Advances in computer technology have enabled the possibility of transitioning from basic 2 - dimensional treatment planning and delivery (2-D radiotherapy) to a more sophisticated approach with 3-dimensional conformal radiotherapy (3-D CRT) and intensity modulated radiation therapy (IMRT),... In Vietnam, one of the most common types of radiation therapy is 3-dimensional conformal radiation therapy (3D-CRT) which can be considered as a standard.