ICRU 50, 62, 91 Flashcards
defines treatment volumes
GTV, CTV, PTV, OAR, treated volume, and irradiated volume
-treated volume is usually enclosed by 95% iso curve
-irradiated volume usually gets 50% iso
what does ICRU 62 introduce?
-internal and setup margins for PTV
-defines PRV (planbning risk volume)
-introduced conformity index
-introduces ITV
ITV= CTV+IM
PTV= ITV+SM
-discusses systematic vs random errors
-parrallel vs serial organs
-acceptable dose heterogeneity is 7% to -5% of prescribed dose
-report Dmax, Dmin, Dmean, dose to ref pt
ICRU 62 hot spot
gets > 100%
only significant is min diameters exceeds 15 mm
ICRU reference pt requirements
-dose at pt is clinically relevant
-point should be easy to define in clear and unambiguous way
-pt should be selected so that the dose should be accurately determined
-no steep dose gradient
ICRU83
-for IMRT
-revised classification of treatment volumes
-dose prescription based on DVH
-new definitions of min and max dose
-new surrogate of ICRU pt (don’t use ref pt)
-request for patient specific QA
-new criteria for treatment accuracy
ICRU83 definition of volumes
Because delineation of a GTV may vary according to the diagnostic
modality (e.g., clinical examination, anatomic imaging, functional
imaging) used, a clear annotation is required.
* For example:
* GTV-T (clin, 0 Gy) : tumor GTV evaluated clinically before the
start of the radiotherapy;
* GTV-T (MRI-T2, 30 Gy) : tumor GTV evaluated with a T2-
weighted MRI scan after a dose of 30 Gy of external beam
irradiation
remaining volume at risk
RVR = difference between the
volume enclosed by the external
contour of the patient and that of
the CTVs and OARs on the slices
that have been imaged.
ICRU levels of reporting
Level 1: minimum standards, inadequate for IMRT
* Level 2: standard level
* Level 3 : homogeneity, conformity and biological
metrics and confidence intervals.
ICRU 83 Dmax and Dmin reporting
Reporting of minimum dose should be replaced by the betterdetermined near-minimum dose D98 %,
also designated as Dnear-min.
* Other dose-volume values, such as D95 %
, may also be reported but
should not replace the reporting of D98 %.
* Analogously, it is recommended to report the near-maximum dose
D2 %
as a replacement for the “maximum dose”.
* Both recommendations serve the same purpose, to report a dose
that is not reliant on a single computation point.
Level 3 reporting
-still under development
-includes TCP, NTCP, EUD
dose homogeneity formular
(D2%-D98%)/D50%
The ICRU previously recommended that the dose values in the PTV
be confined within 95 % to 107 % of the prescribed dose.
* With IMRT these constraints may be unnecessarily confining if the
avoidance of normal tissue is more important than target dose
homogeneity.
summary of ICRU 83
More emphasis on statistics
* Prescribing and reporting with dose-volume
specifications
* No longer use ICRU-Refrence Point
* Need to report median dose D50%
* Use model-based dose calculations
* Include the effect of tissue heterogeneities
* Report dose to small mass of water, not dose to
tissue
ICRU 91
This Report covers fundamentals of small-field dosimetry, treatment-planning algorithms, commissioning, and quality assurance for the existing delivery systems, as well as the role of image guidance during delivery
what did ICRU91 introducce
-paddock conformity index
dose reporting recommended by ICRU 91
D50%
D2%
D98%
