calorimetry as a method to reduce uncertainty in absorbed dose determination for hadron beams.
• To experimentally determine the wair value through a direct comparison between calorimetry and ionometry.
• To establish a more accurate wair value for carbon ion beams used in hadron therapy.

Main Methods:

• A graphite calorimeter was employed for primary absorbed dose determination.
• Experiments were conducted using an 80-MeV carbon ion beam.
• The wair value was derived by comparing calorimetric measurements with ionometric measurements, assuming recommended TRS-398 values for water-to-graphite stopping power ratios and ion chamber perturbation factors.

Main Results:

• Preliminary results yielded a wair value of 35.5 ± 0.9 J C⁻¹.
• This calorimetric determination offers a more direct and potentially less uncertain method for wair assessment compared to indirect methods.
• The obtained wair value contributes to refining beam quality correction factors in hadron dosimetry.

Conclusions:

• Calorimetry provides a viable primary dosimetry method for reducing uncertainty in absorbed dose measurements for hadron therapy.
• The experimentally determined wair value of 35.5 ± 0.9 J C⁻¹ can improve the accuracy of dosimetry protocols.
• Further research and validation are warranted to fully integrate calorimetric wair determination into routine hadron dosimetry practices.