Photon Dose Distributions

treatment planning

___________________________ is defined as the process by which dose delivery is optimized for a given patient and clinical situation

dose distributions

______________________ are spatial representations of the magnitude of the dose produced by a source of radiation, and describes the variation of dose with position within an irradiated volume

PDD curve (percentage depth dose curve)

_____________________ is a one dimensional representation of the variation of dose

Beam profile

_______________ is a one dimensional representation of the variation of beam intensity and describes the radiation intensity as a function of position across the beam at a given depth

beam profile

_____________ depicts the beam's intensity in a direction perpendicular to the beam's direction

isodose distributions

_________________________ are two dimensional (2D) spatial representations of dose and is a collection of points, all having the SAME dose

isodose distributions

___________________ are the numerical values of the lines represent percentages of the dose existing at a point along the central axis

-Beam energy

-SSD

-field size

What does isodose distributions vary with?

wedged fields

__________________ involves differential attenuation along the varying thickness of the wedge with produces a dose gradient along the wedged dimension of the beam

true

T/F: For wedged fields, less dose exists under thicker portions of the wedge that exists along less thick portions

wedge angle

the angle between the slanted isodose line and a line perpendicular to the central axis of the beam

-beam energy

-SSD

-field size

Wedged fields vary with:

-physical wedge

-enhanced dynamic wedge

What are the methods of created a wedged field?

moving collimator jaw

What does a dynamic wedge use?

open fields

What type of combined field isodose distribution uses multiple fields that are combined to take advantage of the improved dose distribution?

open

A POP field is combined ___________ field

Parallel-opposed field (POP)

________________ is the most common combined field geometry and involves two treatment fields sharing a common central axis, 180 degrees apart

wedged fields

A combined field isodose distribution can create a uniform dose by using two _______________

hinge angles

the angle between two beams' central axes

90=⌀/2

What is the equation for hinge angle?

obliquity/contour corrections

What type of correction is for beam incidence onto surfaces other than flat surfaces and for angles of incidence other than 90 degrees: on SKIN surface

heterogeneity corrections

What type of correction accounts for the presence of irradiated media other than water, like tissue differences within a patient?

False, scatters differently

T/F: Fat, bone, muscle, and air attenuate and scatter the beam similar to what water does

true

T/F: With MV energies, the compton effect is the predominant interaction and the attenuation of the beam in any medium is a function of the electron density of the medium

-power law TAR method

-generalized Batho correction

-equivalent TAR method

-Delta volume method

What are other methods of heterogeneity corrections?

kill the tumor but spare the normal tissue

What is the goal of 3D Conformal radiation therapy?

magnitude of dose and radiosensitivity of the tissue

What are two factors that affect biologic effect?

3D treatment planning

The process by which 3D visualization, dose calculation, and plan evaluation tools are used to produce optimized treatment field arrangements

image, CT

3D treatment planning is ___________ based, and patient anatomy is represented by _______ data sets

target volumes and structures

For both conventional 3DCRT and IMRT the _______________ and critical ______________ are defined

maximize, minimizing

For both 3DCRT and IMRT the beams are arranged in an attempt to __________ the dose to targets while _________________ the dose to critical structures

IMRT

___________ techniques allow for the modification of the distribution of intensity WITHIN a treatment beam to achieve the stated goal

-Static

-Dynamic

- Fan beam

-Volumetric arc

What are the four methods of IMRT treatment delivery?

forward

___________ planning is used with 3DCRT

forward

What type of planning requires that dose altering parameters and beam modifiers be entered by the planner?

true

T/F: For forward planning, after the initial dose calculation is completed, the planner evaluates the dose distribution and edits the modifiers or other parameters to produce an improved plan, and this process is repeated until an acceptable plan is achieved

inverse

____________ planning is used with IMRT and VMAT

inverse

___________________ planning is the process that calculates dose distributions and creates MLC patterns based on initial dose delivery and avoidance parameters

inverse

_______________ planning involves the dose to be delivered to PTV, contour of critical structures done by planner, then the planning system computes alternative intensity patterns until the best possible solution is determined

treatment planning algorithims

________________________ is the planning systems dose calculation processes; a series of mathematical equations, and their associated input parameters, that produce values of dose as a function of position within the dose calculation matrix

a grid of points at which dose is computed and subsequently displayed

What is the dose calculation matrix?

methodology

Treatment planning algorithms are categorized based on dose calculation ___________________

-data driven algorithms

- model driven algorithms

What two algorithms are based on dose calculations?

2D and 3D

Treatment planning algorithms are also classified according to the dimensionality of the calculation methodology. What are the two different kinds?

Gross Tumor Volume (GTV)

_____________ is the gross palpable, visible, and/or demonstratable extent and location of malignant growth

GTV

_______ is the volume of known disease

False, GTV

T/F: Disease that is visible on a CT scan is a common example of CTV

Clinical Target Volume (CTV)

_________________ is the tissue volume containing the GTV and or subclinical microscopic malignant disease

CTV

__________ includes gross visible or palpable disease PLUS any possible microscopic extensions of disease that may not be visible or palpable

True

T/F: The CTV is the volume that must always be enclosed by the treatment isodose

Planning target volume (PTV)

______________ is a geometric volume, has dimensions believed to always contain the CTV, taking into account all possible geometric uncertainties such as setup uncertainties and patient and or organ motion

treated volume

________________ is the volume enclosed by the isodose surface selected as being appropriate to achieve the purpose of treatment

treated volume

The volume enclosed by the prescription isodose surface is the _____________________

true

T/F: Treatment planning systems have drawing tools that allow the planner to outline structures and planning volumes

organ segmentation

_____________________ is the process of identifying structures, target volumes, or normal tissues by creating contours around them

image fusion

_________________- is the process of combining the images from imaging studies other than the simulation, typically MRI or PET

Beam's eye view (BEV)

________ are images reconstructed from CT data that represents the patient's anatomy and defined volumes from the perspective of the treatment beam

Digital reconstructed radiographs (DRR)

__________ is when a BEV is reconstructed such that diverge-corrected patient anatomy from the CT data set is also included in an image that imitates a radiograph

Room's eye view

____________ demonstrates the geometric relationship of the treatment machine to the patient and allows clear visualization of the entrance and exit of the beam through the patient

Dose volume histogram (DVH)

__________ is a plot of target or normal structure volume as a function of dose

-high percentage volume at prescribed target dose

-rapid decrease in volume beyond the prescribed dose

What are the characteristics of an optimal target volume DVH?