La prescrizione della dose nei trattamenti stereo-RT e radiochirurgici: dall’ICRU a ROSEL ed altro

La prescrizione della doseLa prescrizione della dose
nei trattamentinei trattamenti
stereo-RT e radiochirurgici:stereo-RT e radiochirurgici:
dall’ICRU a ROSEL ed altrodall’ICRU a ROSEL ed altro
Giovedì 21 Novembre 2013 – Deodato, Cilla, De Filippo, Masiello

When delivering a radiotherapy treatment,
parameters such as volume and dose have to be
specified for different purposes:
prescription, recording, and reporting. It is
important that clear, well defined and
unambigous concepts and parameters are used
for reporting purposes to ensure a common
language between different centers.
When delivering a radiotherapy treatment,
parameters such as volume and dose have to be
specified for different purposes:
prescription, recording, and reporting. It is
important that clear, well defined and
unambigous concepts and parameters are used
for reporting purposes to ensure a common
language between different centers.

ICRU
International commision on Radiation Units, Prescribing, Recording and Reporting Photon Beam Therapy, ICRU REPORT 50, 1993
The International Commission on Radiation Units and
Measurements (ICRU), since its inception in 1925, has had as its
principal objective the development of internationally acceptable
recommendations regarding:
• Quantities and units of radiation and radioactivity
• Procedures suitable for the measurement and application of
these quantities in clinical radiobiology
• Physical data needed in the application of these procedures, the
use of which tends to assure uniformity in reporting

Target volumes – ICRU 50 e 62
ICRU 50 (1993): 1993 to 1999
ICRU 62 (1999): 1999 to till date

ICRU Reports – ICRU 50
Volumes defined prior to treatment planning :
- Gross Tumor Volume (GTV)
- Clinical Target Volume (CTV)
Volumes defined during the treatment planning :
- Planning target Volume (PTV)
- Organs at risk
- Treated Volume
- Irradiated Volume

GROSS TUMOR VOLUME ( GTV )
• Gross palpable or visible/demonstrable extent and location of the
malignant growth
• It consists of :
- Primary tumor
- Metastatic lymphadenopathy
- Other metastasis
• Corresponds to those parts of the malignant growth where the
tumor density is largest.
• If the tumor has been removed prior to radiotherapy then no GTV
can be defined.

GROSS TUMOR VOLUME ( GTV )

CLINICAL TARGET VOLUME ( CTV )
• It is a tissue volume that contains a GTV and/or subclinical
microscopic disease, which has to be eliminated
• This volume has to be treated adequately in order to achieve
the aim of therapy : cure or palliation
• The delineation of this volume requires consideration of
factors like local invasive capacity of the tumor and its
potential to spread to different regions ( eg: regional lymph
nodes).

CLINICAL TARGET VOLUME ( CTV )

PLANNING TARGET VOLUME ( PTV )
• It is a geometrical concept, and is defined to select
appropriate beam sizes and arrangements, taking into
consideration the net effect of all possible geometrical
variations, in order to ensure that the prescribed dose is
actually absorbed in the CTV.
• It is used for dose planning and for specification of dose.
• It has to be clearly indicated on sections used for dose
planning and the dose distribution to the PTV has to be
considered to be representative of the dose to the CTV.

PLANNING TARGET VOLUME ( PTV )

TREATED VOLUME - 1
• It is a volume enclosed by an isodose surface, selected and
specified by the radiation oncologist as being appropriate to
achieve the purpose of treatment ( tumor eradication or
palliation ).
• It may closely match to the PTV or may be larger than the PTV.
• If, however, it is smaller than the PTV, or not wholly enclosing
the PTV, then the probability of tumor control is reduced and
the treatment plan has to be revaluated or the aim of the
therapy has to be reconsidered.

TREATED VOLUME - 2
Reasons for identification of Treated Volume are :
1.The shape and size of the Treated Volume relative to the PTV is
an important optimization parameter.
2.Also, a recurrence within a Treated Volume but outside the
PTV may be considered to be a “true”, “in-field” recurrence due
to inadequate dose and not a “marginal” recurrence due to
inadequate volume.

ORGANS AT RISK ( OR )
• These are normal tissues whose radiation sensitivity may significantly
influence the treatment planning and/or prescribed dose.
• They may be divided into 3 classes :
1. Class I : Radiation lesions are fatal or result in severe morbidity.
2. Class II : Radiation lesions result in mild to moderate morbidity.
3. Class III : Radiation lesions are mild, transient, and reversible,
or result in no significant morbidity.

