Conventional approach to treat cancer is to cut it (surgery), burn it (radiotherapy) and poison it (chemotherapy). When a cancer is localised, it can be removed by surgery. But in most of the cases, it is practically impossible to detect cancer in such an early stage. The cancerous cells do get killed by chemotherapy and radiotherapy, but both of these therapies also destroy some vital cells in the body, leading to serious side effects. It is extremely difficult for the scientists to prepare a drug that could kill the cancerous cells selectively without harming normal cells of the body. Another major drawback of chemotherapy is the drug resistance. Moreover, recurrences are commonly seen after chemotherapy and radiotherapy. Other conventional techniques used in the treatment of cancer including bone marrow transplantation, peripheral stem cell transplantation, hormone therapy, photodynamic therapy, immunotherapy and gene therapy have their own limitations.
Radiotherapy
In radiotherapy, therapeutic doses of radiation (which are many times higher than the diagnostic doses) are used to kill the cancerous cells. A single large dose of radiation may kill the cancerous cells, but it will also burn the adjoining healthy tissues. Therefore, the required doses of radiation are usually fractionated into smaller doses, however damage to the healthy tissue still occurs. Radiotherapy has proved more effective in the treatment of tumours of the food pipe, testes and the brain.
The history of radiotherapy goes back to 1895, when Wilhelm Conrad Roentgen discovered X-rays for diagnostic purposes. Two years later, in 1897, it was disclosed in a meeting of the Vienna Medical Society that a mole has disappeared after repeated exposures to the X-rays. Since then, X-rays have been used to treat various tumours. Later, during 1950s, an artificial radioactive isotope of cobalt was developed that delivered radiation deeper into the body as compared to the X-rays. These were named gamma rays, which were similar to X-rays except that these have a shorter wavelength. The X-rays and gamma rays are almost outdated now and their place has been taken up by the high-energy electron beam generated by linear accelerators. In the past, the doses of radiation were used to be measured in rad (radiation absorbed dose), but this unit has recently been replaced by gray (1 Gy = 100 rad). Radiotherapy can be given internally or externally.
In internal radiotherapy, the radioactive implant (a sealed container of radioactive substance) is placed directly into the tumour or in one of the body cavities. The radioactive implant is usually kept in the body for 1 to 7 days but sometimes it is implanted permanently. In the after loading technique of internal radiotherapy, an empty container is first placed in the body and then the radioactive substance is inserted into it. In some patients, the radioactive substance (in the liquid form) is administered orally or by injection. There are three different techniques of giving internal radiotherapy. These are intracavitary radiotherapy, interstitial radiotherapy and brachytherapy.
In external radiotherapy, the X-rays and the gamma rays have been used extensively to treat cancer. The X-rays generate extranuclear radiation, whereas the gamma rays generate intranuclear radiation but both of these are ionising radiations, which form highly reactive ions in the exposed cells. The use of X-rays and gamma rays in radiotherapy is now replaced by the high-energy electron beam (generated by linear accelerators) that can be focused on a smaller area, thus minimising the damage to the adjoining tissues.
In the hyper fractionated technique of external radiotherapy, smaller doses of radiation are given throughout the day instead of a single large dose.
In the super fractionated technique of external radiotherapy, smaller doses of radiation are given many times in a day, but the total combined dose of radiotherapy is greater than that of the single daily dose.
The effect of radiotherapy can be enhanced by using the hyperbaric oxygen and the hyperthermia techniques.
Radioimmunotherapy is a new technique of radiotherapy that delivers radiation directly to the cancerous cells. In this technique, first of all, the specific antibodies produced in the patient’s body against some components of the cancerous cells are collected from the patient’s blood. Later, a radioactive isotope is attached to these antibodies in the laboratory. These antibodies carrying the radioactive isotope are then injected back to the patient, which travel through the bloodstream to reach the cancerous cells and get attached to them. By this technique, the radioactive isotope is directly delivered to the cancerous cells that kill them selectively, thus sparing normal cells of the body from the damaging effect of radiotherapy.
The cancerous cells exist in the body in three different forms, i.e. dividing cells, dying cells and dormant cells. Radiotherapy can kill the dividing cancerous cells. The dormant cells do survive even after exposure to the radiotherapy. These dormant cancerous cells may get back into the cell cycle after some time and multiply to produce many more cancerous cells that may form the cancerous growth again. Such a cancerous growth, which reappears at the same site (or any other site in the body), from where the original cancerous growth apparently disappeared after administration of radiotherapy, is known as recurrence. There are various side effects of radiotherapy such as nausea, vomiting, dryness of mouth, difficulty in swallowing, change or loss of taste, earache, cough, frequency of urination, diarrhoea, change in texture of the skin, loss of hair, sterility and decreased blood cell counts.
