Determination of absorbed dose for Mantle Field with Extended FSD.

Mantle field is used for supradiaphragmatic disease. Determination of absorbed dose for Mantle Field technique by conventional method and direct dosimetry is studied and compared in this paper. For Mantle field, a field size of about or more than 40 X 40cm is usually needed. To obtain a bigger field size it is mandatory to extend the FSD. A change of FSD results in a significant change in Percentage Depth Dose (PDD) and beam out-put. Mayneord factor is used to determine the PDD for extended FSD. The behavior of the PDD at various FSD is studied by mathematical as well as by direct dosimetry method. The absorbed dose is obtained by performing dosimetry at extended FSD using TRS-398 protocol. From the study it is concluded that direct dosimetry is one of the precise method to determine absorbed dose for Mantle Field at Extended FSD.