Treatment Uncertainties

Question 1

Anatomic uncertainties

Answer 1

Refers to the clinically suspected but undetected disease involvement

• regional lumps
• microscopic extensions of the disease

Question 2

Geometric uncertainties

Answer 2

Refers to the small uncertainties associated with targeting

Can be classified by their source
-variations in patient anatomy and in patient set up

Can be classified by when they occur
-interfractional and intrafractional

Question 3

Interfractional

Intrafractional

Answer 3

Changes that occur between fractions (so different days)
-bladder filling, immobilization devices

Changes that occur during treatment, within the same fraction
-breathing, patient movement

Question 4

CTV

Answer 4

Clinical target volume
Accounts for anatomic uncertainties
Accounts for microscopic disease and subclinical

Question 5

PTV

Answer 5

Planning target volume
Geometric uncertainty
PTV = CTV + margin

Question 6

Internal margin

Answer 6

Expected physiological movements
Heartbeat swallowing
Patients coordinate system

Question 7

Set up margin

Answer 7

Accounts for uncertainties in patient set up

The treatment machine coordinate system

Question 8

Plan evaluation

Answer 8

-5% and +7% of the prescribed dose is acceptable