Source of Support: None, Conflict of Interest: None
Many international organizations recommend to carry out dosimetry in water phantom at 5 cm depth to arrive at dose at the depth of maximum buildup using percentage depth dose or tissue air ratio data.
These recommendations minimize error in dosimetry due to contribution of low energy components of photons at maximum electronic equilibrium depth, which mainly depend upon collimator design of telecobalt units. Some centres may not be able to adopt water phantom dosimetry because of non-availability of water phantoms. In this paper a method has been described to determine the absorbed dose in water for various field sizes using a single value arrived from air measurement and an empirical equation. The empirical constants for the equation are generated for three types of telecobalt units. The results obtained from empirical equation and water phantom dosimetry are found to match closely.