Introduction to Treatment Planning Module

Question 1

The Planning Process

Answer 1

Pre-planning considerations
Image Registration
target volume delineation
contouring
additional contouring
field set up
Optimisation
Dose Calculation
Plan evaluation

Question 2

Pre Planning Phase

Answer 2

immobilisation (internal and external considerations)
use of contrast

Question 3

Pre Planning Phase: Bolus

Answer 3

-tissue equivalent material that increases dose to skin
-counteracts w skin sparing effect from MV beams

also used for tissue irregularities

Question 4

Image Registration

Answer 4

fusion of multimodality images with the planning CT scan to assits in target and OAR definition

Question 5

OAR Contouring :
impact on
function

Answer 5

-dose calculation and plan quality in dosimetry
-creates dose volume histogram (DVH) info and predicts toxicity

Question 6

OAR Contouring :
requirement for inverse planning optimisation process

Answer 6

IMRT
VMAT

driven by volumes
– Target and OAR relationship
-Competition of planning goals
– Sensitivity in optimisation

Question 7

accurate imaging assists the contouring process

Answer 7

–Decrease in interobserver variability
– DVH calculation
– Greater confidence in predicting toxicity

Question 8

Additional Contouring:
The PTV Eval concept

Answer 8

caused by expansions of CTV
breast
parotid
anus

Question 9

post-void residual measurement PVR

Answer 9

-margin around a OAR to account for positional uncertainties

Question 10

forward planning

Answer 10

place beams in RT treatment planning system

required decisions include :
angles of beams
wedges used or not
MLC configuration will be used to shape the radiation from each beam

Question 11

when is forward planning used

Answer 11

tumour simple shape and not near any critical organs.

Question 12

inversed planning

Answer 12

RO defines critical organs and tumour,
planner then gives target dose and important factors for each

Question 13

Serial Organs
Parallel Organs

Answer 13

loses functionality if one of the sub volumes are damaged eg spinal cord , brain stem

loses functionality if only all sub volumes are damaged eg liver kidney

Question 14

components of field set up

Answer 14

isocentre location
bolus
beam energy
beam aperture
beam orientation
technique
weighting
wedge

Question 15

field setup: isocentre location

Answer 15

geometric centre of PTV

exceptions= half beam block techniques ,mono-isocentric technique

Question 16

field set up
technique

Answer 16

single feild
Parallel opposed
junctioning and mono-isocentric

Question 17

weighting

Answer 17

the relative contribution of beam to overall plan

Question 18

beam Orientation

Answer 18

entry and exit dose has a huge impact on sparing critical structures for 3DCT

less relevant for IMRT

Question 19

Beam Aperture

Answer 19

penumbra
sheilding

Question 20

beam energy

Answer 20

linked depth of penetration ((effective path length)
skin sparing effect and % depth dose curves

Question 21

wedges

Answer 21

tilts isodoses relative to their normal position at central axis

tissue compensator
achieves a uniform distribution in multi field technqiues

Question 22

types of wedges

Answer 22

physical , dynamic and universal

Question 23

what does eclipse TPS use

Answer 23

dynamic wedges:

may need to spin collimator thru 90 degreesin planning to make sure wedge direction is correct

Question 24

Normalisation

Answer 24

point where dose is forced at 100% and dose everywhere is changed by the same ratio
also known as prescription point

plans are generally normalised at geometric centre of PTV

Question 25

The isocentre and norm pt location will differ if

Answer 25

the isocentre is:

at the beam or block edge
in inhomogeneous tissue

Question 26

Plan evaluation
What needs to be considered

Answer 26

target coverage,conformity and homogenity
OAR doses
integral dose
field arrangement
monitour units
treatment time

Question 27

integral dose meaning

Answer 27

the total energy absorbed by the body , the product of mass of tissue irridicated and absorbed dose.

Question 28

monitor unit

Answer 28

measure of radiation beam on time

one monitor units = 1cGy of absorbed dose in water under specific conditions

Question 29

CB-CHOP : plan evaluation

Answer 29

-contours- review target volumes and OARs
-Beam arrangements / Fields - appriopate and reasonable
-coverage-evaluate on graphic plan and DVH
-Heterogenity/hot spots -value and location
-OARs- review specific constraints ,DVH, isolines on plan
Prescription- total dose, dose per fraction and image guidance

Question 30

What is a DVH

Answer 30

graphical representation of the dose-volume relationship inside a pre-determinded volume such as ptv or oar

computer calculates volume of structures that recieves at least the given dose and ploys the volume (or percentage volume) vs dose