beam4 ch2.pdf

Linear Accelerators (LINACS) ❑ In medium-energy and high-energy linacs an electron beam transport system is used to transport electrons from the accelerating waveguide to: ❑ X-ray target in x-ray beam therapy ❑ Beam exit window in electron beam therapy ❑ Beam transport sys...

Linear Accelerators (LINACS) ❑ In medium-energy and high-energy linacs an electron beam transport system is used to transport electrons from the accelerating waveguide to: ❑ X-ray target in x-ray beam therapy ❑ Beam exit window in electron beam therapy ❑ Beam transport system consists of: ❑ Drift tubes ❑ Bending magnets ❑ Steering coild ❑ Focusing coils ❑ Energy slits M.Sc. Medical Physics Dr. Khalid I Hussein  Linear Accelerators (LINACS) Electron beam transport ❑ Three systems for electron beam bending have been developed: 90o bending 270o bending 112.5o bending M.Sc. Medical Physics Dr. Khalid I Hussein  Linear Accelerators (LINACS) Linac treatment head ❑ Electrons forming the electron pencil beam: ❑ Originate in the electron gun. ❑ Are accelerated in the accelerating waveguide to the desired kinetic energy. ❑ Are brought through the beam transport system into the linac treatment head. ❑ The clinical x-ray beams or clinical electron beams are produced in the linac treatment head. M.Sc. Medical Physics Dr. Khalid I Hussein  Linear Accelerators (LINACS) ❑ Components of a modern linac treatment head: ❑ Several retractable x-ray targets (one for each x-ray beam energy). ❑ Flattening filters (one for each x-ray beam energy). ❑ Scattering foils for production of clinical electron beams. ❑ Primary collimator. ❑ Adjustable secondary collimator with independent jaw motion. ❑ Dual transmission ionization chamber. ❑ Field defining light and range finder. ❑ Retractable wedges. ❑ Multileaf collimator (MLC). M.Sc. Medical Physics Dr. Khalid I Hussein  Linear Accelerators (LINACS) Production of clinical x-ray beams ❑ Clinical x-ray beams are produced with: Appropriate x-ray target. Appropriate flattening filter. ❑ Clinical electron beams are produced by: ❑ Either scattering the pencil electron beam with an appropriate scattering foil. ❑ Or deflecting and scanning the pencil beam magnetically to cover the field size required for electron treatment. ❑ The flattening filters and scattering foils are mounted on a rotating carousel or sliding drawer. M.Sc. Medical Physics Dr. Khalid I Hussein  Linear Accelerators (LINACS) Production of clinical x-ray beams ❑ Electrons: ❑ Originate in the electron gun. ❑ Are accelerated in the accelerating waveguide to the desired kinetic energy. ❑ Are brought through the beam transport system into the linac treatment head. ❑ The clinical x-ray beams and clinical electron beams are produced in the linac treatment head. M.Sc. Medical Physics Dr. Khalid I Hussein  Linear Accelerators (LINACS) Production of clinical x-ray beams ❑ Megavoltage clinical x-ray beams: Are produced in a linac x-ray target Are flattened with a flattening filter. M.Sc. Medical Physics Dr. Khalid I Hussein  Linear Accelerators (LINACS) Beam Flattening Filter (Photon Beam Mode) ❑Required to create a flatten beam with uniformity and symmetry. ❑Material used , Tungsten, steel, lead, and aluminum. ❑Dual energy photon need two flattening filters. M.Sc. Medical Physics Dr. Khalid I Hussein  Linear Accelerators (LINACS) Scattering Foils (Electron Beam Mode) ❑Required to broadened the pencil beam. ❑Different scattering foil for each electron beam energy. ❑ made of aluminum or copper M.Sc. Medical Physics Dr. Khalid I Hussein