Indeed, most of the therapeutic effect
(DNA damage in the fast-growing cancer cells) by radiation is resulted from the
DNA damage in cancer cells. Unfortunately, some normal cells can also be
damaged by radiation because they are also fast-growing. These fast growing normal
cells include bone marrow cells, hair follicle cells, intestinal cells, and mucosal cells.
Fortunately, there is a very important cellular function, DNA repair, by which a cell identifies and corrects damage to the DNA molecules. In fact, DNA repair process is constantly active as it responds to the continued damage in the DNA structure.
In addition to radiation-induced DNA
damage to normal cells, there are additional undesirable biological effects on
the body, including immunological responses (such as abnormal levels of some
cytokines including TNF-a, TGF-β,
IL-12, and PGE2). These side effects will be discussed in the later section.
Indeed, the goal of radiotherapy is to
damage as many cancer cells as possible, while limiting the damage to nearby
healthy tissues/organs as much as possible. Nevertheless, it is almost
impossible to have zero damage on normal cells. That is why the treatment plan
is to focus the radiation to tumor cells. Let’s take a closer look at the side
effects induced by radiotherapy in the following chapter.
