Test 2 Flashcards
(233 cards)
Written procedures posted at every machine
Required by some state regulatory agencies
Know where emergency offs and circuits are
Emergency procedures
Where machine is controlled
Monitor and control linac
Audio and visual
Control console
4 states of operational status
Stand-by
Preparatory
Ready
Beam on
Machine in “napping” state
Has time delay before it turns on
Keeps electronics warm
Stand-by
Shows programmable operational status; record and verify
Preparatory
Confirmed program information
Ready
Turn key and hear “chirping” sound
Beam on
Displayed before or during treatment
Designed to protect patient, employees, and equipment
Interlocks
____ Gy (_____ cGy) can be given in 0.3 seconds at 4000 Gy/min if machine set for wrong beam energy
2 Gy (200 cGy)
8 examples of interlocks
Beam energy Beam symmetry, flatness Dose rate, typical dose Mechanical hazards Carousel rotation for different treatment Bending magnet not steering correctly (BMAG) Foil fault Dose/MU 1.2
11 new technologies
Conformal therapy Multileaf collimation (MLC) Dynamic wedge collimator Electronic portal imaging (EPID) On board imagers (OBIs) Stereotactic radiation therapy IMRT Tomotherapy Image guided radiation therapy (IGRT) Electronic arcs Flattening-field free (FFF)
Took place of cerrobend blocks; 52-160 leaves made of tungsten
Usually rounded on edges so they don’t break if they hit leading to penumbra at end/tip of leaf
Multileaf collimation (MLC)
Older; gets more conformal to tumor volume because peripheral dose decreases, tightens everything up to tumor volume
More angles = les dose per field; more beams
Field shape and beam angle change while gantry moves around patient
Allowed by IGRT
“Forward planning” process
Conformal therapy/3D-CRT
Flat panel MV receptor across from gantry that gives image; demonstrate poor image quality/contrast
Electronic portal imaging (EPID)
kV images on lateral sides of machine, correlates with interaction
Can recreate cone beam CT every 1 degree
Flat panel detector
Offers better detailed image
On board imagers (OBIs)
High dose per fraction for hard to reach areas (brain); long prep time, precise
External 3D frame halo: bolts drilled into head and fastened to apparatus that prevents head movement
Planning can take 3-8 hours
Fiducials track movement
Brain tumors, anterior or venous malformations (AVM), etc.
Stereotactic radiation therapy
Beam arrangements are tested by trial and error until satisfactory dose distribution is produced
“Forward planning” process
IMRT develops treatment plans using this treatment planning; radiation oncologist selects dose parameters for normal tissues and the target volume and computer “back calculates” the desired dose distribution and beam arrangements
“Inverse treatment planning”
How much dose is being received within lines
Isodose lines
Beams in different planes
Non-coplanar
Smaller MLC’s used for SBRT/SRS to conform the dose to very small treatment volumes receiving larger or single fraction doses
Micro-/mini-MLCs
Curved to match beam divergence; took place of cerrobend blocks
Dynamic wedge collimator
3 major components of the linac
Drivestand
Gantry
Couch
Collimation: bimodal (open or shut), static
Similar to CT but 6 MV
Very conformal but limited
Tomotherapy