Other Radiation Therapy Equipment – Flashcards
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What machines are categorized as kilovoltage equipment?
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grenz rays, contact, superficial and orthovoltage
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Why is kilovoltage equipment, for the most part, extinct? What year?
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1950 Co-60 replaced them followed by LINAC
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What replaced Co-60 tx units?
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LINAC
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If and when kilovoltage equipment is used, what is it used for?
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superficial lesions
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What are some disadvantages when using kilovoltage equipment?
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-poor penetration (esp. for deep seated tumors) -little skin sparing -small field size due to proximity of skin to source (recall beam diverges and is proportional to SSD) -non-isocentric (low penetrability)
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What determines beam quality for kilovoltage equipment?
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kVp and HVL
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How do you describe the penetrability of the beam?
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kVp
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What specifically does HVL describe?
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best method of specifying x-ray quality in kilovoltage equipment
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In x-ray equipment (kilovoltage equipment) when there is a higher HVL, there is what?
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more penetrability
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How is energy and amount of attenuation expressed when using kilovoltage equipment?
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# of HVLs and attenuation material used
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Define isodose curve.
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lines representing various points of similar value in a beam along the central axis and elsewhere
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What do isodose curves depict? How is this depiction represented in various curves of different energy equipment?
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-beam quality (kVp-penetrability) -by how much the curve dips
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More ____ to the isodose curve equals ____ penetrability and higher ______ ______.
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sag; higher; beam energy
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For kilovoltage equipment, what attenuation material is used when filtering the beam?
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thin sheets Cu or Al
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Where is the filter placed in reference to the tx head in kilovoltage equipment?
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tube and collimator
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What is the function of filtration in kilovoltage equipment? What does this mean?
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-hardens the beam -creates a more useful beam by getting rid of lower energy photons that are not therapeutically useful
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What if the wrong filter or no filter at all is used when planned for in a tx setup?
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a huge under or overdose can occur
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What is filtration material used for in megavoltage machines?
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gives the photon beam a more uniform "flatter" distribution
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What type of filter is used in megavoltage machines
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thick transmission filter/target
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What is the energy range of Grenz Ray units?
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5-15 kVp
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To what depth in the patient is the beam absorbed?
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almost all absorbed in 2mm of skin
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This unit has a useful depth dose of .5 mm
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Grenz rays
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What is the HVL material in Grenz ray machines?
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HVL in mm of Al
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What are Grenz ray units used to treat?
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inflammatory disorders, patchy mycosis fungoides, herpes simplex
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What was the historical tx unit used to treat superficial lesions?
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contact therapy
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What therapy unit was historically used to treat superficial lesions but can also treat endocavitary rectal tumors?
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contact therapy
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What is the SSD for contact therapy machines?
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4 cm
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How many mm of filtration is needed for contact therapy machines? What material is used?
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.5-1.0 mm of Al
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What is the energy range of a superficial therapy machine?
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40/50-150 kVp
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How many mm of filtration is needed for superficial therapy machines? What material is used?
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1-6 mm of Al
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What type of block is used and where is it in relation to the patient when treating with a superficial therapy unit?
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lead block cutout placed on pt
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What is the SSD set at when using a superficial machine?
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15-20 cm
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What is a superficial therapy unit good for when treating cancer pts?
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skin cancer no deeper than .5 cm
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In what tx machine does the therapist set kVp, tx time, and mAs?
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superficial therapy unit
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What is the energy range of an orthovoltage tx unit?
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50-150 kVp
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What is the SSD of the orthovoltage tx unit?
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50 cm
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What type and how many mm of material are used in the filter when treating with an orthovoltage machine?
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1-4 mm of Cu filters
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What does the orthovoltage machine use to focus the beam?
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different sized cones
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What types of cancers are orthovoltage machines good for? How long are txs?
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-skin, mouth, and cervical cancers -usu. several mins long
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What kilovoltage tx machine can still be found in clinics/hospitals? What is it used for? What tx therapy does it replace?
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orthovoltage machines used as an alternative to e- therapy for skin cancers
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According to ppts, what clinic still owns and operates an orthovoltage tx unit?
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Sammons in Dallas
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What was the first ______ linear accelerator?
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electrostatic; van de graaf generator
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What were the dimensions of the Van de Graaf generator?
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Steel dome about 3 feet in diameter and 5.5 ft high
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Could the Van de Graaf tx isocentrically?
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no
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What was the energy range of the Van de Graaf?
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only produce energy up to 2 MV
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What was the of the Van de Graaf SSD? What did this allow?
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100 cm larger field sizes
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What were the disadvantages of the Van de Graaf?
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1 hour warm up no ODI size of unit major disadvantage (huge)
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What type of unit is the cyclotron?
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megavoltage unit
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What are the three uses of the cyclotron?
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1) production of radionuclides 2) creates neutron beam (only 3 in USA) 3) creates proton beam
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Is used for the production of radionuclides in nuclear imaging?
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cyclotron
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What is used for nuclear medicine, esp. PET scans?
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radionuclides
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What are the radionuclides used for a PET scan?
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Carbon-11, nitrogen-13, oxygen-15
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What has to be considered when using the common radionuclides, C-15, N-13, and O-15? How is this taken into consideration when they're used?
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extremely short 1/5 life made on demand then injected into pt
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How is the image in a PET scan produced?
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by radiation emitted by the pt
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In a PET scan what is it showing?
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function rather than structure
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What can measure blood flow, oxygen levels or metabolism after injection of a radionuclide?
