Advanced IGRT

Question 1

Define a Systematic Error

Answer 1

Deviation occurs in same direction and similar magnitude of error occurs each fractions (same errors occur)

Question 2

Define a Random Error

Answer 2

Deviation that can vary in direction and magnitude

Question 3

Key Features of IGRT

Answer 3

Availability of high quality imaging equipment in the treatment room

Ability to visualise the target (not just external markers or bony anatomy) with the patient in treatment position

A protocol to act on the findings (a. could be done on-line, prior to beam-on) (b. could be done off-line between fractions, if more complex decision making is required)

Question 4

Why do we perform IGRT?

Answer 4

ALARA

Organ Motion

Tumour Shrinkage

Question 5

Why does kV imaging provide clearer images, when compared to MV imaging?

Answer 5

• kV energy beams result in less attenuation, as energy is better absorbed by soft tissue and bone
• MV energy typically ‘blasts through’ and results in absorption

Question 6

Imaging Modalities (ranked for image quality)

Answer 6

MRI -> CBCT -> kV Imaging -> MV Imaging -> Ultrasound -> EPI

Question 7

Comparison of Dose Requirements for High Contrast Targets and Soft Tissue Targets

Answer 7

Soft tissue targeting required higher dose imaging technique

High contrast targets (bone or seeds) can be accurately visualised at imaging doses as low as 0.1 to 0.5 cGy

Question 8

Comparison between bright and dark components of T1 and T2 MRI

Answer 8

T1: Fat = Bright // Fluid, Calcium = Dark

T2: Fluid = Bright // Muscles = Dark

Question 9

Difference between Interfractional Motion and Intrafractional Motion

Answer 9

Interfractional -> varies day to day (e.g. bladder, rectum, bowel)

Intrafractional -> varies within the same day (e.g., lung, heart)

Question 10

What is the use for Transponders?

Answer 10

Magnetic implants which allow for target delineation without ionising radiation both for setup and live tracing during treatment delivery

Question 11

How much should be contoured for anatomical match structures

Answer 11

At least 3 within the imaging field

Question 12

Structures which can be contoured in the head

Answer 12

Orbital Ridges

Frontal Sinus

Nasal Septum

Maxilla

Question 13

Structures to be contoured in the neck/shoulder

Answer 13

Vertebral Bodies

Base of Skull

Posterior Wall of Trachea

Clavicle

Question 14

Structures to be contoured in the breast

Answer 14

Breast outline

Central lung distance

Central flash distance

Inferior Central margin

Question 15

Structures to be contoured in the lung/chest

Answer 15

Medial edge of rib

Sternum

Carina

Trachea

Anterior Chest Wall

Anterior Edge of Vertebral Bodies

Question 16

Structures to be contoured in the pelvis

Answer 16

Superior pubic ramus

Obturator foramen

Iliac Crest

Vertebral bodies

Sacrum

Pubic Symphysis

Question 17

Is IGRT still important for palliative cases

Answer 17

Verification should be no less rigorous for palliative treatments than for radical treatments

The opportunity to correct an error in palliative treatment may be less due to the shorter fractionation schedule.

Question 18

Application of EPI

Answer 18

Breast

Question 19

Application of KV imaging

Answer 19

head and neck, fiducials

Question 20

application of ultrasound

Answer 20

prostate and breast

Question 21

application of MRI

Answer 21

pelvis, lung and abdomen

Question 22

What is SGRT

Answer 22

Surface guided RT - tracks a patients position before and during treatment