[Effectiveness of the field-within-a-field technic in radiation treatment]

Field within a field technique in radiation therapy is one of the methods in order to improve the dosimetric factor, which makes inner small field in the outer large field. This method makes it possible to increase the dosage of radiation to the inner small field without increasing the overall time, because both of the fields are irradiated simultaneously. In other words, it is intended to relieve symptoms rapidly and improve the local control rate. As it is usefull and safety, it should be considered in radiotherapy of cancer.