Definition of phase-space (phsp) data

A phsp is defined as a collection of representative pseudo-particles 
emerging from a radiation therapy treatment source along with their 
properties that include energy, particle type, position, direction, 
progeny and statistical weight. Every pseudo-particle in the phsp 
should be scored in such a way that it is recorded only once during 
the course of passage through the scoring surface (i.e., no further 
recording of the same particle or descendents). A phsp can take the 
form of a computer file containing the detailed description of the 
phsp particles, i.e., phsp variables as generated via a Monte-Carlo 
simulation of the treatment source, or the form of a computer code 
(event generator) which simulates the treatment source using either 
a full Monte-Carlo simulation or beam model of the radiation therapy 
source.