ICRU 83Prescribing, Recording, and Reporting Photon-BeamIntensity-Modulated Radiation Therapy

Anagha S PachatMSc Radiation PhysicsUniversity of Calicut

ICRU 83 The present report is based on conceptsand definitions previously introducedin ICRU Reports 50 and 62.

This provides the informationnecessary to standardize techniques andprocedures and to harmonize theprescribing, recording and reporting ofIMRT.

Why we need this report??

By the evolution of modern technologies conformity of radio therapy techniques has increased

It necessitate extreme care in volume delineation , dose prescription and recording

ICRU83▪ IMRT has large number of degree of

freedom and it use variable intensity beam lets

▪ Manual comparisons of all possible intensity patterns are not practical

▪ Thus some evaluation tools have to be used such as DVH

ICRU 83

▪ In this report the use of DVHs in prescribing, recording and reporting is emphasized▪ The dose-volume histogram ( DVH )

has become a critical tool to evaluate complex 3D absorbed-dose distributions, and its use is even more important for IMRT.

ICRU 83

▪ It is recommended that the dose-volume specifications be used for reporting the treatment plan. The absorbed dose that covers a specified fractional volume V, DV, should be reported. ( For example, D95% is the absorbed dose that covers 95% of the volume).

ICRU83

▪ The report recommends that the median absorbed dose, specified by D50%, should be reported, instead of previously defined dose at the ICRU reference point Dref.▪ D50% – is the absorbed dose received by 50% of the volume, is often a good choice for a representative absorbed-dose value for the PTV.

ICRU 83

▪ The dose-volume metric D100%would be commonly called the minimum absorbed dose.

▪ The minimum absorbed dose might not be accurately determined because it is often located in a high-gradient region at the edge of the PTV, making it highly sensitive to the resolution of the calculation.

ICRU 83

▪ Therefore, reporting of D100% is not recommended because the PTV cannot be determined with sufficient accuracy .▪ Reporting of minimum absorbed dose should be replaced by the better determined near-minimum absorbed dose, D98% , also designed Dnear-min.

▪ Other dose-volumes values, such as D95%, may also be reported but should not replace the reporting of D98%.

ICRU 83

In previous ICRU Reports, it was recommended to report the “ maximum absorbed dose “.

In the ICRU83 Report, is recommended the near-maximum absorbed dose, D2% , as a replacement for the “ maximumabsorbed dose “

It is recommended that D2% also be reported as it is simple to obtain and will add to consistency of reporting.

ICRU 83 Prescribing and Reporting

Historically, the ICRU ( 1993, 1999, 2004 and 2007 ) identified three

levels of prescribing and reporting: - Level 1 - Level 2 - Level 3

ICRU 83 – P & R Level 1

▪ Is considered the minimum standard required in all centers, a standard below which radiotherapy should not be performed

▪ Level 1 is sufficient for treatments and implies that knowledge of absorbed doses on the central beam axis is known and that simple two-dimensional ( 2D ) absorbed-dose distributions at the central axis are available.

▪ Level 1

recommendation

s: minimum

standards for

prescribing and

reporting.

ICRU 83 – P & R Level 2

Level 2

recommendations:

P & R state-of-th

e-art

techniques.

▪ Level 2 prescribing and reporting implies that the treatments are performed using computational dosimetry and 3D imaging. At this level, it is assumed that all volumes of interest are defined using CT or MR and the 3D dose distributions are available and include heterogeneity corrections.

ICRU 83 – P & R Level 2 cont..

▪ It is expected that dose-volume histograms ( DVH´s) for all volumes of interest are routinely computed. ▪ It is also assumed that a

complete QA program is in place to ensure that the prescribed treatment is accurately delivered.

ICRU 83 – P & R Level 3

Level 3

recommendations:

optional research-and-

development reporting.

▪ Reporting at Level 3 includes the development of new techniques and▪ approaches for which reporting

criteria are not yet established . Examples include the use of concepts such as tumor-control-probability ( TCP ) normal tissue complication probability ( NTCP ),

TCP and NTCP TCP is then interpreted

as the probability of tumor clonogens not surviving anywhere in the tumor.

NTCP stands for normal tissue complication probability

TCP follows a sigmoid curve from zero control at some low absorbed dose to certain local control at high absorbed doses

MATHEMATICAL FORMULA

TCP = e-(SF × N) NTCP=1/1+(D50\

D)k

SF=survival fraction k = slope of dose–response curveD = total doseD50 = tolerance dose

The main aim of radiation therapy is to maximize the TCP and minimize NTCP

ICRU 83 – Homogeneity & Conformity

Dose homogeneity characterizes theuniformity of the absorbed-dosedistribution within the target .

