Hypoxia adapted relative biological effectiveness models for proton therapy: a simulation study.

Area of Science:

• Radiation oncology
• Medical physics
• Radiobiology

Background:

• Proton therapy currently uses a standard relative biological effectiveness (RBE) of 1.1.
• RBE and oxygenation's impact (oxygen enhancement ratio, OER) on biological effectiveness are not fully incorporated.
• RBE-OER-weighted dose (ROWD) can estimate biological effectiveness under varying oxygen levels.

Purpose of the Study:

• To compare different oxygen enhancement ratio (OER) models for calculating RBE-OER-weighted dose (ROWD).
• To investigate the consistency of ROWD estimations across various OER models.
• To assess the impact of hypoxia on proton therapy dose distribution.

Main Methods:

• Implemented and compared five OER models (WEN, TIN, STR, DAH, MEI) within a Monte Carlo simulation tool.
• Combined OER calculations with a proton RBE model and the microdosimetric kinetic model for ROWD.
• Evaluated ROWD and OER in a water phantom and a head and neck cancer case using hypoxia PET data.

Main Results:

• OER and ROWD estimates showed good agreement for WEN, MEI, and DAH models; STR and TIN yielded higher OER and lower ROWD.
• WEN, STR, and DAH models demonstrated OER-LET dependency, unlike MEI and TIN.
• All models showed reduced ROWD in hypoxic regions (OER 1.0-2.1), highlighting potential for dose optimization.

Conclusions:

• Variations exist among OER models, but all indicate significant dose differences between hypoxic and normoxic regions.
• RBE-OER weighting can guide dose escalation in hypoxic tumors or sparing of normoxic tissues.
• Accurate hypoxia imaging is crucial for implementing RBE-OER weighting in proton therapy planning.