Lasers and a mould under the legs are used to determine exact position. Radiation therapy may basic radiation oncology pdf curative in a number of types of cancer if they are localized to one area of the body. Radiation therapy is commonly applied to the cancerous tumor because of its ability to control cell growth. Besides the tumour itself, the radiation fields may also include the draining lymph nodes if they are clinically or radiologically involved with tumor, or if there is thought to be a risk of subclinical malignant spread.
It is necessary to include a margin of normal tissue around the tumor to allow for uncertainties in daily set-up and internal tumor motion. Most common cancer types can be treated with radiation therapy in some way. The use of radiation therapy in non-malignant conditions is limited partly by worries about the risk of radiation-induced cancers. Different cancers respond to radiation therapy in different ways. The response of a cancer to radiation is described by its radiosensitivity.
Highly radiosensitive cancer cells are rapidly killed by modest doses of radiation. Some types of cancer are notably radioresistant, that is, much higher doses are required to produce a radical cure than may be safe in clinical practice. It is important to distinguish the radiosensitivity of a particular tumor, which to some extent is a laboratory measure, from the radiation “curability” of a cancer in actual clinical practice. For example, leukemias are not generally curable with radiation therapy, because they are disseminated through the body.
Lymphoma may be radically curable if it is localised to one area of the body. Similarly, many of the common, moderately radioresponsive tumors are routinely treated with curative doses of radiation therapy if they are at an early stage. Before treatment, a CT scan is often performed to identify the tumor and surrounding normal structures. The patient receives small skin marks to guide the placement of treatment fields. Patient positioning is crucial at this stage as the patient will have to be set-up in the identical position during treatment.
Many patient positioning devices have been developed for this purpose, including masks and cushions which can be molded to the patient. The response of a tumor to radiation therapy is also related to its size. Various strategies are used to overcome this effect. The most common technique is surgical resection prior to radiation therapy.