Homogeneiy index is defined as,

HI = D2%-D98%

D50%

Dose-volume reporting - D50% (Dmedian), Dose received by 50% of PTV- D98% : Dose received by 98% volume of PTV - D2% : Dose received by 2% volume of PTV

CONFORMITY AND CONFORMITY INDEX

Dose conformity characterizes the degree to wich the high-dose region conforms to the target volume, usually the PTV.

CI=TV/PTV It can be employed when the PTV is fully enclosed by the Treated Volume.

It can be used as a part of the optimization procedure.

Dose conformity characterizes the degree to which the high-dose region conforms to the target volume, usually the PTV.

Examples of low and high dose homogeneity and dose conformity.

ICRU VOLUMES

▪ Delineation of volumes is an obligatory step in the planning process

▪ several volumes related to both tumor and normal tissues have been defined for use in the treatment-planning and reporting processes.

DEFINED VOLUMES ARE

Gross tumor volume or GTV

Clinical target volume or CTV

Planning target volume or PTV

Organ at risk or OAR

Planning organ-at-risk volume or PRV

Internal target volume or ITV

Treated volume or TV Remaining volume at

risk or RVR

Gross tumor volume (GTV)

▪ The GTV is the gross demonstrable extent and location of the tumor.

▪ The GTV may consist of ▪ primary tumor (primary tumor GTV or GTV-T),▪ metastatic regional node(s) (nodal GTV or GTV-N), ▪ distant metastasis (metastatic GTV, or GTV-M)

▪ In case of post-operative irradiation there is no GTV to define, and only a CTV needs to be delineated

▪ An adequate absorbed dose must be delivered to the whole GTV to obtain local tumor control.

CLINICAL TARGET VOLUME

The CTV is a volume of tissue that contains a demonstrable GTV and/or subclinical malignant disease with a certain probability of occurrence considered relevant for therapy

typically a probability of occult disease higher than from 5 % to 10 % is assumed to require treatment

The delineation of the CTV is currently based on clinical experience

INTERNAL TARGET VOLUME

ITV was defined as the CTV plus a margin taking into account uncertainties in size, shape, and position of the CTV within the patient. Such a margin was called the internal margin

It was first introduced in ICRU62

PLANNING TARGET VOLUME

The PTV is a geometrical concept introduced for treatment planning and evaluation. It is the recommended tool to shape absorbed-dose distributions to ensure that the prescribed dose is actually absorbed in the CTV .

The delineation of the PTV utilizes knowledge of the presence and impact of uncertainties and variations in both the tumor location and machine parameters

PTV cont..

To ensure accurate reporting of absorbed dose to the PTV in cases for which the PTV encroaches or overlaps another PTV, OAR, or PRV, it is now recommended that the delineation of the primary PTV margins should not be compromised

in such cases subdivision of the PTV into regions with different prescribed absorbed doses (so-called PTV-sub volumes, PTVSV) may be used

The dose reporting should, however, be done for the whole PTV

Pictorial representation

ORGAN AT RISK

The OAR or critical normal structures are tissues that if irradiated could suffer significant morbidity and thus might influence the treatment planning and the absorbed-dose prescription

They may be divided into 3 classes :

Class I : Radiation lesions are fatal or result in severe morbidity.Class II : Radiation lesions result in mild to moderate morbidity.Class III : Radiation lesions are mild, transient, and reversible, or result in no significant morbidity.

PLANNING ORGAN AT RISK VOLUME (PRV)

This is a volume which gives into consideration the movement of the Organs at Risk during the treatment.

An integrated margin must be added to the Organ at Risk to compensate for the variations and uncertainties, using the same principle as PTV and is known as the Planning Organ at Risk volume ( PRV ).

A PTV and PRV may occasionally overlap.

TREATED VOLUME

It is a volume enclosed by isodose surface, selected and specified by the radiation oncologist as being appropriate to achieve the purpose of treatment .

It may closely match to the PTV or may be larger than the PTV.

If, however, it is smaller than the PTV, then the probability of tumor control is reduced and the treatment plan has to be re-evaluated or the aim of the therapy has to be reconsidered

REMAINING VOLUME AT RISK (RVR)

Ideally when delineating the OAR, especially forIMRT, all normal tissues that could potentially beirradiated should be outlined.

The imaged volume within the patient, excluding any delineated OARand the CTV(s), should be identified as the RVR

Conclusion

ICRU 83 is the recent update published on prescribing recording and reporting

The aim of this report is to standardize and harmonize all these process

It is very important to follow these recommendations to achieve the aim of radiotherapy

This report is being followed since 2010 by most of the institutions