Dosimetry 2 Section 2 Final

smearing or moving junctions and/or gaps between fields

feathering

simulation with a fluoroscope is an example of a

dynamic study

type of 3-dimensional film commonly used for implants whereby the film and patient remain stationary while the target rotates

stereo shift

methods for taking contours

• solder wire - simplest, easiest, and most commonly used

• Plaster of Paris

• thermoplastic strip or tube (Aquaplast)

• CT - most accurate

• MRI

• ultrasound

most accurate contouring device

CT

primary advantage of treating patients isocentrically

not moving patient between fields

attempt at 3-dimensional filming that ues only one lateral film and relates magnification and divergence on film compared to isocenter

cross table lateral

port film taken before a treatment that aids in localization

scout film

examples of orthogonal field arrangements

• 3 field H&N (abutting supraclav field)

• breast with yoke field

• cranio-spinal axis

radiologic exam that localizes the kidneys

intra-venous pyelogram (IVP)

German helmet field is associated with what treatment area

cranio-spinal axis

most common and most stable immobilization device for H&N

bite block

examples of beam modifiers

• bolus

• wedge

• tissue compensator

examples of beam direction devices

• lasers

• field light/ODI

• mechanical pointers

• gradicule/BB tray

examples of beam shaping/limiting devices

• collimator/MLC

• field blocks

• lead cutouts

• lead strips

term that describes the outline of the patient’s body in the transverse plan

contour

relative temperature of barium mix when introducing into the rectum

warm

contrast agent that may produce an anaphylactic reaction in patients allergic to iodine

conray

gap formula

gap = d/2 * (L1/SSD + L2/SSD)

HVLs required for a custom shielding block to adequately block a proton beam

5

For determining chin extension/tilt in the Y axis on a H&N patient, a measurement should be taken between what two points?

mental point and suprasternal notch

percent of photon beam that can be transmitted through a shielding block

5%

lead strip requirements

• 2mm lead strip for each increasing energy from 6MV

• 6MV = 2mm

• 9MV = 4mm

• 12MV = 6mm

• 16MV = 8mm

• 20MV = 10mm

maximum Z number for a material to be an electron absorber

50

example of a metal that functions as an electron absorber

tin (Sn)

field that commonly deal with abutting borders

• TNI for Hodgkin’s disease

• inverted Y

• hockey stick/dog leg

main advantage of cerrobend over lead for construction shielding blocks

lower melting point

positive vs negative block

• positive - cutting a block into a treatment field

• negative - cutting the field into a blocked area

  • electron blocks

  • PAB

  • H&N

  • mantle field

melting point of cerrobend

158F

minimum distance between patient and any dense accessory/treatment device to prevent electron comtination

15 cm

lead strip thickness for electron energies less than 10 MeV according to Khan

3 mm

purpose of a beam modifier

make isodose curves more uniform below the skin surface

materials used for tissue compensators

• aluminum

• brass

• copper

• lead

• lucite

• cerrobend

areas of tissue interfaces that would produce the best images

• air-bone

• air-tissue

• tissue-bone

• chestwall-lung

areas where ultrasound images improve

• greater impedance mismatch

• greater Z# difference between adjacent tissues

materials used for bolus

• water

• superflab

• superstuff

• rice pellets

• sugar pellets

• spiders mix

• paraffin wax

• wet gauze

• water filled balloons

ingredients in cerrobend (which is harmful?)

• Bismuth - 50%

• Lead - 26.7%

• Tin - 13.3%

• Cadmium - 10%, releases potentially harmful fumes

“key” laser for determining patient movement between pelvic fields

overhead

what does a backpointer demonstrate

exit point of the beam

contrast agent that may give patient a warm metal taste in their mouth when injected

conray

term for setup for patient in three dimensions

XYZ or orthogonal setup

“frog leg” position is used for what area/site?

vulva or perineum

components of image intensifier system

• film holder

• TV camera

• video monitor

basic components of a conventional simulator

• gantry arm

• gantry head

• image intensifier/film holder

ultrasound frequencies for use as localization in radiation therapy range from

1-20 mHz

things that must be known for planning a patient’s treatment

• intent (curative or palliative)

• general condition of the patient

• history and pattern of the disease

• normal surrounding tissue tolerances

When treating an orthogonal set-up, which fields should probably be set up first?

parallel opposed fields

H&N cancer that is often treated with electrons or mixed beam

parotid gland

purpose of placing cork in a H&N patient’s mouth

• protect hard palate (base of tongue treatment)

