Tx Volumes & Uncertainty Flashcards
what are 2 ways to make a treatment plan?
field-based and volume-based field designs
anatomical uncertainties (2)
clinically suspected but undetected disease involvement
-regional lymph nodes, microscopic extensions
based on pt anatomy
geometric uncertainties (3)
- spatial uncertainties associated with targeting
- due to lining up, orienting inconsistently
- biological reasons
- isocenter varying between machines
what are the 2 sources of geometric uncertainties
-variations in anatomy and pt setup
what are the 2 classifications of geometric uncertainties in regards to when they occur
interfractional - between
intrafractional - during
how do we account for all the uncertainties when treatment planning?
add a margin
GTV (3)
gross tumour volume
gross demonstrable extent and location of malignant growth
RO will see in imaging and outline
CTV (2)
tissue volume that contains the GTV plus any microscopic extensions
GTV+margin=ctv
what does the CTV account for?
anatomical uncertainties
PTV (4)
planning treatment volume
geometric volume
accounts for geometric uncertainty
CTV+margin=PTV
internal margin (2)
accounts for expected physiologic movements and variations in size, shape, and position of the CTV
position of the CTV in reference to the pt coordinate system
set up margin (2)
accounts for geometric uncertainties in pt set up and alignment of the beams through all sessions
uncertainties in pt beam positioning in reference to the treatment machine coordinate system
CTV+IM
ITV - internal target volume
ITV+SM
PTV
treated volume
the volume enclosed by the prescription dose
