Treatment Planning and Verification

Question 1

What is the purpose of patient immobilisation?

Answer 1

• Achieves a reproducible patient position

- Stops patient movement

Question 2

What are desirable characteristics for an immobilisation device?

Answer 2

• Easy to use
• Easy to produce
• Patient comfort
• Resistance to deformation
• Minimal attenuation of the radiation beam for treatment
• Minimal imaging artefacts

Question 3

What is the purpose of tumour localisation?

Answer 3

• To identify the gross tumour volume and clinical target volume
• Identify any multi-focal disease and involved nodes

Question 4

What is the gross tumour volume?

Answer 4

Gross palpable or visible/demonstrate extent and location of the malignant tumour.

Question 5

What is the clinical target volume?

Answer 5

• Includes the GTV and/or subclinical microscopic malignant disease.
• The CTV must be adequately treated in to ensure the intended outcome of the radiotherapy.

Question 6

What does the delineation of the CTV depend on?

Answer 6

Tumour characteristics
Probable invasive capacity
Likelihood of microscopic occult disease.
Anatomical/topographic and biological considerations

Question 7

When might a CTV be defined without a GTV?

Answer 7

At sites with suspected malignant cells (e.g. regional lymph nodes)

Question 8

What is the internal target volume?

Answer 8

CTV plus an internal margin.

Question 9

What does the internal margin depend on?

Answer 9

• Variation in shape, position, and size of organs adjacent to CTV
• Change in size shape and position of CTV

Question 10

What is the planning target volume?

Answer 10

Internal target volume plus a setting-up margin.

Question 11

What does the setting-up margin depend on?

Answer 11

• Uncertainties in patient positioning

- Alignment of radiation beams.

Question 12

What is the treated volume?

Answer 12

The tissue volume that is planned to receive at least the dose selected as appropriate to achieve the purpose of the treatment.

Question 13

What is the irradiated volume?

Answer 13

The tissue volume that receives a dose that is considered significant in relation to normal tissue tolerance.

Question 14

What is an Organ at Risk (OAR)?

Answer 14

Normal tissues whose radiation sensitivity may significantly influence treatment planning and/or prescribed dose.

Question 15

What is the planning organ at risk volume?

Answer 15

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

Question 16

What criteria define a good treatment plan?

Answer 16

• 100% dose at isocentre
• PTV enclosed in 95% iso-dose line
• Maximum dose in PTV no higher than 107%
• Rapid dose fall-off outside PTV
• No significant dose to critical organs

Question 17

What dose specifications must be reported in line with ICRU 50?

Answer 17

• ICRU reference point
• Max dose in PTV
• Min dose in PTV

Question 18

What criteria should guide the placement of the ICRu reference point?

Answer 18

• Dose at point should be clinically relevant
• Dose at point is representative of the dose throughout the PTV
• Easy to define in a clear and unambiguous way
• Selected where the dose may be accurately determined
• In a region with no steep dose gradient

Question 19

What is the maximum planning target dose?

Answer 19

The maximum dose delivered to a clinically meaningful volume (sphere 15mm of diameter for large organs)

Question 20

What is the minimum planning target dose?

Answer 20

Smallest dose in the PTV (no volume constraint)

Question 21

What is a hot-spot?

Answer 21

A clinically meaningful volume outside the PTC which recieved a dose larger than 100% of the specified PTV dose