The fact that radiation is more readily absorbed by actively growing cells is very useful in the treatment of cancers. Radiation treatment uses high power radiation which is applied to the organ that has cancer. An important characteristic of cancerous cells is that they develop and reproduce at a faster rate than normal cells.
When radiation is used, it damages the DNA of cells which form the affected organ; the cancerous cells are damaged more due to their fast rate of growth. Normal cells which reproduce at a slower rate are not affected as much as the diseased cells and recover within a short period of the radiation treatment.
But the absorption of radiation by actively growing cells makes it very injurious to newly born babies and those in the mother's womb. This is a reason why pregnant women are not advised to undergo radiation therapy.