Internal Bremsstrahlung, the missing process in beta decay Monte Carlo simulation: The relevance in ³²P...

Area of Science:

• Nuclear Medicine
• Medical Physics
• Radiation Dosimetry

Background:

• Dose Point Kernels (DPKs) are crucial for dosimetry in nuclear medicine, typically derived from Monte Carlo (MC) simulations.
• Standard DPK calculations often omit Internal Bremsstrahlung (IB), a photon emission process accompanying beta decay.
• The spectral distribution of IB photons is continuous and can influence absorbed dose calculations.

Purpose of the Study:

• To investigate the significance of Internal Bremsstrahlung (IB) emission on Dose Point Kernel (DPK) estimation for 32P.
• To quantify the contribution of IB photons to DPK values.
• To provide DPK values corrected for IB photon contributions for 32P.

Main Methods:

• DPKs were calculated using GAMOS MC simulations with and without an IB source term for 32P.
• The standard beta decay spectrum of 32P was used for initial DPK estimation (Fβ).
• A secondary MC simulation incorporated IB photons to calculate corrected DPKs (Fβ+IB), analyzing the difference (δ) as a function of radial distance (R).

Main Results:

• While beta particles dominate energy deposition at short distances, IB photons have a minor impact.
• At larger radial distances (R), DPK values including IB (Fβ+IB) were 30-40% higher than those without (Fβ).
• This indicates a significant underestimation of dose at greater distances when IB is neglected.

Conclusions:

• Incorporating Internal Bremsstrahlung (IB) into Monte Carlo simulations is recommended for accurate DPK estimation.
• The study provides DPK values corrected for IB photons, enhancing the precision of dosimetry for 32P.
• Accurate dosimetry is essential for effective radiation therapy and nuclear medicine applications.