ICRU83 Flashcards
ICRU83 is..
supplement to ICRU62
-gives more detailed recom on different margins
-introduces remaining volume of risk RVR
RVR
when delineating OAR (esp. for IMRT) all normal tissues that could potentially be irradiated should be contoured
image volume within patient (not incl. OAR +CTV)=RVR
3DCRT:
-difficulty
-type of planning
-fluence
-dose
-MU
-ISOCENTRE
-easy
-forward
-uniform
-uniform
-low
-dose defined to volume , spefically at isocentre
IMRT:
-difficulty
-type of planning
-fluence
-dose
-MU
-ISOCENTRE
-complex
-inverse
-non-uniform
-high gradient
-high
-isocentre dose is meaningless
ICRU 83 take home messages
ICRU ref point not used, volumetric prescription instead
ICRU83 vs ICRU 50+62
-previous ICRU report= dose values in PTV are inbetween 95 and 107 of prescribed dose
-BUT w/ IMRT , these constraints maybe confining if avoiding OARs us more important than achieving dose homogenity in target
TF, ICRU83 suggests using D2 and D98 for regions of high and low dose
IMRT PTV DOSE DISTRIBUTION
less homogenuous but more conformal than conventional.
also it can produce absorbed dose gradients
GTV… same def but
specifications needed:
-TNM staging
-mention site + imaging modality
-record any changes during tx to plan during adaptive tx
CTV … same def but
recommend clear annotation used
eg CTV-T+N (CT,35GY)
ITV … same def but
better delineation is possible w 4D imaging
PTV … same def but
-compromising PTV if overlapped with OAR is no longer recommended
-in this situation PTV is subdivided into subvolumes
OAR … same def but
classification is the same (serial , parrallel ect)
PRV… same def but
if overlaps w PTV…
PTV +PRV can be subdivided into subvolumes and be given individual absorbed dose constraint
TV
same def
rationale of RVR
-detects any unsuspected regions of high absorbed dose outside PTV and PRV
-estimates risk of late side effects
Dose reporting:
parameters used
Dmean (D50)
D98.. near min
D95
D2..near max
Dv
Vd
for reporting PTV and CTV , report
Dmean (D50)
D98.. near min
D2..near max
for reporting PRV, report
serial= Dmax/D0 rather than D2%
parallel=Vd (volume recieving atleast the absorbed dose), D mean
serial/ parallel =all 3 parameters
Dose homogenity
characterizes the uniformity of the absorbed dose in TV
D2-D98/D50
if HI=0….. dose distribution almost homogenous
dose conformity
characterizes how high dose regions conform to PTV
due to use of DVH , use of CI and HI are likely to be limited
