Principles and Practice of Radiation Therapy: Chapter 8
pressing beam off key, opening door to treatment unit, using emergency off switch
Radiation therapy can be discontinued in case of emergency by ___, ___, ___
beam on, audio and visual, radiation on (Treatment delivery)
___ with either a key, switch, or both; ___ and ___ contact must both be operating; ___ lights over door and in room
Palable
able to be touched or felt
Collimation
arrangement of shielding material that creates the beam shape
Bolus
beam modifier that mimics or compensates for tissue; minimizes skin sparing (brings dose closer to skin)
The rationale for radiation treatment
captures relevant patient medical history which might impact their tolerance of planned treatment
Conformal arcs
changing jaws in the dimension of the moving gantry conforming to the outermost edges of the target volume
Electronic medical records (EMR)
charting, text, and image information is stored in a central database
Four field technique
commonly used in the treatment of deep-seated tumors of the pelvis -beams are placed 90 degrees from one another
Quality assurance
consists of activities and documentation performed with the goal of optimizing patient care -the radiation therapist's primary role is to ensure accuract in the delivery of the radiation treatment plan as prescribed by the oncologist
Electronic imaging
converting paper documents to pictures stored and displayed via computer. (CT scans, EPIDs)
Cerrobend cutout
cutout which fits inside the base of the cone during electron beam therapy
Beam modifiers
devices that change the shape of the treatment field or distribution of radiation
15 centimeters
distance all beam modifiers must be from skin surface to prevent electron contamination
Source-skin distance (SSD)
distance between a radiation source and a patients skin
Treatment record
documents the delivery of treatment; includes fractional and cumulative doses as well as machine settings
Treatment plan
done by dosimetrist and approved by physician -calculations must be done by at least 2 people
reference (fiducial) markers
fixed points which other objects can be measured -Anatomic = bones -premanent = tattoos
Tangenital field
flashing off a curved surface such as a breast
length times width in centimeters
how the treatment field, or portal, dimensions are measured
Localization
identification of hidden anatomy relative to a patient's landmarks
Treatment history
identifies the date(s) of treatment, number of treatments delivered, and elapsed days
Orthogonal
imaging planes perpendicular with one another, with a 90 degree angle between them
patient identification
includes images, wrist bands, name, date of birth, and area of treatment (must use at least two)
Fractionation
individual treatment dose
Standard collimation
limits beam shape to square or rectangle
Compensators
made to make up for an irregular surface while maintaining skin sparing (absorbs part of the beam)
Radiation prescription
may only be delivered under the direct order of a radiation oncologist; includes fractionation, protraction, treatment technique, and beam modifiers
Hinge angle
measure of the angle between central rays of two intersecting treatment beams
Machine parameters monitered
meterset, gantry position, collimator and aperature settings, table position, and beam modifiers
Feathering
migration of a junction through the treatment course -may be used to blur dose in homogeneities at a junction
Multileaf collimators
modifies the shape of the linac beam from its usual square or rectangle shape
Documentation of treatment response
patient response to treatment is monitored and recorderd throughout and following completion of treatment
X plane
plane that identifies left and right
Y plane
plane that identifies superior and inferior
Z plane
plane that identifies up and down (depth)
Couch rotation
positions the beam in directions that aquisition devices cannot be positioned
Total body irradiation
prepares the body for bone marrow transplant
Interlocks
prevent beam initiation; include alerts prompting completion of treatment setup and safety procedures
Double-exposure images
produces greater visualization of the treatment field and surrounding anatomy, thus increasing the landmarks available for interpretation but also increasing dose delivered to normal tissue
Laser systems
project points or lines of light from three or four sources along vertical and horizontal planes, intersecting at the treatment machine's isocenter -green works better because it has a shorter wavelength resulting in less scattering at the skin
Arc therapy
radiation is delivered while the gantry moves through its arc of rotation, thus effectively delivering radiation through a continuous sequence of individual overlapping treatment portals
Optical-distance indicator (ODI)
range finder; consists of a light that is projected onto the patient's skin and matched at the intersecting crosshairs that coincide with the central ray of the beam
RT chart
record of the patient's radiation treatment; separate from an individual's hospital chart
Slide board
relatively thin sheets of plastic used to pull the patient from the stretcher to the treatment table rather than be lifted
Beam's eye view (BEV)
shows the area to be irradiated by the linac as well as treatment field shape and orientation as it passes through the patient
Intensity modulated radiation therapy (IMRT)
similar to 3D conformal therapy, but the dose of radiation at each field can also be varied
Components of an RT chart
test results, consent form, vitals, photo of patient, prescription, etc.
Multiple fields technique
the machine may be moved to direct radiation beams at the target from many directions without repositioning the patient, preserving accuracy -areas of field overlap receive increased radiation
Isocenter
the point of intersection of three axes of machine rotation (gantry, collimator, and base of couch)
Couch
the treatment table
Heel
thick end of the wedge
Toe
thin end of the wedge
Protraction
time period during which the treatment will be given
Elapsed days
total time which treatment is protracted
Portal
treatment field; volume of tissue exposed to radiation from a single radiation beam
Parallel opposed portal (POP)
two fields that are 180 degrees apart
Stereoscopic
two images from different angles, focused on the same point
Electron beams
used for superficial treatments such as skin or lymph nodes -uses cones that come close to skin surface
Wedges
used in areas of overlap to get rid of hotspots; evens out the dose distribution -measured in 15, 30, 45, and 60 degrees
Reference images
used to compare on-treatment images, verifying treatment position, and documenting treatment delivery
Draw sheet
used to lift a patient from the stretcher to the treatment table if they are unable to roll over onto a slide board
Immobilization devices
used to restrict movement and reproduce the patient's planned treatment positions; includes sponges, molds, casts, masks, and/or bite blocks
Single-exposure images
used when sufficient landmarks for verification are located within the treatment area
3D conformal therapy
uses multiple fields and shapes
External beam radiation therapy
uses radiation-producing equipment such as a linear accelerator
Triangulation
using 3 coordinates (X,Y,Z) on the patients surface to find the isocenter
Verification and record (V&R) systems
validated parameters from the treatment plan to the treatment machine setup and delivery
Modulation
variation of radiation intensity accross the exposed field
verification imaging
verifies that what was planned during simulation is what is being treated; done with ultrasound, film, electronic portal imaging, or CBCT