TomoTherapy, GammaKnife, CyberKnife

Question 1

How does TomoTherapy deliver radiation?

Answer 1

Helical manner using narrow fields

Question 2

What are the main characteristics of a tomotherapy unit?

Answer 2

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

Question 3

What are the most and least important sources of radiation in TomoTherapy bunker design?

Answer 3

Most important

Leakage
Scatter from pt
Primary source

Least important

Question 4

What shielding advantages are there over a linac in a TomoTherapy unit?

Answer 4

no FF to cause scatter outside the field
Less head scatter from narrow fields
10cm thick lead beam stop behind the radiation detector

Question 5

How does the MLC leakage compare to a linac?

Answer 5

There is very low MLC leakage with a Tomotherapy unit

Question 6

How are patients aligned/setup in a TT unit?

Answer 6

MVCT images can be registered with the kVCT

Question 7

Give an example of an advantage of MVCT over kVCT

Answer 7

There are no artefacts from for example dental work or protheses with MVCT but they can be considerable with kVCT

Question 8

How do TT dose distributions compare to other IMRT tx systems?

Answer 8

They are comparable if not better

Question 9

What advantages are there of TT?

Answer 9

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%

Question 10

What is the radiation source for Gamma Knife?

Answer 10

Cobalt 60 sources

Question 11

How are treatments planned with GK?

Answer 11

Inverse planning

Question 12

How is patient immobilisation achieved with the GK?

Answer 12

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.

Question 13

What are some GK disadvantages?

Answer 13

HASS regulations involved
Source replacement every 4 years takes 2-3 weeks
Limited to H&N tx
Largest tx volume is 30mm diameter

Question 14

What are some TT disadvantages?

Answer 14

Well-controlled air con is essential
Protection required for leakage radiation is large
Smallest tx volume is 12mm
Regular (simple) QC

Question 15

What are some GK advantages?

Answer 15

Needs much less radiation protection that old style cobalt bunker
Minimal control area
Smallest tx volume of around 4mm
Minimal QC
Minimal repairs

Question 16

What is the CyberKnife system?

Answer 16

Robotic system
Linear accelerator providing a 6MV beam
Non-invasive
Stereotactic RT
High dose beams

Question 17

What are the main components of the CK?

Answer 17

Manipulator
Linac
Collimators
Imaging system (kV IGRT)
Couches
Tx planning

Question 18

Roughly what is the range of field sizes that the CK can treat?

Answer 18

5mm to 60mm

Question 19

Describe the dose distributions achieved with CK.

Answer 19

Highly conformal
NOT necessarly homogeneous
Normalised to 80% so dose in PTV can vary by 20%

Question 20

How is data verified from the CK?

Answer 20

• 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

Question 21

What sort of tracking can be used with a CK?

Answer 21

Skull
Spine
Fiducial tracking
Respiratory
Lung - track the tumour

Question 22

For CK tx, how is the pt set up?

Answer 22

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

Question 23

How is the pt position tracked during tx with CK?

Answer 23

Tracking happens throughout the tx

The robot can correct for some movements

Question 24

What sort of tx parameters are used with the CK?

e.g. no. beams, tx times, no. MU

Answer 24

70 to 250 beams per #
25 to 120mins tx
Around 10,000 MU/#

Question 25

Where can dose constraints be found for stereotactic body radiation therapy?

Answer 25

AAPM TG 101

Question 26

What daily checks need to be done for the CK?

Answer 26

Safety checks
Output
Automatic quality assurance
IRIS collimator check

Question 27

What might need to be taken into account given the imaging performed with the CK?

Answer 27

Each image effective dose ranges from 0.02mSv to around 0.3mSv.
Tens to hundreds of images may be taken depending on the site, introducing extra dose to the pt.