Source of Support: None, Conflict of Interest: None
As the telecobalt machines are made with different collimator designs, knowledge of the build-up profile and effect of different intervening materials in the beam is necessary. In this study, the build-up dose measurements were performed in different telecobalt machines using a PTW parallel plate chamber. Results from the study showed that the surface dose drastically increases with the presence of lucite tray in the path of the
beam at short SSD. However, the effect is not significant at longer SSDs. Also, any conventional long SSD machine. when used for short SSD treatment will result in clinically adverse skin reactions. The introduction of a 2.8 mm lead plate improves the beam characteristics at short SSD with clearance of 10 cm to surface level. The result has relevance in the design of suggested short SSD telecobalt machine in lndia for the treatment of head and neck cancers.