4. Image Guidance and Motion Management Flashcards
List the IGRT roles
- Cancer diagnosis
- Staging
- Delineation
- Treatment simulation and planning
- Patient setup
- Tumour localization
- Motion monitoring
- Treatment response assessment
- Efficacy evaluation
List 4 causes of tumour motion
- Voluntary (body shift)
- Involuntary (respiratory, cardiac, digestive)
- Disease related (weight, tumour)
- Radiation induced tumour shrinkage
List the features of MV imaging
- Based on beams eye view
- Compton interactions dominate
- It is proportional to electron density
- Electron density varies little in the body
- Focal spot is 1mm (decreased spatial resolution)
- Uses treatment source on Linac
- EPID (electronic portal imaging device)
What are the features of kV imaging?
- It is 90 degrees to the treatment beam
- Interactions dependent on photoelectric effect
- Differential absorption
- Related to Z cubed
- Anywhere on the X-ray tube is used
- 1 flat panel imager
T or F
kV enhances bone view and MV enhances air cavity
True
What are the 6 degrees of freedom in modern linacs?
- Vertical
- Longitudinal
- Lateral
- Pitch
- Roll
- Yaw
List 5 volumetric imaging methods
- kV CBCT
- MV CBCT
- In-room CT
- Linac CT
- CT on rails (helical CT)
- MR Linac
What is a vital advantage of using MV CBCT
Reduction in artifacts
NB: Disadvantage is reduced soft tissue contrast
MAR =
Metal artifact reduction
What is the function of bow tie filters for cone beam?
To attenuate radiation to get a better image
What is the main advantage that CT sim has over Cone Beam CT?
Cone beam has more scatter due to lack of collimators and therefore, poorer contrast resolution
What causes geometric distortion in MRI?
Nonuniformity of magnetic field strength
MRI voxels may be converted to _____ via algorithm for electron density
CT number
T or F
Planning CT images are 3D and DRR images are 2D
True
What is image registration and fusion?
The process of determining the geometric transformation that relates identical (anatomic) points in two image series: a moving dataset, and a stationary source dataset
What is Deformable Image Registration (DIR)?
This involves the estimating of the geometric transformation between two images to map them onto a common coordinate system
Deformations =
Shrinking or stretching
Rigid transformation =
Translation and rotation
What is image registration?
Geometrically overlaying images
T or F
Image fusion and registration are sometimes used interchangeably
False
What is image fusion?
Combining different imaging data into a single combined view after they have been registered
List the 4-step process of image matching
- Reference image is obtained from planning (this represents the optimal patient position)
- Images taken at the time of treatment are registered/matched to the reference image
- Variations are identified; corrections are calculated and applied
- Corrections are either manually done or automatic robotic couch
What is the main goal of stereotactic RT?
To treat with larger biologically effective radiation doses
List 5 requirements for Stereotactic Irradiation
- Small target
- Sharply defined target
- Accurate RT delivery
- Highly conformal
- Exclusion of sensitive structures
List the various ways that help to achieve SBRT on a linac
- MLCs
- Intensity modulation
- Inverse planning algorithms
- Precise treatment couch (6DoF)
- Highly stable isocenter
- Cone beam CT
- Patient monitoring
- Respiratory gating and tracking
- QA treatment plan to ensure the “tightness” of the isocenter
What is the CyberKnife?
A mini linac on a robotic arm
The term “EPID” refers to_____
An MV flat panel image receptor
When image matching with a kV imager:
Match to the designated surrogate structure
The goal of IGRT is to:
Treat the patient as precisely as possible
Daily imaging on a linac with a kV x-ray tube will:
Correct inter-fractional motion
Linacs with on-board imager (OBI) are capable of:
- Radiographs
- Fluoroscopic images
- Cone beam CT images
Name the reasons why motion management is needed
- To lower doses to critical structures like the heart and lungs (decreasing rates of pneumonitis and cardiac issues)
- To overcome the problem of intrafractional breathing motion and interfractional tumour and anatomical changes
- To prevent under-coverage of target and overtreatment of OARs
What organs/structures are affected by respiratory motion?
- Lungs
- Breasts
- Esophagus
- Liver
- Pancreas
What is the average number of respirations per minute?
12 to 16
List 5 solutions for motion during RT
- Motion encompassment (during treatment planning)
- Respiratory gating
- Breath-hold
- Motion mitigation (abdominal compression/immobilization)
- Tumour tracking
What is Slow CT?
This involves scanning using a slow gantry rotation speed to capture tumour motion during each slice acquisition
Describe Respiratory Gating
Normal breathing of patient during treatment but treatment is turned on or off based on breathing position
What is the function of a spirometer during a DIBH or MIBH?
To measure and monitor the patient’s lung volume and breathing pattern in real time.
What anatomy are matched for DIBH planning?
- Spine
- Coracoid process
- Mid rib
- Inferior humeral head
- Medial humeral head
During what phase of breathing is gating done?
Expiration phase
T or F
Fluoroscopy is used to track tumour in real time
True
