title: Effect of field irregularities on the dose distribution of 4 MV photon beam.
abstract: Complex irregular fields are often used for the treatment of tumors in radiation therapy. The dose distribution of irregularly shaped fields depend strongly on the shape of field irregularities. The effect of field irregularities on the uniformity of the dose distribution of a 4 MV photon beam has been studied. The uniformity index of the blocked field which is a measure of the dose uniformity of the field has been compared to its corresponding unblocked field. The measured and computer calculated dose are compared for points within 1 and 2 cm from the edge of the field irregularities at the depth of 10 cm. The discrepancies between the computer calculated dose and the measured dose are discussed. Some suggestions are made to improve the dose uniformity of the irregularly shaped blocked fields.
mesh_terms: D011829:Radiation Dosage; D011880:Radiotherapy Planning, Computer-Assisted