Dose distribution outside the target volume for 170-MeV proton beam

Area of Science:

• Medical physics
• Radiation oncology
• Particle therapy

Background:

• Dose delivered outside the primary radiation field in proton therapy can increase the risk of secondary cancer development.
• Understanding the characteristics of this out-of-field dose is crucial for patient safety.

Purpose of the Study:

• To measure and characterize the dose distribution outside the primary proton beam field.
• To investigate the contribution of different particle types and their linear energy transfer (LET) to the out-of-field dose.

Main Methods:

• Measurements were conducted using a 170-MeV proton beam at three depths along the Bragg curve.
• Passive detectors, including track etched detectors and thermoluminescence dosemeters, were employed.
• Preliminary Monte Carlo simulations were used to complement experimental measurements.

Main Results:

• The study observed an uneven decrease in dose outside the beam field, with notable local dose enhancements.
• High-energy protons (LET up to 10 keV µm⁻¹) were identified as the major contributors to the out-of-field dose.
• Both measurements and simulations confirmed the presence of particles with higher LET than initially expected.

Conclusions:

• Out-of-field dose in proton therapy is not uniformly distributed and can exhibit localized increases.
• The presence of higher LET particles outside the primary beam warrants further investigation for potential biological implications.
• These findings highlight the need for careful assessment and mitigation strategies for out-of-field dose in proton radiotherapy planning.