linear accelerator
- 1. Saad Rashid Usmani Nuclear medicine and radiotherapy
- 2. Radiation Therapy The use of high-energy rays to damage cancer cells, stopping them from growing and dividing.
- 3. Grenz: 10-15 kVp Contact: 50 kVp Superficial: 50-150 kVp Orthovoltage: 150-500 kVp Super Voltage: 500 to 1,000 kV Mega voltage: more than 1 Mev 3 Radiation Therapy
- 6. The overall diameter of a 60Co source is 1 to 3 centimeters. Radioactive 60Co enclosed in multiple layers of welded metal to prevent contamination of the environment and to absorb β- particles produced by the decay process. 6 60Co Source
- 8. Smaller source with less penumbra for the same beam intensity Less hazard of contamination should a source ever become exposed to the environment. Advantages:
- 9. Cobalt 60 sources have an activity of 750-9000 Ci. Typically 3000-9000 Ci used in radiation therapy. 9 60Co Activity
- 10. Half-life: the time necessary for a radioactive material to decay to half or 50% of its original intensity. 10 Half-life
- 11. The half-life of 60Co is 5.26 years
- 12. 12 Cobalt-60 Production Cobalt-60, or Co-60, is an unstable isotope of cobalt. It is radioactive. Co-60 is made by a process called neutron activation. In activation, a cobalt (cobalt-59) put into an operating nuclear reactor and exposed to the neutron flux. The cobalt-59 will absorb a neutron and become cobalt-60, and the sample (now called a source) is then withdrawn from the reactor and put into a heavily shielded casket for storage.
- 13. Neutron activation of Cobalt 59
- 22. Cobalt machine consists of following major system Cobalt source head Treatment table Collimator
- 25. This is the main part of the system because it contain the source 20cm to 25cm is the thickness of head of most cobalt units. Uses a counterweight to balance the lead shielding in the head of the machine housing, (similar to the beam stopper on linac): absorbs a significant amount of radiation transmitted through patient.
- 26. 60Co Shielding It consists of a steel shell filled with lead for shielding purposes and a device for bringing the source in front of an opening in the head from which the useful beam emerges. Also, a heavy metal alloy sleeve is provided to form an additional primary shield when the source is in the off position.
- 27. Cerrobend (Lipowitz metal): 50% Bismuth 26.7% Lead 13.3% tin 10% Cadmium (a toxic metal can get into bloodstream) A thickness of 7.2 cm of Cerrobend needed, 6 cm lead. 27 60Co Shielding
- 28. Dose maximum (Dmax): when a greater percentage of dose occurs below the skin surface Dmax is the depth of maximum buildup, in which 100% of the dose is deposited. For 60Co, Dmax occurs at 0.5 cm below the skin surface. 28 Dose Maximum
- 29. On and off position of source
- 31. Collimator
- 32. Types of collimator present that can make beam with rectangular cross section area
- 34. Treatment table
- 35. The patient lies on couch which can be moves upwards downwards and side ways also so that tumor is positioned and the beam will pass through the tumor
- 37. The 60Co unit is commonly used today to treat cancers of the head and neck area, breast, spine, and extremities. Areas just below the skin surface. Ideal in treating lymph nodes. A 60Co beam can provide an adequate distribution of dose by using parallel opposed fields. 37 Application
- 38. Disadvantages as compare to linear accelerator Required to stored high activity source, and on going cost of source replacement The source diameter is 2 cm as compare to linear accelerator target is is big so have got big penumbra Low dose rate as compare to linear accelerator Limited photon energy as compare to linear accelerator
- 39. Any Question
- 40. Thank you