Estimation of peripheral dose from Co beam in water phantom measured in Secondary Standard Dosimetry Laboratory, Pakistan

BackgroundPeripheral or scatter dose harms neighbouring normal tissues during administration of dose to cancerous tissues, therefore, knowledge of peripheral dose is an important consideration in radiotherapy.AimIn present study, absorbed dose measurements in a water phantom were performed for three field sizes, 7[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]7[[ce:hsp sp="0.25"/]]cm2, 10[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]10[[ce:hsp sp="0.25"/]]cm2 and 15[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]15[[ce:hsp sp="0.25"/]]cm2.Materials and methodsFor each field size, dose was measured at six depths below the front surface of the water phantom; 2.5–15[[ce:hsp sp="0.25"/]]cm with an interval of 2.5[[ce:hsp sp="0.25"/]]cm. Measurements were made at equal transverse distances along the horizontal axis, from 1[[ce:hsp sp="0.25"/]]cm to 6[[ce:hsp sp="0.25"/]]cm, on both sides of the central beam axis and normalized with central axis dose of each field. All measurements were made at the source to surface distance of 100[[ce:hsp sp="0.25"/]]cm.ResultsVariation of peripheral dose with lateral distance was analysed and an appropriate parametric equation for each field size and depth was constructed.ConclusionsThe peripheral radiation dose showed a strong dependence on field size and distance from field boundary