Principles of Treatment Planning

Question 1

Where would you find definitions of PTV, GTV AND CTV?

Answer 1

ICRU Report 50

Question 2

GTV:

What does it stand for?

What is it?

Answer 2

• Gross Tumour Volume
• Palpable or visible/demonstrable extent and location of malignant tumour
• i.e. the bit you can see

Question 3

CTV

What does it stand for?

What is it?

Who/what decides it?

Answer 3

• Clinical target volume
• Includes the GTV and the subclinical microscopic malignant disease
• i.e. what area do you want to take to account for the fact that cancer spreads?
• De-Lineated by a clinician/oncologist

Question 4

PTV

What does it stand for?

What is it?

Who/what decides it?

Answer 4

• Planning target volume
• Acknowledges and mitigates against uncertainties in planning and treatment delivery. Ensures the RT dose is actually delivered to the CTV.

Question 5

ICRU 62: ITV

What is it?

Why do we have it?

Answer 5

• Internal Target Volume
• Internal margin to take account of variation in shape, position and size of organs adjacent to CTV which can be caused by:
  
  • Heart beat
  • Swallowing
  • Rectum/bladder filling
  • Loss/gain wieight

Question 6

ICRU 62: Set-Up Margin

What is it?

Why do we have it?

Answer 6

• Variation in patient position
• Dosimetric uncertainties
• Human factors

Question 7

ICRU 62: PTV

What is it?

Why do we have it?

Answer 7

• Planning Target Volume
• Takes into account:
  
  • uncertainties in position
  • dosimetric uncertainties
  • Human factors

Question 8

Treated Volume

Answer 8

Tissue volume that is planned to recieve the dose required to achieve the purpose of the treatment

Question 9

Irradiated volume

Answer 9

tissue volume that recieves dose considered significant in relation to normal tissue tolerance

Question 10

Organ at Risk

Answer 10

Normal tissues who’s sensitivity may significanly influence treatment planning

Question 11

PRV

Answer 11

Planning Organ at Risk Volume

Margin around organ at risk with same function as internal and set-up margins

Question 12

ICRU reference point

Answer 12

• A point that you pick inside the PTV which is representative of the whole PTV. Use this to measure doses to.

Question 13

Max Planning dose

Answer 13

Max dose delivered to a Minimum diameter of clinically meaniingful volume

15mm for large organs

Pretty much the mesh that you divide your dose distribution into

Question 14

Minimum planning target dose

Answer 14

Min dose in PTV

No vol limitation

Question 15

Hotspot

Answer 15

Area outside PTV which recieves more than 100% of specified PTV dose

Question 16

How does DVH look for serial vs parallel organ

Answer 16

DVH has steeper fall off for series organ, i.e. want to prescribe less dose to it because damaging one part of the organ dose more damage.

Question 17

Lmitation of DVH

Answer 17

No spatial information

Varion of matrix size = variable data for same plan