the tx process preparation process

what are the 4 important anatomical patient data that should be collected for treatment planning

patient surface contour, target volumes, organs at risk, inhomogeneities

where can you get data acquisition from

a ct scan

where is field size defined at

distance of the rotational axis of the machine

where is another point that field size is defined by with isodose lines

intersection of the 50% isodose line and the surface

how is geometric field size defined by

light field

what is penumbra

region on either side of the light field

what isodose lines does penumbra dose range from

80-20%

what are 3 things that width of the penumbra depend on

size of the radiation source, distance from the source at the distal part of the collimator, and SSD

increase source size = _penumbra

increase

increase in SDD = _ penumbra

decrease

increase in SSD = _penumbra

increase

what is penumbra

region of rapid dose fall off at the edge of the beam

bigger source size = _penumbra

more

is a cobalt 60 or linac target cause more penumbra

cobalt 60 source

why does the central axis not diverge

because it is perpendicular to the source

what is the beam divergence formula

length/2 divided by 100, inv tang

what reduces the dose along central axis in photon beams

flattening filter

what does the flattening filter produce along the central axis of a photon beam

flat beam at specified depth (usually 10cm)

what does symmetry mean

same dose at equal distances from the central axis

what can be directly proportional to distance

magnification

what can using a magnification device allow

fairly accurate measurement of device on image

where must the magnification device be placed

near point where accurate measurement is needed

what is another name for the reference point in ct sim

origin

origin = _

0

which shift is the X shift

lateral

what shift is the Y shift

longitudinal

what shift is the Z shift

vertical

what is the target volume

volume that includes the tumor and its occult spread to surrounding tissues or lymphatics

what does GTV stand for

gross tumor volume

what is the GTV

volume of known disease

what can GTV often be identified on

CT images

what can GTV contain

tumor, nodes, or mets

what happens to the GTV if tumor is removed

no more GTV

what does CTV stand for

clinical target volume

what does the CTV contain

GTV and subclinical microscopic disease that may not be visible or palpable

who makes the CTV estimation

physician because you cannot know for certain where this boundary should end

what would the CTV be enclosed by

treatment isodose line

what can untreated or inadequately treated CTV lead to

local failure

what does PTV stand for

planning targeting volume

what is the PTV

geometrical volume containing GTV and CTV

which volume is the ultimate target volume

PTV

what does the PTV take all into account

possible geometric uncertanties

what are examples of geometric uncertanties

set up errors, patient/organ motion, set up uncertainties, penumbra

what isodose should the PTV be enclosed by

90% or better

is the PTV often symmetrical

no

what is the overall goal to have around the PTV

95% isodose line

what does AAPM stand for

american association of physicists in medicine

what is the treatment planning goal

treat the right target volume conformally with the right dose distribution and fractionation

what are some challenges of treatment planning goal

organ movement, positional uncertainty, availability of technology/equipment, and expertise of staff

when is the virtual simulation done

from the CT images performed without the patient being presented

what is virtual simulation

tx fields are defined using CT images and tx unit geometric function

what does DRR stand for

digitally reconstructed radiographs

what form the basis for CT simulation

DRRs

what will be identified on each CT slice

PTV and critical structure

what may be edited as needed to avoid critical structures in tx planning

field shapes and positions

what is contouring

outline structures and volumes

what is another name for contouring

organ segmentation

when can segmented structures are commonly used

field shaping, positioning, and in isodose evaluation

what is image fusion

CT dada set is combined with MRI or PET imaging data

how are translational errors corrected

shifts of lateral, longitudinal, and vertical

what are rotational moves

pitch, yaw, roll