A photon source model for alpha-emitter radionuclides

Area of Science:

• Nuclear physics
• Medical imaging
• Computational modeling

Background:

• Simulating Single Photon Emission Computed Tomography (SPECT) image acquisition involving alpha-emitter radionuclides presents computational challenges.
• Accurate modeling of complex radioactive decay chains is crucial for reliable SPECT simulations.

Purpose of the Study:

• To introduce the PHID (photon from Ion decay) Monte Carlo virtual source model for simulating photon emissions in alpha-emitter decay chains.
• To enhance the efficiency and accuracy of SPECT imaging simulations using alpha-emitting radionuclides.

Main Methods:

• The PHID model utilizes Geant4 databases to extract photon emission lines from decaying daughters, considering isometric transitions and atomic relaxation.
• Bateman equations are employed to calculate abundances and activities within the decay chain over a specified time range, incorporating decay rates and initial abundances.
• The model's performance is validated against analog Monte Carlo simulations and simplified source models.

Main Results:

• PHID accurately reproduces the energy and temporal distribution of photons emitted during alpha decay.
• Simulations using PHID demonstrate a significant reduction in computation time, up to 30x faster for specific setups (e.g., 1 MBq of 225Ac in water).
• Compared to simplified models for 225Ac, PHID simulates more particles and leads to higher detected counts in images (60% increase).

Conclusions:

• PHID offers an efficient and accurate method for simulating photon emission from any alpha-emitter radionuclide available in Geant4 databases.
• The model is particularly beneficial for SPECT imaging applications, improving the investigation of photon emission from alpha emitters.
• While ignoring Bremsstrahlung photons (a minor component), PHID provides a valuable, open-source tool for the research community, integrated into GATE 10.