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Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,Beam Therapy Equipment,2 Linear Accelerator Head,Photon/Electron differences,Target,Flattening filter,Any jaw size,MLCs,Shaping blocks,Intensity modulation e.g.wedges,No target,Scattering foils,Jaw size dependent on energy and applicator,e,-,applicator,End-frame,No intensity modulation,Photon Head,Electron Head,Changes to accelerator when using electrons-automatic,Photon target is moved out of the way.,Carousel is moved to position scattering foil for particular electron energy in place of photon flattening filter.,Gun volts on electron gun are reduced to decrease the number of electrons passing through wave guide.,Frequency of rf adjusted to give optimum acceleration of electrons,Bending magnet voltages adjusted to finely tune electron energies leaving bending magnet,Changes to accelerator when using electrons manual,Jaws moved to pre-defined position dependent on applicator size and electron energy.Optimised for flat field(wide scattering),Electron applicator attached to head,Electron insert fitted into end of applicator defines final field size,Scattering foils,Scattering foils chosen for wide scattering angle(flat field),energy loss(none)and bremsstrahlung production(none),Usually made of copper,Not necessarily of uniform thickness,Higher electron energies may use two foils,Electron field shaping,Electrons are scattered by air between scattering foils and patient,therefore final shaping needs to be done as close to patient as possible,Shaping done by:,Secondary collimators coarse,Electron trimmers scrape scattered electrons,Electron insert fine field shape,Applicators,Applicator consists of progressively smaller scrapers,Electrons scattered by foil have a Gaussian distribution,electrons scattered by scrapers are used to flatten the beam,Scrapers should be made of low Z material(Aluminium)to limit X-ray production,Safety Devices,The scattering foil,secondary collimator settings,bending magnet voltages are checked for consistency with energy/applicator selected.,Presence of the applicator and correct insert may be interlocked.(Applicator interlock very common,insert interlock rare),Collision of applicator with patient,bed etc is also checked using sensors built into applicator.,Radiation symmetry,output and energy are monitored by the monitor chamber during treatment,Beam shaping,Beam can be modified in 3D shape and intensity,Collimators,Applicators,MLCs,Cast blocks,Wedges,Penumbra,MLC,Used to shape radiation field,Can interdigitate,Fields set automatically,52 160 leaves,Typically 60mm tall,2.5%leaf transmission;4%interleaf leakage,Tongue and groove offset,Focused in 1 direction,7mm penumbra,Blocks vs.MLCs,BLOCKs,Exact shape,Move small amounts,Easy to check on patient,Heavy,Facing right way,Individual possibility of using wrong block,MLCs,Stepped,Movement need re-plan,Difficult to check on patient,Auto set-up,Individual attached to field,Wedges to shape the radiation beam,Hard Usually lead,manually placed in accessory mount,range of angles available.Increase energy of primary and dose from scattered,Universal Single 60,Wedge in treatment head,mixed with open field to get intermediate angles.,Increase energy of primary and dose from scattered,Dynamic formed by sweeping one of the jaws across the radiation field,range of angles available.Primary same energy,Penumbra,Energy,Radiation,Source size,
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