IMRT AND 3DCRT

Question 1

describe 3DCRT

Answer 1

series of computed generated images to create a 3d model of the treatment area.

precise delivery of radiation to the tumor while minimizing exposure to surrounding healthy tissue

however less effective treating tumours with irregular shapes.

Question 2

describe IMRT

Answer 2

delivery of radiation at varying intensities and non-uniform radiation distribution across a field.

allows a more tailored treatment plan as isodoses conform better to PTV

more time consuming to plan, safety checks, and quality control
expensive.

Question 3

fluence heat maps on IMRT

Answer 3

modulated

Question 4

the changing intensity is based on
the modulated fluence DETERMINES

Answer 4

dose DELIVERED

the MLC leaf motion (Sliding window)
or
number and MU output for each segment (Step and Shoot)

Question 5

Increased Control over Dose Distribution with

Answer 5

Ghost structures
Blocking structures
Heaters/Coolers

-encourage the dose gradient around the PTV and control peripheral body dose

Question 6

Additional Planning Contours

Answer 6

Virtual contours used only in optimisation but not plan evaluation.

Question 7

Additional Planning Contours allow:

Answer 7

-improves coverage of whole or partial target
-lessen competition between structures
-smoother or gradual changes in varaition eg PTV
-Control dose homogeneity across a large PTV

Question 8

Mandatory Level of Reporting for IMRT

Answer 8

D98%: The dose that covers 98% of the volume
– Near minimum
D2%: The dose that covers 2% of the volume
– Near maximum
D50%: The median dose as this is not influenced by the ‘tails’ of the DVH

Question 9

Optimisation Process;IMRT

Answer 9

Planner decides on required dose coverage with
dose constraints for surrounding structures

Upper and lower dose limits are to be nominated

Question 10

isocentre placement:IMRT

Answer 10

Not necessary to be in the centre of PTV or even in a structure

Question 11

isocentre placement: 3DCRT

Answer 11

the geometric centre of the PTV
– Exceptions =half beam block techniques

Question 12

Normalisation:
IMRT
3DCRT

Answer 12

-100% at target mean
- at reference point or field isocentre

Question 13

Beam Orientation :
3CDRT
IMRT

Answer 13

-Entry and exit dose has a huge impact on sparing critical structures
-less relevant ,
non-opposing beams
more is not always better