TomoTherapy, GammaKnife, CyberKnife Flashcards
How does TomoTherapy deliver radiation?
Helical manner using narrow fields
What are the main characteristics of a tomotherapy unit?
6MV unflattened beam
One set of jaws limited to 3 field lengths
Binary multileaf acting as a field width delimiter
MVCT at 6rpm
Helical tx up to 4rpm
Tx beam-on time approximately 4 to 14 minutes
Gantry rotation and couch movement synchronised
What are the most and least important sources of radiation in TomoTherapy bunker design?
Most important
Leakage
Scatter from pt
Primary source
Least important
What shielding advantages are there over a linac in a TomoTherapy unit?
no FF to cause scatter outside the field
Less head scatter from narrow fields
10cm thick lead beam stop behind the radiation detector
How does the MLC leakage compare to a linac?
There is very low MLC leakage with a Tomotherapy unit
How are patients aligned/setup in a TT unit?
MVCT images can be registered with the kVCT
Give an example of an advantage of MVCT over kVCT
There are no artefacts from for example dental work or protheses with MVCT but they can be considerable with kVCT
How do TT dose distributions compare to other IMRT tx systems?
They are comparable if not better
What advantages are there of TT?
IMRT tx are quickly delivered
Simple to use
Excellent dose distributions
Treatments can be adapted to suit changing circumstances
MVCT is used for IGRT allowing excellent assessment of dose distribution and few artefacts
Overall accuracy of dose delivery is <5%
What is the radiation source for Gamma Knife?
Cobalt 60 sources
How are treatments planned with GK?
Inverse planning
How is patient immobilisation achieved with the GK?
Stereotactic frame - good for SRS, used on MRI, CT and GK. How to relocate in future #s?
Removeable frame: plastic studs for it to be re-attached to.
What are some GK disadvantages?
HASS regulations involved
Source replacement every 4 years takes 2-3 weeks
Limited to H&N tx
Largest tx volume is 30mm diameter
What are some TT disadvantages?
Well-controlled air con is essential
Protection required for leakage radiation is large
Smallest tx volume is 12mm
Regular (simple) QC
What are some GK advantages?
Needs much less radiation protection that old style cobalt bunker Minimal control area Smallest tx volume of around 4mm Minimal QC Minimal repairs
What is the CyberKnife system?
Robotic system Linear accelerator providing a 6MV beam Non-invasive Stereotactic RT High dose beams
What are the main components of the CK?
Manipulator Linac Collimators Imaging system (kV IGRT) Couches Tx planning
Roughly what is the range of field sizes that the CK can treat?
5mm to 60mm
Describe the dose distributions achieved with CK.
Highly conformal
NOT necessarly homogeneous
Normalised to 80% so dose in PTV can vary by 20%
How is data verified from the CK?
- Single beam plans are created for certain collimators to be compared with measured data.
- Penumbras, output factors and dose points are compared.
- Diode-measured PDD in solid water for 60 iris vs Multiplan calculated plan
- Film depth dose measured in solid water compared to Multiplan calculated
What sort of tracking can be used with a CK?
Skull Spine Fiducial tracking Respiratory Lung - track the tumour
For CK tx, how is the pt set up?
Alignment centre selected at start of planning
33 pairs of 2D DRRs generated
Tx room has fixed imaging centre for image guidance system
Pt aligned to imaging centre by comparing x-rays to DRRs
How is the pt position tracked during tx with CK?
Tracking happens throughout the tx
The robot can correct for some movements
What sort of tx parameters are used with the CK?
e.g. no. beams, tx times, no. MU
70 to 250 beams per #
25 to 120mins tx
Around 10,000 MU/#
