ARRT Radiation Therapy: Protection, Equipment, and QA

kilovoltage peak (kVp)

exposure factor in the diagnostic range controlling beam quality or beam penetrability

controls contrast

as it increases fewer x rays are absorbed by the patient

can increase compton scattering when increased

15% rule

Changing the kVp by 15% has the same effect as doubling the mAs or reducing the mAs by 50% which decreases patient dose

milliampere seconds (mAs)

exposure factor in diagnostic range that determines beam quantity

patient dose follows a direct proportion

controls patient dose more than kVp

protective aprons

made of 0.5 mm of lead

(equivalent to 2 HVL, reduces occupational exposure to 10%)

half value layer (HVL)

the amount of absorbing material that will reduce the intensity of the primary beam to one-half its original value

tenth value layer (TVL)

the amount of absorbing material that will reduce the intensity of the primary beam to one-tenth its original value

3.3 HVL

1 TVL =

collimate

to reduce patient dose during imaging procedures, like KV and MV, do what to the field sizes?

thicker

thicker/thinner cause more scatter

peds patients

exposure time many need to be reduced to reduce patient motion for which group of patients?

mA

to compensate for shorter exposure time, __ may need to be increased which will increase patient dose

radon

varies based on where the person lives, naturally occuring

#1 source of background radiation

cosmic radiation

radiation that comes from the sun and stars

exposure increased with increasing altitudes

type of background radiation?

internal radioactive elements

main source in our body is K-90 which emits beta and gamma rays

type of background radiation?

As Low As Reasonably Achievable

ALARA

time, distance, shielding

most important aspects of radiation protection

shielding

best form of protection in radiation therapy to reduce exposure

10

state and federal regulations require monitoring of anyone who may receive more than __% of the maximum permissible dose (MDP)

records of employee dose

institutions must keep indefinitely

when occupationally exposed workers change employment, exposure records should be transferred to new employment

restricted/controlled areas

supervised by a radiation safety officer

limited to radiation workers

occupational limit of radiation of no more than 1 rem per year (

unrestricted/uncontrolled areas

not under supervision

limited to the general public

cannot receive more than 0.5 rem/year (

radiation area sign

posted in areas where >0.05 mSv/hr at 30 cm from source

high radiation area sign

posted in areas where >1mSv/hr at 30 cm from source

very high radiation area sign

posted in areas where >5 Gy/hr at 1 m from source

caution: radioactive materials sign

posted in areas where sources of radiation are used and/or stored (ex: I-131)

specific and sensitive

low levels of radiation detection devices should be:

primary barrier

directly hit by the useful part of the beam

concrete

most common and cheapest barrier

2 meters

average thickness of a primary concrete barrier

1 meter

the average thickness of a secondary concrete barrier

secondary barrier

hit by scatter or leakage radiation

heat and burn the patient

interactions between biomedical implants and the MRI RF coils can cause the device to

fill out a pre-mri screening form and an interview

prior to the MRI the patient must (2 things)

MR safe

nonferromagnetic or weakly ferromagnetic materials are considered

medical equipment must be labeled with this

aneurysm clips

can be made of pure titanium, elgiloy, MP35N, are MR compatible

neurostimulators

patients with implanted ___ should not have an MRI performed

newer devices that are MR safe for only MR's with 2T or less

implantable spinal fusion stimulators

MR safe

must have radiograph performed prior to ensure leads are not broken (cause burning)

1.5T or less

implantable drug infusion pumps with magnetic switches

not MR safe

heart valve prostheses containing metal

MR safe

ocular implants

not MR safe

radiographs of orbits should be performed prior to MR to determine metal presence

dental implants

MR safe

except those with magnetically activated peices

cochlear implants

not MR safe due to damage to the device

vascular access ports and catheters

MR safe if made of stainless steel, titanium, silicone, or plastic

IV stents, filters, coils

made of non magnetic material and are MR safe

breast tissue expanders and implants

not MR safe

penile implants

not MR safe

welders, metal workers

profession where the risk of metal in the eye can occur leading to blindness if MR is performed, radiograph is needed prior to MR

pregnancy

should only be performed on this group when other diagnostic studies are not sufficient

tattoos

patients with ___ can experience skin reaction including tingling sensations, skin irritation, swelling, heating, burning