• protect tongue (oral cavity or floor of mouth treatment)

“chicken wing” position might be used to treat cancer in what body site?

breast

primary purpose of a belly board

decrease side effects by displacing bowels away from the treatment field

number of fields treated with belly board

3, PA and laterals

area of pelvis that is most susceptible to erythema and skin breakdown

perineum

body part most likely to have a irregular surface contour requiring a tissue compensator

lung

device inserted into the mouth that protects the teeth, gums, and maybe even the tongue from electron contamination

intra-oral stent

type of ink typically used for giving RTT tattoos

India ink

reason for wax coating on lead strips

• reduce electron contamination

• reduce lead seepage into skin

whole abdomen on ovarian cancer patient can be treated using

• AP/PA abdominal bath

• moving strip technique

contours with modern equipment

• must be taken with the treatment immobilization devices

• must be taken in the treatment position

• are typically taken in the sim room

• are part of the treatment planning process

position used for Hodgkin’s disease treatment

Akimbo position

How long after surgery before beginning radiation treatments?

3 weeks

dye-like liquid that contains silver nitrate and phenol, producing a magenta colored stain used for skin markings

Carfusion

approximately where is CR located on a mantle field?

supra-sternal notch

slant board would most likely be used for what type of patient?

e- chestwall

provided cross-sectional images of internal structures in relation to contour

transverse tomography

planes imaged in MRI

• coronal

• sagittal

• transverse

• oblique

references that may include natural anatomy or be artificial markers placed internally, at the skin surface, or fixed externally to the patient

fiducial markers

contours must contain what bits of information?

• important bony landmarks

• beam entry points

• line representing the tabletop

• laser marks if available

CT scans used for contouring provide:

• quantitative data for tissue heterogeneity

• delineation of target volume and surrounding normal structures

what is included in doctor’s prescription

• total dose

• dose/fraction

• machine

• energy

• total # of fractions

• treatments per week

• overall time of treatment in days/weeks

• tumor depth

• reference isodose #

• special instructions (e.g., full bladder)

machine that uses a diagnostic x-ray tube on a C-arm that duplicates a treatment unit with respect to geometric properties

conventional simulator

treatment setup with a constant SAD but varying SSD

isocentric

BEV

beam’s eye view

process wherein most of the simulation process can be completed without the patient in the room

virtual sim

commonly used PET scan radionuclides

• Carbon-11

• Nitrogen-13

• Oxygen-15

• Fluorine-18

• Gallium-68

• Rubidium-82

advantages of MRI over CT

• no ionizing radiation

• wider variety of views

• higher contrast

• better imaging of soft tissue

disadvantages of MRI over CT

• lower resolution

• not as good for bones and calcifications

• longer scan times

• smaller magnet hole (aperture)

• fewer contrast agents

most lateral and inferior extension of the temporal bone

mastoid process

located at the medial aspect of the eye where the upper and lower eyelids meet

inner/medial canthus

corresponds to the level of the thyroid cartilage (laryngeal prominence)

C4

first prominent process of the cervical vertebrae

C7

primary purpose/use of bolus

increase dose to skin surface

treatment with the beam (gantry angle) perpendicular to the treatment site

en face

blocking using 1 or 2 HVL’s

transmission blocks

treatment technique wherein one collimator jaw (or MLC set) is moving during beam on, thus progressively shortening the field size in one dimension

dynamic wedging

location between the orbits

nasion

foaming agent used for immobilization

Alpha cradle

process in which transducer converts electrical energy into ultrasound energy and vice versa

Piezoelectric effect

most commonly used axial image database for a 3D treatment planning computer

CT

factor of choice to demonstrate central axis dose at given depth for non-isocentric treatment techniques

PDD

most likely field arrangement for spinal cord compression

single posterior low energy photon field

most likely field arrangement for entire breast treating for patient diagnosed with T1 N1 M0 infiltrating ductal carcinoma

tangential fields with subsequent tumor bed boost

most likely field arrangement for primary brain tumor located int he right temporal lobe

wedged pair consisting of vertex and right lateral field

good method for breast immobilization that often affords the best daily reproducibility

nothing

angle of contralateral breast wedge device

15

areas typically blocked in a mantle field

• larynx (throat)

• humeral heads

• lungs

• spinal cord (AKA cord safety block)

SPECT

single photon emission computed tomography

TNI

total nodal irradiation

term for increased side effects due to all fields not treated in the same day

edge effect AKA tissue lateral damage

STD (in regards to linac)

source to tray distance