AbstractID: 7834 Title: Manual Multi-leaf Collimator for Co-60 beam shaping- A feasibilty study Conformal radiotherapy is a modern technique in which the each field is shaped to conform regions of high dose to the shape of the tumor volume by using Multi-leaf collimator (MLC). We have fabricated a manual prototype MLC with lead for Th-780c telecobalt unit. The developed MLC consists of 15 pairs of lead leaves with projected leaf width of 8mm at isocenter, producing a maximum field size of 12x12 cm2. The leaf thickness was kept at 8cm (7HVL). Tongue & Groove technique was used in the design of the leaves to reduce the inter-leaf transmission. This is an add on MLC which can be slide on to the wedge slot level of the conventional collimator of Th-780c machine. The Co60 beam characteristics such as depth dose, beam profiles, surface dose, output factors were measured and compared with those of conventional collimator. The “inter-leaf leakage radiation “ has also been measured with film dosimetry at 5cm depth and found to be 6% of the central axis dose. The depth dose values obtained with MLC were found to be identical to conventional collimator. The surface dose was found to be more than that of the conventional collimator while the penumbra was found to be less. The output factors were found to be similar for both conventional and the developed MLC. Hence it has been concluded that the developed MLC can be used for treatment of patients with irregular fields instead of fabricating blocks eliminating labor and cost of customized blocks.