Iort

Precision in Radiation Oncology: what are the standards and how could it apply to IORT Vincent GREGOIRE, MD, PhD, hon. FRCP Radiation Oncology Dept., & Center for Molecular Imaging and Experimental Radiotherapy, Université Catholique de Louvain, St-Luc University Hospital, Brussels, Belgium

Bataini et al, 1982 , 4 5 5 5 6 5 7 5 8 5 9 5 T o t a l d o s e ( G y ) 0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 Tumor control (%) Dose-response curve for neck nodes ≤ 3 cm Tumor Control Probability (TCP)

 Human  Monkey Baumann et al., Strahlenther Onkol 170: 131-139, 1994 Normal Tissue Control Probability (NTCP)

Target J. John, 1974

ICRU report 62, 1999
Gross Tumor Volume: GTV
Clinical Target Volume: CTV
Internal Target Volume: ITV
Planning Target Volume: PTV
Organ at Risk: OAR
Planning Organ at Risk Volume: PRV
Target volumes in Radiation Oncology: ICRU 50 and 62:

Target volumes in EBRT Before Rx-CH 46 Gy (Rx-CH) Right piriform sinus (ICDO-10: C12.9) SCC grade 2 TNM 6 th ed: T4N0M0 Fiberoptic examination CT MRI T2 FS FDG-PET

The Clinical Target Volume (CTV) is a volume of tissue that contains a demonstrable GTV and/or subclinical malignant disease at a certain probability considered relevant for therapy…,
The CTV is thus an anatomical-clinical concept.
Clinical Target Volume (CTV) ICRU IMRT report Target volumes in EBRT

Clinical Target Volume (CTV) Target volumes in EBRT

Mesorectal subsite Lymph node regions Posterior PS Selection and delineation of Target Volume Haustermans et al., 2005

The Planning Target Volume is a geometrical concept, introduced for treatment planning and evaluation. It is the recommended tool to shape dose distributions that ensure with a clinically acceptable probability that an adequate dose will actually be delivered to all parts of the CTV… Planning Target Volume (PTV) ICRU IMRT report Target volumes in EBRT

CTV 2 = GTV 2 ICRU IMRT report Target volumes in EBRT PTV 1 : dose 1 CTV 1 GTV 1 (pre-RxTh CT+ iv contrast) PTV 2 : dose 2 GTV 2 (FDG-PET @ 46 Gy)

Target volumes in IORT + EBRT CTV 1 = “tumor bed” PTV 1 = PTV 1 : dose 1 IORT PTV 2 : dose 2 CTV 2 (clinical knowledge) EBRT

Normal tissues in EBRT
Distinction between “serial-like” (e.g. spinal cord) and “parallel-like organs” (e.g. parotid gland),
For “tubed” organs (e.g. rectum) wall delineation,
Remaining Volume at Risk (RVR): optimization and late effects (e.g. carcinogenesis).
Organ At Risk (OAR) and Remaining Volume at Risk (RVR) ICRU IMRT report

PRV is a geometrical concept (tool) introduced to ensure that adequate sparing of OAR will actually be achieved with a reasonable probability ,
A positive OAR to PRV margin for serial organ.
Dose-volume constraints on OAR are with respect to the PRV,
Priority rules when overlapping PTVs or PTV-PRV(OAR),
Dose is reported to the PRV.
Planning Organ at Risk Volume (PRV) ICRU IMRT report Normal tissues in EBRT

IORT and Target Volumes
GTV is typically absent
Clinical definition of the CTV: “the operative bed”…
PTV = CTV
OAR = PRV are less clearly individualized

The Human Condition. R. Magritte, 1935

Absorbed dose in EBRT
Planning aims:
PTV 1 : dose x , D-V constraints, …,
Spinal cord: D max = x Gy, …,
…
Prescription:
Physician’s responsibility,
Acceptance of doses, fraction #, OTT, D-V constraints, beam number, beam orientation, …
Treatment delivery:
Instruction file sent to the linac and/or RVS.
Dose prescription in 3D-CRT and IMRT ICRU IMRT report

Level 1: not adequate for 3D-CRT – IMRT,
Level 2: standard level for dose reporting,
Level 3: homogeneity, conformity and biological metrics (TCP, NTCP, EUD, …) and confidence intervals.
Dose recording in 3D-CRT and IMRT Level of reporting Absorbed dose in EBRT ICRU IMRT report

ICRU Reference Point Not A “Typical Point” for IMRT Segments 4-7, 9-13 13 segment IM Field From Jatinder Palta, University of Florida Absorbed dose in EBRT Segment 1 Segment 2 Segment 3 Segment 8

Dose-volume reporting:
D v : i.e. D 50 (D median ), D 95
D mean
Near minimum dose: D 98
Near maximum dose: D 2
State the make, model and version number of the treatment planning and delivery software used to produce the plans and deliver the treatment.
Metrics for level 2 reporting of PTV Absorbed dose in EBRT ICRU IMRT report

“ Serial-like” organs:
D near-max (D 98 ).
“ Parallel-like” organs:
D mean (e.g. parotid) ,
V d where d refers to dose in Gy (e.g. V 20 for lung).
Metrics for level 2 reporting of PRV Absorbed dose in EBRT ICRU IMRT report

Homogeneity and Conformity Low Homogenenity – High Conformity High Homogeneity – Low Conformity Dose Dose Dose Dose Vol Vol Vol Vol Absorbed dose in EBRT ICRU IMRT report Vol Dose Vol Dose Vol Dose Vol Dose High Homogeneity – High Conformity Low Homogeneity – Low Conformity

IORT and dose prescription, reporting and recording
Level 1 (2-D) dose prescription, reporting and recording…
Dose prescription at 90% isodose for electron beams
Reporting of ICRU reference point dose, and best estimate of D min and D max
Recording as for EBRT

