2D versus 3D imaging

Question 1

Surface Guided Radiation Therapy:
how does it work

Answer 1

-reference DDR/CT given from planning CT
-image acquired on treatment machine is matched to the referenced image

Question 2

features of 2D images

Answer 2

-aka planar imaging
-can be Kv or Mv
- can either be a single or a orthogonal pair

single example= 2D Kv Ant image
orthogonal pair= 2D Kv orthogonal image (Ant and Rt Lat)

Question 3

2D images:
Kv v Mv

Answer 3

-kV x-ray tube and image detector attached to machine (0.01-0.1 cGy per film)

-uses Mv from gantry (1-5 cGy per film)

Question 4

Kv images:
used for
how many surrogates needed

Answer 4

-bone
-3

Question 5

2D KV reference Image vs. 2D KV AP Image

Answer 5

-generated from CT planning - set up field
-Create DRR

-acquired on Linac
-You can specify jaw size – image enough to see anatomy

Question 6

paired Kv image

Answer 6

aka orthogonal fields
one ant image and one right image to allow all 3 translations (longitudinal Lateral and vertical)

ant image for long(sup and inf) and lat (right/ left)
right image for long and vertical direction

Question 7

3D Image Acquisition – Volumetric Imaging
features

Answer 7

• KV is more common
  -Rotates collecting a series of planar images(150-600 in a single or partial arc) then recontructed to create a 3D image

Question 8

patient characteristic that impact scatter dose?

Answer 8

-patient size
-tissue homogeneity
-motion artefact

Question 9

machine hardware that impact scatter dose

Answer 9

-acquistion time
-scan length
-filters used (permanent anti scatter filter built into detector panel) + (Filter (e.g. bow-tie) added to source panel)

Question 10

Sequence following CBCT Acquisition

Answer 10

-day 1= set clip box
-bony match using auto match function
-CHECK AUTO MATCH
-smaller and finer adjustments to soft tissue match using manual match using split screen
-check bladder , rectal volume and body contour

Question 11

what is a clip box

Answer 11

-region of interest used for auto match purposes
-algorithim will match structure only in clip box

Question 12

use of bony match

Answer 12

first performed to help give a “ball park” position and to correct
gross errors

Question 13

use of soft tissue match

Answer 13

used for finer and smaller adjustments

Question 14

what you will see in a 2D MV planar image pt1

Answer 14

-single exposure (planned treatment field ) OR double exposure ( planned treatment field and open field)
-field aperture (field size and MLC displayed) *this is only for 3DCRT not IMRT plans

Question 15

what you will see in a 2D MV planar image pt2

Answer 15

-good soft tissue definition - less bone definition
-image acquired is registered (overlayed) on DRR

Question 16

what is a DRR

Answer 16

2D version of an image produce by a 3D system

Question 17

what you will see in a 2D KV planar image pt1

Answer 17

-no tx field aperture (RT defines the size of area imaged)
-sufficient anatomy to match confidently
-No MLC or field aperture

Question 18

what you will see in a 2D KV planar image pt2

Answer 18

-good bone definition-no soft tissue definition
-image acquired overlayed on DRR

Question 19

what you will see in 3D imaging

Answer 19

-CBCT
-volumetric info (internal anatomy) such as OARS , target volumes and external body contours
-CBCT is registered on CT planning scan

Question 20

For prostate RT - recommendations

Answer 20

-daily on-line imaging is the gold standard
- soft tissue match for 3D
-fiducials for 2DKV orthogonal or 3DCT

Question 21

2D KV Orthogonal imaging vs 3D CBCT

Answer 21

-prostate can be seen on CBCT, not on 2D KV orthogonal
-bladder and rectal volumes can be seen on CBCT
-2D imaging= lower dose and image acquisition quicker
HOWEVER CBCT IS INDICTATED