Heavy ion RBE and microdosimetric spectra

Area of Science:

• Medical Physics
• Radiation Oncology
• Biophysics

Background:

• Accurate relative biological effectiveness (RBE) values are essential for advancing carbon beam radiation therapy.
• Clinical data for heavy ion therapy is limited, necessitating the integration of theoretical models and experimental findings.
• Neutron therapy research provides a foundational approach for determining RBE in heavy ion applications.

Purpose of the Study:

• To determine the relative biological effectiveness (RBE) for carbon ion therapy using microdosimetric measurements.
• To adapt and apply microdosimetric techniques, initially developed for neutron therapy, to heavy ion fields.
• To compare microdosimetry-derived RBE values with those from existing biophysical models.

Main Methods:

• Development of a tissue-equivalent proportional counter (TEPC) for microdosimetric measurements in heavy ion fields.
• Performance of measurements in carbon ion fields (89-430 MeV.amu-1) at the GSI, Darmstadt, near phantom surfaces and at various depths.
• Numerical evaluation of microdosimetric spectra to derive RBE values.

Main Results:

• Tentative RBE values were calculated using numerical techniques adapted from neutron therapy.
• Measurements were conducted across a range of carbon ion energies and depths within a phantom.
• Preliminary comparison of microdosimetry-derived RBE with GSI's biophysical model was performed.

Conclusions:

• Microdosimetric approaches, adapted from neutron therapy, offer a viable method for estimating RBE in carbon ion therapy.
• The preliminary findings suggest that these microdosimetric techniques can be refined for heavy ion applications.
• Further refinement of microdosimetric methods is needed to enhance their utility in clinical heavy ion radiation therapy.