IRRADIATED VOLUME ( IRV )
• It is that tissue volume which receives a dose that
is considered significant in relation to normal tissue
tolerance.
• It depends on the treatment technique used.

ICRU 50 - Summary
Irradiated Volume
Treated Volume
Planning Target Volume
(PTV)
Clinical Target Volume
(CTV)
Gross Tumor Volume
(GTV)

ICRU REPORT 62 ( Supplement to ICRU REPORT 50 )
International commision on Radiation Units, Prescribing, Recording and Reporting Photon Beam Therapy (Supplement tp ICRU Report 50), ICRU
REPORT 62, Issued 1 November 1999
• Gives more detailed recommendations on the different
margins that must be considered to account for anatomical
and geometrical variations and uncertainties
• Introduces a Conformity Index (CI)
• Gives information about how to classify Organs at Risk
• Introduces a Planning Organ at Risk Volume (PRV)
• Gives recommendations on graphics

ICRU REPORT 62
Volumes defined prior to treatment planning :
- Gross Tumor Volume (GTV)
- Clinical Target Volume (CTV)
Volumes defined during the treatment planning :
- Planning target Volume (PTV)
- Treated Volume → must be enclosed in the 95% isodose
- Irradiated Volume → must be enclosed in the 50% isodose
- Planning Organ at Risk Volume (PRV)
Same as
ICRU 50

INTERNAL MARGIN (IM) AND INTERNAL TARGET VOLUME (ITV)
• It is the margin given around the CTV to compensate for all
variations in the site, size and shapes of organs and tissues
contained in/or adjacent to CTV
• These may result from respiration, different fillings of the
bladder and rectum, swallowing, heart beat, movements of
bowel etc.
• These are physiological variations which are very difficult to
control and result in changes in the site, size and shape of
CTV.

SET-UP MARGIN (SM)
• There can be many uncertainties (inaccuracies and lack of
reproducibility) in patient positioning and alignment of the
therapeutic beams during treatment, planning and through all
treatment sessions.
• These uncertainties depend on factors like :
• variations in pt. positioning
• mechanical uncertainties of the equipment (sagging of
gantry, collimators, and couch)
• dosimetric uncertainties
• transfer set-up errors from CT & simulator to the
treatment unit
• human factors
SET-UP MARGIN (SM) is the margin that must
be added to account specifically for
uncertainties (inaccuracies and lack of
reproducibility) in patient positioning and
aligment of the therapeutic beams during
treatment planning and through all treatment
sessions.

CONFORMITY INDEX (CI)
• It is defined as the quotient of the Treated Volume and the
volume of 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.
CI = TV/PTV

ORGANS AT RISK
• According to the functional models based on the FSU (Functional Sub
Unit) concept [ Withers et al., Kallman et al., and Olsen et al. ] for the
purpose of evaluation of the volume-fractionation-response, the tissues
of an Organ at Risk are considered to be functionally either “serial”
“parallel” or “serial-parallel” structures.
Spinal cord Lung Heart

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

ICRU 62
GTVCTVITVPTVORPRV TVIrradiated volume

ADSORBED DOSE DISTRIBUTION
•The dose given to the tumor should be as homogenous as possible.
• In cases of heterogeneity of doses, the outcome of the treatment
cannot be related to the dose. Also, the comparison between different
patient series becomes difficult.
• However, even if a perfectly homogenous dose distribution is
desirable, some heterogeneity is accepted due to technical reasons.
•The heterogeneity should be foreseen while prescribing a treatment,
and, in the best technical and clinical conditions should be kept within
+7% and -5% of prescribed dose (Wittkamper et al., Brahme et al.,
Mijnheer et al.)

MAXIMUM DOSE ( Dmax )
• It is the maximum dose to the PTV and the Organ at Risk
• The maximum dose to normal tissue is important for limiting
and for evaluating the side-effects of treatment
• Dose is reported as maximum only when a volume of tissue of
diameter more than 15mm is involved (smaller volumes are
considered for smaller organs like eye, optic nerve, larynx)
• When the maximum dose outside PTV exceeds the prescribed
dose, then a “Hot Spot” can be identified

HOT SPOTS
• It represents a volume outside the PTV which receives a dose
larger than 100% of the specified dose
• A Hot Spot is considered significant only if the minimum
diameter exceeds 15mm (in smaller organs like eye, optical
nerve, larynx etc. a diameter smaller than 15mm is also
considered significant).

