Expression of dose in neutron therapy.

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Neutron dosimetry often simplifies spectra into neutron and gamma components.
• Understanding the interplay between these dose components is crucial for accurate radiotherapy.
• The biological effectiveness of simultaneous neutron and gamma radiation differs from sequential exposure.

Purpose of the Study:

• To investigate the relationship between neutron and gamma dose components in clinical neutron radiotherapy.
• To model the total biological effect using the linear-quadratic (LQ) model and in vivo measured parameters.
• To compare different methods of dose expression against the biologically effective dose.

Main Methods:

• Utilized a pragmatic approach considering neutron and gamma dose components.
• Applied an extended linear-quadratic (LQ) equation to account for simultaneous dose interactions.
• Incorporated in vivo measured LQ parameters (alpha and beta) for modeling.
• Calculated equivalent neutron dose to compare physical and biological dose expressions.

Main Results:

• Total dose overestimates biologically effective dose by ~4% for every 5% gamma contamination.
• Neutron-only dose underestimates biologically effective dose by ~1.5% for every 5% gamma contamination.
• The error in underestimation (neutron dose only) is approximately three times less than the error in overestimation (total dose).

Conclusions:

• Current practices in neutron therapy (quoting total dose) can lead to significant overestimation of biological effect.
• Expressing neutron dose alone provides a more accurate, albeit underestimated, biological effect compared to total dose.
• Accurate dosimetry and biological effect assessment are critical for optimizing neutron radiotherapy outcomes.