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