MINIMUM DOSE ( Dmin )
• It is the smallest dose in a defined volume.
• In contrast to maximum adsorbed dose, no volume limit is
recommended when reporting minimum dose.

ICRU REFERENCE POINT
It has to be selected according to the following general criteria :
- the dose at the point should be clinically relevant
- the point should be easy to define in a clear and
unambiguous way
- the point should be selected so that the dose should be
accurately determined
- the point should be in a region where there is no steep
dose gradient

ICRU REFERENCE POINT -2
The recommendations will be fulfilled if the ICRU reference point
is located :
• always at the centre ( or in the central part ) of PTV, and
• when possible, at the intersection of the beam axes.

ICRU REFERENCE DOSE
It is the dose at the ICRU Reference Point and
should always be reported.
• Since the CTV can move in space and can change size and shape, the
dose at the center, the maximum and the minimum dose, and the dose-
volume histograms cannot be determined with high accurancy
• As far as the dose at the center of the CTV is concerned, its value is
generally close to that of the dose at the center of the PTV, which thus can
be reported as a reasonable estimate of the dose at the center of the CTV

REPORTING
• It should be done in order to make exchange of information between
different centers.
• It is important that the treatments performed in various centers be reported
in the same way, using the same concepts and definitions.
• According to the recommendations of ICRU, as a basic requirement, the
following doses should always be reported :
 the dose at ICRU reference point
 the maximum dose to the PTV
 the minimum dose to the PTV

Physics of Radiosurgery
• Stereotactic radiosurgery (SRS) involves the use of numerous beamlets of radiation
aimed precisely at an immobilized target to deliver a single session of high dose
radiation
• The term “stereotactic” implies the targeting, planning, and directing of therapy
using beams of radiation along any trajectory in 3-D space toward a target of known
3-D coordinates
• The main dose is deposited at the intersection of these beamlets with a steep dose
fall-off outside the target
• Radiosurgery becomes prohibitive at size in excess of 4 to 5 cm
• The mainly used sources are:
 Cobalt-60 (Gamma-Knife and the Rotating Gamma System)
 X-Rays (Linear Accelerator)
 Protons

Radiobiology
• The use of single fraction to treat a small volume
differs significantly from conventional EBRT
• There is a increased biologic effect on normal tissues
more pronounced than it is on tumors
FRT SBRT
EXPLOIT TEMPORAL EFFECTS OF CELL
CYCLE DISTRIBUTION
NO
TAKE ADVANTAGE OF THE
REOXYGENATION OF THE TUMOR
NO
REPOPULATION MINIMIZES THE EFFECT OF
REPOPULATION
LESS ENDOTHELIAL APOPTOSIS ENDOTHELIAL APOPTOSIS

Historical Landmarks in Radiosurgery - 1
YEAR AUTHOR LOCATION EVENT
1951 Leksell Stokcholm Invention of “Stereotactic
Radiosurgery” using
rotating orthovoltage unit
1952 Lawrence Berkeley Use of heavy particle
treatment for pituitary for
cancer pain
1964 Kiellberg Boston Use of protobeam for
inntracranial radiosurgery
1967 Leksell Stockholm Invention of Gammaknife
using cobalt-60 sources
1970 Steiner Stockholm Use of Gammaknife for
AVM’s
1980 Fabrikant Berkley Use of Helium ions for
AVM’s

The Past of Radiosurgery
Orthovoltage Xrays tube Particle beam
Lars Leksell - 1951
• Coined the term “radiosurgery”
• First procedures done with orthovoltage Xrays tube
• After initially experimenting with particle beam, designed
Gammaknife with 179 cobalt-60 sources in a Hemisphere array
Acta Chirur Scand, The stereotaxic method and radiosurgery of the brain. 1951 Dec13;102(4):316-9

Historical Landmarks in Radiosurgery - 2
YEAR AUTHOR LOCATION EVENT
1982 Betti,
Colombo
Buenos Aires
Vicenza
Independent development of a
system adapting LINAC’s for
radiosurgery
1986 Lutz/Winston JCRT Development of LINAC based SRS
based on common stereotactic frame
1987 Lundsford Pittsburgh First Gammaknife installed in
the US
1991 Friedman/Bova Florida Development of a more reliable
technique for highly conformal
radiosurgery
1991 Lax
Blomgren
Karolinska First to propose extending SRS
outside of the skull
1992 Loeffler/Alexander Boston First commercially Built dedicated
SRS LINAC (Varian-SRS)
1993 Laing Boston Gill-Thomas-Cosman
relocatable frame