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PET scan
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What does PET stand for?
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positron emission tomotherapy
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How does the cyclotron work?
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Uses large metal 1/2 discs/magnet (dees) to confine charged particles in a circular path
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In the cyclotron, what is used to confine particles in a circular path?
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dees
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What is the metal 1/2 discs/magnet called in a cyclotron?
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dees
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What separates the dees of opposite polarity?
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AC (alternating current)
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What is part of the cyclotron that has to do with circular or circular orbit?
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cyclotrons dees
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How are particles kept on their circular path in a cyclotron? What does this?
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dees pull particles back and forth
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By what means are the particles sped up in the cyclotron?
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ea. time a particle crosses a gap along its path, AC speeds it up
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What known therapy uses a cyclotron?
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proton therapy
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In proton therapy what atom is used? How does this work?
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H+ (1 p+ and 1 e-); put in cyclotron and the e- is stripped off the atom, leaving just the proton
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What is proton therapy used for?
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benign pituitary tumors, AVM (arteriovenous malformation), ocular melanoma, bone sarcomas, prostate, head and neck
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What makes proton therapy the treatment of choice for lesions, deep, small and close to critical structures ?
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Bragg peak
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What is the treatment of choice for lesions close to sensitive areas in the body?
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proton therapy
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An advantage of this kind of therapy is the Bragg peak.
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proton therapy
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What is meant by the Bragg peak effect?
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means that most of the energy is deposited at a specific depth, then quickly drops off to zero
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What is the good things about Bragg peak coverage?
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tissue before ; after this max energy is deposited is spared (very small doses)
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What is the disadvantage of Bragg peak coverage?
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coverage of max dose is very small, so can only cover tiny tumors
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This can accelerate protons and neutrons for therapy?
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cyclotron
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Two ____ of opposite polarity are separated by AC voltage in what machine?
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dees; cyclotron
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Charged particle accelerator?
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cyclotron
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What is based on the principle that an electron in a changing magnetic field experiences acceleration in a circular orbit?
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betatron
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What is used for industrial radiography?
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betatron
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What special procedure produces images that are axial and sagittal?
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ultrasound
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What special procedure can be registered with tx image?
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ultrasound
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What are all the special procedures done in RTH?
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ultrasound guided RT on board imaging (varian) ExacTrac from BrainLab VisionRT CT-on Rails CBCT
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What special procedure uses infrared lighting?
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VisionRT
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What special procedure has a floor recessed x-ray and detectors on the ceiling?
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ExacTrac from BrainLAB
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What is another name for on board imaging?
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kV-kV imaging
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Why are MV images not as useful?
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b/c getting a lot of Compton scatter and not enough photoelectric effect
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What does SRT stand for?
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stereotactic radiation therapy
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When SRT is used in radiosurgery, what is it called?
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stereotaxis
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What does SRS stand for?
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stereotactic radiosurgery
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When is SRS used?
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single fraction for brain mets
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What is SBRT used for?
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stereotactic body radiation therapy
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How many tx does a pt receive when getting SBRT?
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5 fx
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What are the margins of special SRT, SRS, SBRT?
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=/- 2mm
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What is used in HDR txs to spare dose to personnel?
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remote afterloading
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How does afterloading work?
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sources are delivered through catheters from machine source to patient
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What do the catheters in afterloading allow?
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positioning of catheters perfectly where you want sources to be administered during tx
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With afterloading what reduces dose to area when sources are fed through?
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shielding
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What are the common radionuclides used in remote afterloading brachytherapy?
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Cs-137, Ir-192, and I-125
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What does LDR stand for? What is the radiation absorbed dose value here?
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low dose rate = 40-200 cGy/hr
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What does MDR stand for? What is the radiation absorbed dose value here?
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medium dose rate = 200 cGy/hr-1200 cGy/hr
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What does HDR stand for? What is the radiation absorbed dose value here?
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high dose rate = more than 1200 cGy/hr
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What does PDR stand for? What is it?
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pulsed dose rate = delivery of short bursts of HDR (about 1 per hour) in order to achieve biologic effectiveness of LDR...advantage is HDR safety
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What is the advantage of PDR?
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delivers like HDR but effects lesion like LDR while maintaining HDR safety
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Advantage of HDR to LDR?
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outpatient procedure LDR your inpatient (days) with temporary implants that are removed LDR if implant is permanent need to be in impatient until source decays that is safe for public HDR offers shorter tx times In HDR afterloader offers complete radiation protection In LDR pt admitted staff caring for pt are somewhat exposed In LDR pt is not given general anesthesia rather local anesthesia
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What tx offers low dose and high dose options?
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remote afterloading brachytherapy
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What therapy must be accurate within 1 mm?
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proton therapy
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Uses brass cutouts, Lucite compensators and a great deal of preparation.
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proton therapy
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Some disadvantages of this type of therapy are the poor depth doses, poor skin sparing, inadequate collimation and frequent breakdowns.
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neutron therapy
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What therapy uses teflon flattening filters, beryllium target, polyethylene filters?
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neutron therapy
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What therapy had bad late complications due to lack of information about its RBE?
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neutron therapy
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This kind of therapy is often given in one large single dose?
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remote afterloading brachytherapy
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Produce reactions by a process called stripping.
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neutron therapy
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What is the name for the product of the glass envelope and insulating oil of x-ray tube?
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inherent filtration
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What is considered the best method to specify x-ray quality for kvp equipment?
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HVL
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What is it called when a thin sheet of absorber placed between tube housing and collimator?
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added filtration
