mulitmodality Flashcards
pros of CT sim
dose calc from e density data
quick acq time
cons of CT sim
Structural and functional information is superior with other imaging modalities
Common Imaging modalities that you will use in RT
planning
- MRI – structural information
- PETCT – functional information
Incorporation of Multimodality Imaging
Why?
Improves anatomical and functional detail for
delineation
no overestimating TV(excess NT
irradiation tf issues with meeting planning objectives) and no underestimating OARs (DVHs not accurate)
Image registration
Determining the geometric transformation to align anatomical points between ; a moving dataset (MRI OR PETCT) and a stationary source dataset (CT)
Image fusion
combined display of the mapped data from the moving dataset with the stationary
dataset.
Rigid registration — limited to translational and rotational shifts
inaccuracies and may not account for changes in; weight of the patient between scans,
changes in the positioning of the patient,
soft-tissue displacements due to breathing.
Deformable registration
tracks voxel-to-voxel changes from one image to another.
can correct changes in weight ect. by;
mapping between a voxel in one image and the corresponding voxel in a subsequent image.
Issue with deformable registration – moving image is ‘deformed’ to match stationary one. tf actually patients status and difficult to QA
Method 1 Use Diagnostic Images:
Opportunities
-Optimises use of staging and grading images, improving efficiency and avoiding additional appointments or rad expo
-PACS(picture archiving and communication system) =facilitates very swift transfer of images
-TPS can transfer, receive and store large amounts of imaging data , as PET CT has huge amounts data
Method 1 Use Diagnostic Images:
barriers
-diagnostic and not planning intent tf =
Positioning differences ….inacurrate tumour localisation …..poor dose distribution…. Irradiation of normal tissues
-systematic errors = no bladder/rectal prep
possible challenges of image registration
PART 1
Quality: Images can be noisy and of poor quality tf difference in the appearance of the two images
anatomy (internal and external) can differ between scans
labour-intensive and requires manual verification of the quality of the registration by qualified expert
possible challenges of image registration
PART 2
Scan Parameters: Scan parameters of the registered images can affect the integrity and the size of their voxels.
E.g. Spatial resolution of PET images can be lower than CT or MR tf affects recon voxels
Method 2 Acquire a dedicated MR and/or PETCT sim:
opportunities
same position as planning CT
bladder and rectal preparation can be done
tf reducing systematic errors in image registration
Method 2 Acquire a dedicated MR and/or PETCT sim:
barriers
-may need 1-2 extra appointments. Do not want to delay treatment start date – scans must take place in quick succession to facilitate initiating delineation and subsequently planning
PETCT and MRI scan times are longer, hard to maintain poisition
hard to immobilse for PET/CT as ptx is radioactive
Method 3 MR or PETCT only pathway
Opportunities
More efficient – PET CT and MRI images are fully maximised
Less appointments for the patient- convenience and dose
Efficiency in healthcare system - sustainability
Method 3 MR or PETCT only pathway
barriers
-claustrophic – no planning CT to revert to
-MRI and PET CT acquisition can be long
