We investigate the potential in using of using a graphics processor unit (GPU) 
for Monte-Carlo (MC)-based radiation dose calculations. The percent depth dose 
(PDD) of photons in a medium with known absorption and scattering coefficients 
is computed using a MC simulation running on both a standard CPU and a GPU. We 
demonstrate that the GPU's capability for massive parallel processing provides a 
significant acceleration in the MC calculation, and offers a significant 
advantage for distributed stochastic simulations on a single computer. 
Harnessing this potential of GPUs will help in the early adoption of MC for 
routine planning in a clinical environment.