  The use of oncolytic viruses as cancer treatment has received considerable
attention in recent years, however the spatial dynamics of this viral infection
is still poorly understood. We present here a stochastic agent-based model
describing infected and uninfected cells for solid tumours, which interact with
viruses in the absence of an immune response. Two kinds of movement, namely
undirected random and pressure-driven movements, are considered: the continuum
limit of the models is derived and a systematic comparison between the systems
of partial differential equations and the individual-based model, in one and
two dimensions, is carried out.
  In the case of undirected movement, a good agreement between agent-based
simulations and the numerical and well-known analytical results for the
continuum model is possible. For pressure-driven motion, instead, we observe a
wide parameter range in which the infection of the agents remains confined to
the center of the tumour, even though the continuum model shows traveling waves
of infection; outcomes appear to be more sensitive to stochasticity and
uninfected regions appear harder to invade, giving rise to irregular,
unpredictable growth patterns.
  Our results show that the presence of spatial constraints in tumours'
microenvironments limiting free expansion has a very significant impact on
virotherapy. Outcomes for these tumours suggest a notable increase in
variability. All these aspects can have important effects when designing
individually tailored therapies where virotherapy is included.
