Proton radiobiology and its clinical implications

Area of Science:

• Radiation oncology
• Medical physics
• Radiobiology

Background:

• Proton therapy utilizes denser ionization clustering and complex DNA damage compared to X-rays.
• The relative biological effectiveness (RBE) quantifies this increased cell sterilization, with a standard clinical RBE of 1.1.
• This fixed RBE value is criticized for potentially misrepresenting late normal tissue effects and clinical X-ray energies.

Purpose of the Study:

• To evaluate the limitations of the current 1.1 RBE in proton therapy.
• To explore the necessity of organ-specific RBE adjustments for normal tissues.
• To discuss the implications of variable RBE for tumor and normal tissue dose optimization.

Main Methods:

• Analysis of existing radiobiological data and clinical practices.
• Review of mathematical models for RBE estimation based on dose, LET, and radiosensitivity.
• Consideration of normal tissue (NT) effects and dose margins in proton therapy planning.

Main Results:

• The standard 1.1 RBE may lead to normal tissue 'overdosing' or tumor 'under-dosing'.
• Variable RBE values (1.1-1.5+) are observed in specific clinical scenarios.
• Accurate RBE estimation is crucial for optimizing proton therapy safety and efficacy.

Conclusions:

• A constant 1.1 RBE is insufficient for precise proton therapy dose calculations.
• Organ-specific RBE adjustments and advanced modeling are needed.
• Multidisciplinary collaboration is essential for implementing improved proton therapy strategies.