Laura Chapter 3 Part 2: Dosimetry

3-D Conformal

_______ Radiation Therapy Conforms the radiation beam so that the target volume receives the prescribed dose and the surrounding healthy tissue receives a much lower dose

computed tomograpy

Planning uses 3D imaging such as ______

Electron beam

________ is a monoenergetic beam that is used to treat superficial tumors

air

Electron beams Scatter easily in

patient's skin surface

Electron beams requires a cone to confine the beam closer to the

scatter

Electron beam field edges balloon out because of _____and aren't definitive like photon beams

deeper organs and tissues will receive very little or no dose

For electron beams, there is a "rapid falloff" of dose, which means that

Less skin sparing

For electron beams there is _____________, which means more dose to the skin compared to photons

IMRT

_____ is a radiation beam that has varying intensities throughout the beam

1 cm x 1 cm

IMRT has Many smaller beams or "beamlets". Beamlets are commonly as small as

False

T/F for IMRT the dose is uniform

surrounding healthy tissues

IMRT allows for higher doses to tumors while minimizing doses to

inverse

IMRT uses _____ treatment planning and dynamic MLCs

SRS

______ treats small tumors within the cranium at a high dose

One

SRS treats tumors with how many fractions?

3cm

SRS tumors are normally less than ____Cm

1mm

Treatment positioning must be +/- ___mm

a frame attached to the patients head

SRS of intracranial lesions may require

AVMS, trigeminal neuralgia, acoustic neuromas, meningiomas, pituitary adenomas, metastatic and primary brain tumors, less common in spine

What are the common disease treated with SRS that are in the cranium?

Gamma Knife and Cyber Knife

What are some examples of machines that preform SRS treatment?

SBRT

______ treats small tumors outside of the cranium with a very high dose for about 3-5 fx

TBI

_____ is a type of radiation therapy that targets the whole body to prepare for bone marrow transplants and to treat other malignancies

Image Guided Radiation Therapy (IGRT)

_____ is used prior to treatment to confirm patient position

EPID, KV, MV cone beam, Ultrasound

What are examples of IGRT

Particle beam radiotherapy

_____ = high energy charged particles such as protons, alpha particles, and carbon ions

Bragg peak

______ is the dose curve of a proton beam. It starts off low at the beginning but then rapidly rises toward the end of the path. Then abruptly falls to zero.

Patient positioning aids

___________ Helps to position the patient for treatment

limit the patient's movement

Positioning aids do NOT....

head holders, sponge pillows, foam cushions, neck rolls

What are positioning devices than can be used for multiple patients

Complex

________________ immobilization devices- Limit the patients movement and create a very reproducible setup

alpha cradle, vac-lok, thermoplastic molds, bite blocks

Complex immobilization devices are Customized for each patient. What are some examples?

Simple

_______immobilization devices Help to constrain patient

tape, rubber band, arm-to-foot straps

Simple immobilization devices are Used with positioning aids. They are Not as restricting as complex immobilization devices. What are some examples?

simulation

When is contrast used?

It will highlight specific organs

What does contrast do to help create the treatment plan?

Area to be treated and critical structures to be avoided

What can contrast highlight?

positive

______ contrast agents appear radiopaque (white) on radiographic imaging due to high atomic numbers

iodine, gadolinium, and barium

What are examples of positive contrast agents?

negative

______ contrast agents appear radiolucent (black) on radiographic imaging due to low atomic numbers

air, oxygen, carbon dioxide, and nitrous oxide

What are some examples of negative contrast agents?

computed tomography (CT)

_____ is the most common imaging modality used for RT treatment planning

3D

CT simulators create ____ images

X-ray, detectors, and computer

CT images are produced by

Spiral or helical scanning

CT images are acquired through

slice thickness

_____ is the thickness of the section in the patient that contributes to echo signals on any one image

CT gantry

Slice thickness is Controlled by pre-patient collimation within the

more

Thinner image slices are a result from _________ collimation that narrows the x-ray beam

thinner

___________ slices reduce scatter and create better image quality

2-3 mm

Typical CT simulation slice thickness is ___ to ___ mm

1 to 6 cGy

One CT slice delivers __to___ cgy at the skin's surface

5 mm

Spacing between CT slices should be less than ____

more

__________ space between the slices leads to less information obtained by the scan and more interpolation performed by the computer algorithms

slice thickness and space between slices

What are two key factors for generating high-quality DRRs?

mA

_____ Measures the beam quantity, or how many x-rays are produced

patient dose

mA Increase leads to higher

high-quality image

mA is a Technical factor used to create a

512 X 512

CT image displays use a matrix size of _______ x _______

attenuation rate or Hounsfield units

CT images are a display of many small pixels with different shades of gray, depending on the

window width (WW)

the number of shades of gray displayed on an image or the contrast of the image.

narrow

A _____ window width has more contrast

Window Level (WL)

the median shade of gray or hounsfield unit within the window width

brightness

Window level changes the image

darker image

An increase in window level creates a

brighter image

A decrease in window level creates a

CT number

_____ is a value that represents a shade of gray

Hounsfield Unit (HU)

CT number is also known as the

density

CT number represents the _____ of different tissues

how the structure attenuates the x-ray beam

For CT number the shade of gray is determined by

-1000

What is CT number for air

0

What is CT number for water

1000

What is CT number for bone

Reconstruction

____ is where the computer uses algorithms to create the CT image in different planes

the axial plane

Where are reconstructed CT Images first acquired?

coronal and sagittal

CT Images are reconstructed to be viewed in the _______ planes

CT simulation

During a _______, raw data is acquired during a scan and it is then reconstructed into image data to be viewed

image data

The computer assigns each pixel an HU to become _______ in reconstruction of image

display field of view (DFOV)

The amount of raw data used to create or display an image

Scan field of view (SFOV)

Area of interest to be scanned

contour

_______ is a 3-D image taken in the treatment position that provides data of the anatomy of the patient, such as the skin, tumor and other organs within the body

calculating doses

Contours are necessary for creating accurate treatment plans and

Virtual simulator

In the _______ ( treatment planning system) the physician can identify the treatment borders and the isocenter location

Digital imaging and communication in medicine

What does DICOM stand for

Transfer of images and patient reports to planning computers

DICOM is used to

PACS

Used to store and share images

External

____ lasers are at a fixed distance from the internal scanner lasers usually 500mm (50cm)

Wall

___ lasers are mounted to the side of wall and project vertical and horizontal directions

Sagittal

_____ laser is a single laser located on the ceiling and is moveable. It moves in the left/ right position. Important since CT table cant move Lt/Rt.

Scanner

___ lasers are internally mounted within the gantry bore

Radiation oncologist

Who created Sim order

Patient position, body part to be simmed, laterality of body part, contrast instructions, and immobilization technique

What should be included in Sim order?