Monte Carlo evaluation of kerma at a point for photon transport problems

Journal Article · Wed Jul 01 04:00:00 EDT 1987 · Med. Phys.; (United States)

DOI:https://doi.org/10.1118/1.596069· OSTI ID:5954480

Williamson, J F

Estimation of collision kerma at a geometric point arising from scattered photons is a potentially important application of Monte Carlo simulation, especially in the presence of steep flux gradients. We examine the usual method of extracting point-kerma estimates from randomly generated photon trajectories which consists of tallying the energy lost by photon collisions occurring in the vicinity of the point of interest. Several other methods derived from the equivalence of track length per unit volume and flux are evaluated as to accuracy and efficiency. Finally, a next-flight estimator is discussed in which the expected contribution of each simulated photon collision to kerma at the point of interest is calculated regardless of proximity of the collision to the point. All of these techniques are shown to involve a trade-off between statistical precision and spatial resolution: increasing the number of contributing collisions requires averaging kerma over a larger volume. Based upon both analytic models and realistic Monte Carlo simulations, use of next-flight and track-length estimators is shown to improve simulation efficiencies by factors of 2 to 20 compared to analog scoring. Practical guidelines as to choice of estimator and successful implementation are presented.

• Research Organization: Univ. of Arizona, Tucson
• OSTI ID: 5954480
• Journal Information: Med. Phys.; (United States), Journal Name: Med. Phys.; (United States) Vol. 14:4; ISSN MPHYA
• Country of Publication: United States
• Language: English

Related Subjects

654001* -- Radiation & Shielding Physics-- Radiation Physics
Shielding Calculations & Experiments
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
COLLISIONS
DOSES
ELEMENTARY PARTICLES
ENERGY
KERMA
KINETIC ENERGY
MASSLESS PARTICLES
MATHEMATICAL MODELS
MONTE CARLO METHOD
PHOTON COLLISIONS
PHOTONS
RADIATION DOSES
RECOMMENDATIONS
RESOLUTION
SPATIAL RESOLUTION