Dose and prescription in SRS with linear accelerator
• The average “treatment” distance error for a target was found to be
1.33+/- 0.64 mm where 0.64 mm is the standard deviation for a single
treatment
• Prescribing dose to the 80% surface (target center being 100%)
Lutz W, Winston KR e al A system for stereotactic radiosurgery with a linear accelerator, Int J Radiation Oncol Biol Phys Vol 14 pp 373-381

ASTRO /ACR guidelines for the performance of SRS
Seung SK, Larson DA e al. American College of Radiology (ACR) and American Society for Radiation Oncology (ASTRO) Practice Guideline for the

SBRT Dose prescription (lung)
Nagata Y, Matsuo Y, Takayama K, NorihisaY, Mizowaaki T, MitsumoriM, Shibuya K, Yano S, Narita Y, Hiraoka M. Current status of stereotactic
body radiotherapy for lung cancer. Int J Clin Oncol 2007

SBRT Dose prescription (lung)
Wulf J, Bajer K, Mueller G, Flentje MP. Dose-response in stereotactic irradiation of lung tumors. Radiotherapy and Oncology 2005

SBRT Dose prescription (liver)
Wulf J, Guckemberg M, Haedinger U, Oppitz U. Mueller G, Baier K & Flentje M. Stereotactic radiotherapy of primary liver cancer and hepatic
metastases. Acta Oncologica 2006

SBRT Dose prescription (brain)
Ohtakara K, Hayashi S, Tanaka Hoshi H. Consideration of optimal isodose surface selection for target coverage in micro-multileaf collimator-
based stereotactic radiotherapy for large cystic brain metastases: comparison of 90, 80 and 70% isodose surface-based planning. The Brithish
Journal of Radiology 2012

• Users have a wide choice of prescription modalities
• Resulting dose distribution is influenced by treatment delivery platform, target
geometry, treatment site, …..
• The nature of dose falloff into normal tissue (gradient dose) remain less
optimized
• This gradient is influenced by:
number of beams, beam shape, beam direction and …..
beam aperture dimension (block margin)
choice of target prescription isodose
Introduction to ROSEL study

Hurkmans e al, Recommendations for implementing stereotactic radiotherapy in peripheral stage IA non-small cell lung cancer: report from
the Quality Assurance Working Party of the randomised phase III ROSEL study, Radiation Oncology, January 2009, 4:1
BLOCK MARGIN: the fundamental picture (1)

Hong e al: LINAC-based SRS: Inhomogeneity, conformity and dose fall off, Med Phys., Vol 38, No. 3, March 2011
BLOCK MARGIN: the fundamental picture (2)

Hurkmans e al, Recommendations for implementing stereotactic radiotherapy in peripheral stage IA non-small cell lung cancer: report from the Quality
Assurance Working Party of the randomised phase III ROSEL study, Radiation Oncology, January 2009, 4:1
Herfarth KK, Stereotactic irradiation of liver metastases, Radiologe 2001 Jan; 41(1): 64-8

A simulated dose prescription on liver: UCSC Roma/Campobasso

LIVER
0
20
40
60
80
100
0 20 40 60 80 100 120 140
Volume
Dose
Margin 5 mm
Margin 2.5 mm
Margin 0 mm
PTV
0
20
40
60
80
100
0 20 40 60 80 100 120 140
Volume
Dose
Margin 5 mm
Margin 2.5 mm
Margin 0 mm
GTV
0
20
40
60
80
100
0 20 40 60 80 100 120 140
Volume
Dose
Margin 5 mm
Margin 2.5 mm
Margin 0 mm
V7Gy<50%
V12Gy<30%
A simulated dose prescription on liver: UCSC Roma/Campobasso

La prescrizione della dose nei trattamenti stereo-RT e radiochirurgici: dall’ICRU a ROSEL ed altro

Recomendados

Recomendados

Mais conteúdo relacionado

Mais procurados

Mais procurados (20)

Destaque

Destaque (20)

Semelhante a La prescrizione della dose nei trattamenti stereo-RT e radiochirurgici: dall’ICRU a ROSEL ed altro

Semelhante a La prescrizione della dose nei trattamenti stereo-RT e radiochirurgici: dall’ICRU a ROSEL ed altro (20)

Último

Último (20)

La prescrizione della dose nei trattamenti stereo-RT e radiochirurgici: dall’ICRU a ROSEL ed altro