can cause image artifact

missle effect

ferromagnetic object is throw into MR system

handling and disposal of radioactive materials

ALARA, PPE (forceps, gloves, gown, mask)n needed when

nuclear regulartory commission

regulates the safe use of radioactive materials and protects the public health in regards to radioactive materials

department of transportation

regulate the transportation of hazardous radioactive material

environmental protection agency

regulates the removal, storage, and usage of nuclear waste

klystron, waveguide, circulator, cooling system

the drive stand contains four parts:

water cooling system

prevents the linear accelerator from overheating

gantry, collimator, and couch

three parts of the linear accelerator that move around isocenter

power supply

provides direct current tot eh modulator

modulator

powers the microwaves source and electron gun

microwaves

is injected into the waveguide to accelerate electrons

klystron

amplifies microwaves

used for energies above 12MV

magnetron

generates microwaves

low energies

circulator

stops microwaves from being reflected and reentering the klystron

located between the klystron and waveguide

electron gun

generates electrons and sends them into the accelerator

made of tungsten

accelerator structure (wave guide)

tube where electrons flow to the gantry under a vacuum

copper tube

uses microwaves from klystron to accelerate electrons to the target

contains SF6 to prevent arcing

positioned horizontally for higher energy production

magnent system

used to bend electrons 90 to 270 degrees to aim towards the target

270 creates a more confined beam

treatment head

where the beam is formed and beam output is monitored

target > primary collimator > beam flattening filter > ion chambers > secondary jaws

photon therapy linear accelerator components

flattening filters

made of lead tungsten uranium steel or aluminum

photon therapy

ion chambers

small chambers located in path of radiation beam and check the beams dose rate and symmetry

target > primary collimator > beam scattering filter > ion chambers > secondary jaws

electron therapy linear accelerator components

scattering foil

made of lead

spread out 3 mm pencil electron beam into larger area

volumetric

CT scanner obtains (volumetric/geometric) images of the patient, which are then used for tx planning

rotating x ray tube with a fixed ring of imaging detectors

internal components of CT scanner

controls for couch movements, gantry tilt, emergency off buttons, lasers

external components of CT scanner

helical

current CT scanners utilize ___ scanning, continuous x ray rotation while the couch moves

larger (70-85 cm)

CT scanners for therapy have a smaller/larger bore size than diagnostic

ionization chamber

gas filled chamber with two electrodes with an applied voltage and a meter that measures the electrical signal

measures the production of rad therapy equip

most common way to measure output

inc/direct

ion chamber:

larger chamber has dec/inc sensitivity?

exposure is in/directly prop to the current?

temp, pressure, volume

when calibrating the ionization chamber, certain correction factors are needed (3) to cause ionizations

pocket dosimeter

tyoe of ion chamber that is low energy personnel dosimeter

cutie pie

Ionization chamber-type portable survey meter

farmer chamber

type of thimble chamber

used to calibrate external beam radiation machines

Geiger-Muller detector

portable instrument used to detect radiation of low levels and radioactive contamination

very sensitive, not dose measuring

used to locate misplaced sources

thermoluminescent dosimeter

made of lithium fluoride

electrons are released and visible light photons are emitted when they are excited by heat

commonly used for in vivo measurements to record entrance or skin dose

optically stimulated luminescence

made of aluminum oxide

electrons are released and visible light photons are emitted when they are excited by light

most common detector used to measure occupational (personal) exposure

diodes

solid-state detector

sensitive

real-time reading

equipment of choice for patient dosimetry

used for a daily QA check on LA beam output

neutron detectors

important in proton and photon therapy above 10 MV

ionization chambers can be used to detect

boron trifluoride (BF3)

proportional counters are used for neutron dosimetry are filled with what gas?

door interlock

radiation beam is unable to turn on when tx room door is ope

daily functional check

collision interlock

stops motion of gantry when too close

daily functional check

laser guard interlock

checked monthly

electron applicator itnerlock

checked annually

safety lights

outside the treatment room

checked daily (at the console and door)

the light bulb can be burned out, the reason for malfunction

emergency off button

terminate the radiation beam and shut down the machine

checked monthly

laser alignment

can affect geometric parameters

daily functional check

must intersect at iso

2 mm

non imrt tolerance

1.5 mm

imrt tolerance

1 mm

srs/sbrt tolerance

40 +/- 5 C

temperature of the waveguide should be