ICRU

Question 1

Key features of reference point

Answer 1

• Clinically relevant and representative of the dose throughout the PTV
• Easy to define in a clear way
• Selected where the dose can be physically determined
• Selected in a region where there is no steep dose gradient

Question 2

PRV

Answer 2

planning organ at risk volume
Margins added to OAR to account for variations and uncertainties during treatment
More clinically relevant for serial structures

Question 3

Overall aim of plans

Answer 3

PTV treated with at least 95% of prescribed dose
spare as much normal tissue as possible
keep OAR within limits
Ensure treatment is reproducible

Question 4

Purposes of ICRU

Answer 4

A. Clear, well defined unambiguous concepts
B. Common language
C. Same terminology for prescribing and reporting
D. Defining the AIM of treatment, e.g. Radical or palliative or non-malignant disease

Question 5

PTV dose

Answer 5

95% - 107%
100% is ideal but not possible
97-98% is seen to be optimised

Question 6

Features of good plans

Answer 6

Field sizes - large enough vs small enough
• PTV – Homogeneous
• + 7%/-5% of the 100% or prescribed dose.
• Maximum doses should be within the PTV
• Sensitive normal tissues - marked on plan
• Dose to sensitive structures kept to a minimum
• Treated volume dose larger than dose to surrounding
tissue
• Plan achieves the treatment aim, radical or palliative

Question 7

Gross tumour volume

Answer 7

denotes the demonstrated tumour ie … the gross palpable or
visible/demonstrable extent and location of malignant growth.

If the tumour has been removed, there is no GTV

Question 8

CLINICAL TARGET VOLUME (CTV)

Answer 8

denotes the demonstrated tumour (when present) and also

volumes with suspected (subclinical) tumour. The CTV is a purely anatomic-clinical concept.

Question 9

INTERNAL TARGET VOLUME (ITV)

Answer 9

is the margin given around the CTV to compensate for all

variations in the site, size and shapes of organs and tissues contained in or adjacent to the CTV.

Question 10

PLANNING TARGET VOLUME (PTV)

Answer 10

consists of the CTV(s) and a margin to account for variations
in size, shape and position relative to the treatment beam(s). The PTV is thus a geometric concept
used to ensure the CTV receives the prescribed dose.

Question 11

TREATED VOLUME

Answer 11

is the volume that receives a dose that is considered important for local cure or
palliation

Question 12

IRRADIATED VOLUME

Answer 12

is the volume that receives a dose that is considered important for, or
significant in relation to, normal tissue tolerance

Question 13

What is PTV comprised of?

Answer 13

1. GTV
2. CTV
3. Internal margin (inter and intra fraction variations)
4. Set up margin

Question 14

Clinically significant maximum

Answer 14

a volume is considered clinically

significant if its minimum diameter exceeds 15mm

Question 15

Hot spot

Answer 15

A HOT SPOT represents a volume outside the PTV
which receives a dose larger than 100% of the
specified PTV Dose

clinically significant only if the
minimum diameter exceeds 15mm

Question 16

3 classification of organs at risk

Answer 16

Serial - spinal cord, parallel- lungs, serial-parallel- heart

Question 17

Serial structures requirement and why

Answer 17

Avoid these

• MUST be kept below the tolerance dose

Question 18

Parallel structures

Answer 18

• Minimise volume being treated

* Dose permissible related to volume being treated