Principles of Radiotherapy 3 Flashcards
what is a DVH
Graph of dose recieved by rendered 3d volumes as a percentage
-> helps guide planning process using 2D data on monitor
what is set up position of dose
100%
normalised to isocentre
how much dose should the PTV be covered by
95%
Whats the maximum dose ptv can recieve
107%
what unit is absolute dose and what is it shown in?
Gray
OARS
what unit is relative dose and what is it shown in?
%
PTV coverage
what are serial organs?
damaging any function subinit
makes the entire organ to fail
spinal cord
rigid dose constraint
What are parallel organs?
if one function subunit is damaged the organ, total function would be reduced but still work
kidneys
generous dose constraint
what does TD%/Y mean?
what probabilty is that side effect may occur or when and how long it is likely to occur?
example: TD5/5
- 5% probability at 5 years that SE may happen
what does VGY<% mean?
% of volume recieve less than GY dose
example: V50<50%
- 50% OF VOLUME RECIEVE THAN 50GY
what does tissue inhomogeneity mean?
beam coming through at different densities of tissue
steep tissue gradient: bone and air
how does forward planning work?
beam parameters chosen/ dose di calculated
resulting dose distribution recieved
final result reached through manutal iterations of step one and 2
how does inverse planning work?
desired distribution and constraints set
dose dis calculated with automatic field dluence adjustment
priorities and constraints optimised
final result reached through partly automated optimisation process
talk about respiratory gating
aim - reduce lung and heart volume in fields
method - breath hold techniques and normal respiration
outcome- minimises lung and heart motion
talk about tracking movement
have markers indicating ptv position
external markers placed on thorax or abdomen
internal markers are implanted radio-opaque markers
-> fiducial markers for prostate or lung
