Radiation involves the exposure of a selected area of the body to a source of ionising radiation or X-rays under carefully controlled conditions. Treatment planning involves accurate localization of the cancer and calculation of the total radiation dose to be given and dividing the same into daily fractions over a period of some days or weeks so that there is optimum response and minimum side-effects.
The calculation is done by the radiation therapist by taking care of all the facts of the case, including how sensitive to radiation are the cancer cells of a particular patient as diagnosed by a pathologist from a biopsy specimen. The measurement of the radiation given is counted in units called rads (radiation absorbed dose), i.e. the radiation absorbed by the tissues.
Small fractions of radiation given in divided doses over a period of many days or weeks, do less harm to the normal cells. Radiation damages cells by interaction with DNA present in the nucleus of the cells thus preventing the normal reproduction of that cell. Fast-dividing cancer cells are more susceptible to being killed than the normal cells. The normal cells are also damaged in the process to some extent.
Side-effects of Radiation Treatment
A feeling of fatigue and diminished appetite are the commonest side effects, though not observed in all the patients. Redness of the skin exposed to X-rays is not uncommon. When radiation is given over the abdomen, the patient may develop some amount of diarrhoea.
Radiation in the region of head and neck, may cause difficulty in swallowing.
Radiation effects on the bone marrow may occur if larger areas are treated. Minor decreases in lymphocyte count are common, but a frequent check on the peripheral blood is made throughout the treatment to adjust this if significant marrow suppression occurs.
Maintenance of adequate haemoglobin is important to the outcome of therapy since less oxygen in the blood (hypoxia) may render the cancer mass less sensitive to radiation damage.