X-ray 1 ch2 PDF - Medical Physics

Clinical x-ray beams ❑ In the diagnostic energy range (10 – 150 kVp) most photons are produced at 90o from the direction of electrons striking the target (x-ray tube). ❑ In the megavoltage energy range (1 – 50 MV) most photons are produced in the direction of the electron bea...

Clinical x-ray beams ❑ In the diagnostic energy range (10 – 150 kVp) most photons are produced at 90o from the direction of electrons striking the target (x-ray tube). ❑ In the megavoltage energy range (1 – 50 MV) most photons are produced in the direction of the electron beam striking the target (linac). M.Sc. Medical Physics Dr. Khalid I Hussein  X-ray beam quality specifiers ❑ The term “beam quality” is used to indicate the ability of a beam to penetrate a water phantom. ❑ The x-ray beam’s penetrative ability is a function of the beam’s spectrum. ❑ Various parameters are used as beam quality specifier, however, it is not possible to use a given specifier in the whole energy range of interest in clinical physics (from superficial x rays to high-energy megavoltage x rays). M.Sc. Medical Physics Dr. Khalid I Hussein  X-ray beam quality specifiers ❑ Known x-ray beam quality specifiers or indices: ❑ Complete x-ray spectrum ❑ Half-value layer (HVL) ❑ Effective energy for a heterogeneous x-ray beam Is defined as that energy of a monoenergetic photon beam that yields the same HVL as does the heterogeneous beam. ❑ Nominal accelerating potential (NAP): Is related to the energy of the electrons striking the target. ❑ Tissue-phantom ratio (TPR10,20) ❑ Percentage depth dose (PDD(10)) (SAD=100) M.Sc. Medical Physics Dr. Khalid I Hussein  X-ray machines for radiotherapy ❑Superficial and orthovoltage beams used in radiotherapy are produced by x-ray machines. The main components of a radiotherapy x-ray machine are: ❑ X-ray tube ❑ Ceiling or floor mount for the x- ray tube ❑ Target cooling system ❑ Control console ❑ X-ray power generator M.Sc. Medical Physics Dr. Khalid I Hussein  X-ray machines for radiotherapy ❑Components of a radiotherapy x-ray machine: ❑ X-ray tube ❑ Applicators M.Sc. Medical Physics Dr. Khalid I Hussein  PARTICLE ACCELERATORS ❑ Many types of accelerator have been built for basic research in nuclear physics and high energy physics. ❑ Irrespective of accelerator type, two basic conditions must be met for particle acceleration: ❑ The particle to be accelerated must be charged ❑ Electric field must be provided in the direction of particle acceleration M.Sc. Medical Physics Dr. Khalid I Hussein  PARTICLE ACCELERATORS ❑ As far as the accelerating electric field is concerned there are two main classes of accelerator: electrostatic and cyclic. ❑In electrostatic accelerators the particles are accelerated by applying an electrostatic electric field through a voltage difference, constant in time, whose value fixes the value of the final kinetic energy of the particle. ❑In cyclic accelerators the electric fields used for particle acceleration are variable and associated with a variable magnetic field. M.Sc. Medical Physics Dr. Khalid I Hussein  PARTICLE ACCELERATORS ❑Electrostatic accelerators used in medicine: ❑ Superficial and orthovoltage x-ray machines ❑ Neutron generators for cancer therapy ❑Cyclic accelerators used in medicine ❑ Linear accelerator (linac) ❑ Microtron ❑ Betatron ❑ Cyclotron ❑ Synchrotron M.Sc. Medical Physics Dr. Khalid I Hussein