IGRT

Question 1

What is Image Guidance

Answer 1

• Not the delivery of dose
• Used to ensure QA and to check no movement has occurred
• Most tumours are radioresistant if they are not in the treatment beam

Question 2

Key features of IGRT

Answer 2

o Availability of high-quality imaging in the equipment in the treatment room
o Ability to visualise the target (not just external markers or bony anatomy) with the patient in treatment position
o A protocol to act on the findings
 This could be done on-line, i.e., prior to turning the radiation beam on, or off-line between fractions if more complicated decision-making is required

Question 3

Offline IGRT matching

Answer 3

taking image within certain amount of tolerance and review following treatment

Question 4

Online IGRT Matching

Answer 4

taking image while the patient is still on the treatment couch

Question 5

Workflow of IGRT

Answer 5

o Take images 3 consecutive days at the commencement of shift
o Average shifts to account for systemic setup error
o Apply average displacement to the isocentre shifts and this becomes the new isocentre
o Image on Day 4 to confirm Image weekly and if images are beyond threshold action level, repeat each day until a trend is observed or they are within threshold tolerance for two consecutive days

Question 6

Difference between inter-fractional vs Intra-fractional

Answer 6

• Inter-Fractional  varies day to day (e.g., prostate)

- Intra-Fractional  varies within the same day (e.g., lung)

Question 7

Role of IGRT on Motion management

Answer 7

• IGRT facilitates the detection and management of exceptional deviations
  o Including emergent or spurious changes, such as gross positioning errors, weight loss, substantial organ deformations, systemic changes in internal organs, changes in respiratory motion

Question 8

Skin render

Answer 8

• Important of every plan that many RT’s do not value highly enough
• Skin render or images of the field position on skin generated from the planning system is one of the most important steps that should be checked everyday. Prior to imaging.

Question 9

Transponder

Answer 9

• Magnetic implants allow for target delineation without ionising radiation both for setup and also for live tracking during delivery of treatment

Question 10

Rules of matching anatomical points

Answer 10

• Match at least 3 structures within the field outlined

Choose the most stable features

Question 11

Respiratory Gating

Answer 11

• Machine measures peak volume and peak expiration to determine when to turn beam on and off
• Can sometimes assist with beam regulation

Question 12

DIBH

Answer 12

Deep Inspiration Breath Hold

- Camera watches box sitting on the chest of the patient (if moves, beam is turned off)

Question 13

What is EPI

Answer 13

Electronic portal imaging

Question 14

Methods of using IGRT

Answer 14

Original diagnostic Imaging
• Simulation scanning on CT
• Image fusions MRI, PET/CT, SPECT
• DRR Digitally reconstructed radiograph
• MV epi
• kV epi
• CBCT (Cone beam computed
tomography)
• Ultrasound
• Transponders (magnetic implants)
• Fiducial markers (Gold seeds)
• Respiratory Gated breathing
• Active breathing control (Compression)
• Surface tracking (Surface Guided
Radiation Therapy)
• MR-Linac

Question 15

What is ITV

Answer 15

Internal Target Volume

Is the volume encompassing the CTV, which takes into account the fact that the CTV varies in position, shape and size