TRANSMISSION & LEAKAGE MEASUREMENT OF NOVEL TELECOBALT MACHINE BHABHATRON-II

The Telecobalt machines are extensively used in developing countries due to its lesser cost, lesser power consumption and easy maintenance. The high activity source can be extensively used for at least 6-8 years due to its long half-life. Installing a Telecobalt unit comprises of fixing the machine in the treatment room, ensuring its mechanical motions, source loading and all other related Quality Assurance Checks. The Bhabhatron-II, an indigenous Telecobalt machine is installed at Acharya Tulsi Regional Cancer Centre, produced in India by Department of Atomic Energy, Mumbai. This paper describes about the installation & Commissioning of Bhabhatron-II and their related Quality Checks. The necessary Radiation Quality Assurance checks such as Combined Jaw Transmission, Individual Jaw Transmission, and ON Position Leakage in patient plane, Leakage in other than patient plane are measured. The collimator transmission of combined jaw and, Individual jaws (X & Y) are measured and they are 0.024%, 0.347% & 0.635% of the useful beam respectively. The ON position leakage in patient plane is measured by forming an imaginary circle of 2m radius @ SAD; the leakage level is 0.005% which is 5.42% of the recommended limit by I.E.C. The ON Position leakage level in other than patient plane is measured by a special apparatus which partially simulates a sphere of 1m radius. The leakage level is 0.347% of the Dose Rate measured at 1m.  The Dosimetric instruments which are available in routine radiotherapy department are used. The TLD Disks are used to measure the ON Position Leakage in other than Patient plane. The measured readings are well under the Tolerance recommended by A.E.R.B India. The machine has been approved by the regulatory board and dedicated for Treatment purpose.