Peripheral Organ Equivalent Dose Estimation Procedure in Proton Therapy.

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Nuclear Engineering

Background:

• Proton therapy is an advanced cancer treatment that uses charged particles (protons) to deliver radiation directly to tumors.
• Accurate assessment of radiation dose to organs outside the primary treatment field is crucial for minimizing secondary cancer risks.
• Quantifying neutron and photon dose equivalents in proton therapy is essential for comprehensive patient safety evaluations.

Purpose of the Study:

• To establish a reproducible methodology for evaluating total equivalent doses in organs during proton therapy.
• To quantify neutron and photon contributions to out-of-field dose equivalents.
• To validate the methodology using a head irradiation case at iThemba Labs.

Main Methods:

• Utilized an anthropomorphic phantom with inserted photon and neutron dosimeters (TLD-600/TLD-700 pairs).
• Employed Monte Carlo simulations (GEANT code) for neutron energy distribution and Bonner sphere spectrometry for neutron spectra.
• Validated simulation results against experimental measurements for neutron spectra.

Main Results:

• Out-of-field dose equivalents within the phantom ranged from 1.4 to 0.28 mSv/Gy.
• Neutron radiation was the primary contributor to the total equivalent dose, with photons accounting for approximately 10%.
• Equivalent organ doses showed a gradual decrease with increasing distance from the target volume.

Conclusions:

• The developed methodology provides a reliable approach for assessing organ doses in proton therapy.
• Neutron dosimetry is critical for accurate total equivalent dose evaluation in proton therapy facilities.
• Results align with findings from other passive beam facilities, confirming the methodology's applicability.