Recommendations for common understanding and proper prescription and reporting especially in combined treatment, e.g. IORT followed by EBRT
Less sophisticated prescription and reporting for IORT
Volumetric prescription and reporting…?
Conclusions

Conclusions
ICRU recommendations still needed even for 3D-CRT and IMRT to avoid unwanted treatment heterogeneity,
New report based on ICRU foundations, e.g. volumes,
Adjustments and modifications performed when necessary, e.g. dose-volume reporting,
Final draft ready for early 2007 / publication in early 2008
ICRU report on 3D-CRT and IMRT

Recording in 3D-CRT and IMRT
Electronic archiving for at least the life of patient or 5 years – whatever is longer,
Complete reconstruction of the treatment plan and delivery record,
For clinical trials, longer archiving if scientifically justified.
Absorbed dose in EBRT ICRU IMRT report

Sometimes the largest component of the margin between the GTV and CTV will be the delineation error in drawing the GTV,
Consideration should be made for this in the clinical margin.
Clinical Target Volume (CTV) Target volumes in Radiation Oncology

Planning Target Volume (PTV) Target volumes in Radiation Oncology
Include both “internal” and “external” variations of the CTV,
Separate delineation of the ITV may not be necessary,
Expansion of the CTV using “rolling ball” algorithms,
CTV to PTV margin recipe based on random and systematic errors,
Priority rules when overlapping PTVs or PTV-PRV,
Dose is prescribed and reported on the PTV.

CTV to PTV margin recipe Target volumes in Radiation Oncology Van Herk, 2003

Effect Dose Uncomplicated tumor control: Therapeutic Ratio Unacceptable normal tissue damage Tumour control Uncomplicated tumour control

ICRU committee on volume and dose specification for prescribing, reporting and recording special techniques in external photon beam therapy: conformal and IMRT. Vincent GREGOIRE, M.D., Ph.D. and Thomas R. MACKIE, Ph.D.* Radiation Oncology Dept., & Center for Molecular Imaging and Experimental Radiotherapy, Université Catholique de Louvain, St-Luc University Hospital, Brussels, Belgium and * Dept. of Medical Physics, University of Wisconsin, Madison, WI, USA.

The stone of Rosette (Champolion)

The need for an new ICRU report on 3D-CRT and IMRT
Biological Target Volume (BTV): C. Ling, IJROBP 2000,
Hypoxic TV (HTV), Proliferation TV (PTV), …: ESTRO physics meeting, 2003,
working PTV (wPTV): Ciernik IF, IJROBP, 2005,
AAPM 2005: “… with the use of IMRT, ICRU recommendations will not be needed anymore…”.
It was published and/or mentioned …

ICRU committee for 3D-CRT and IMRT
Sponsors
Andr é Wambersie MD, PhD, Brussels, Belgium
Paul DeLuca PhD, Madison, USA
Reinhard Gahbauer MD, Ph.D, Columbus, USA
Gordon Whitmore Ph.D, Toronto, Canada
Chairmen
Vincent Grégoire MD PhD, Brussels, Belgium
T. Rock Mackie PhD, Madison, USA
Members
Wilfried De Neve MD PhD, Gent, Belgium
Mary Gospodarowicz MD, Toronto, Canada
Andrzej Niemierko PhD, Boston, USA
James A. Purdy PhD, Sacramento, USA
Marcel van Herk PhD, Amsterdam, The Netherlands
Consultants
Anders Ahnesjö PhD, Uppsala, Sweden
Michael Goiten PhD, Windisch, Switzerland
Nilendu Gupta PhD, Colombus, USA

ICRU report 62, 1999 Target volumes in Radiation Oncology Unresolved issues for 3D-CRT and IMRT
Multiple GTV, e.g. anatomic vs functional imaging; before and during treatment, …,
GTV to CTV margins: clinical probability,
CTV to PTV margins: geometric probability; overlapping volumes,
ITV ???
OAR: open vs closed volume? Remaining normal tissues?
PRV: serial vs parallel OAR.

Organ At Risk (OAR) PTV Rectal wall Rectum ICRU IMRT report Normal tissues in EBRT

Parotid sparing with IMRT ICRU IMRT report Normal tissues in EBRT Superficial lobe Superficial and deep lobe

“ Cheating on the PTV margins”
The practice of shrinking the CTV to PTV margin to accommodate an OAR is discouraged as it results in a deceptively better PTV homogeneity,
In IMRT the trade-off can be accomplished by changing the planning aims in the optimizer,
In 3-D CRT, the trade-off can be accomplished with a separate target delineation used to draw the beam boundary.
ICRU IMRT report Target volumes in EBRT

ICRU report 62, 1999 Absorbed dose in Radiation Oncology: ICRU 50 and 62:
Dose prescription:
Responsibility of the treating physician.
Dose reporting:
ICRU reference point,
Three-levels of dose reporting,
Point-doses: D ICRU point , D min , D max , …
Dose recording.

ICRU report 62, 1999 Absorbed dose in Radiation Oncology: Unresolved issues for 3D-CRT and IMRT
Discrepancy between dose-volume constraint prescription and dose delivery,
Single point dose prescription,
Single point dose reporting,
Biological metrics (e.g. EUD, TCP, NTCP, …),
Uncertainties in dose reporting,
Quality assurance.

Dose-Volume Reporting D 95 D 2 0 10 20 30 40 50 60 70 80 90 100 50 55 60 65 70 Dose (Gy) Percent Volume D98=60Gy D50=60Gy D v with v≠50 may require a change in prescription value D 98 D 50 is close to ICRU Reference Dose at a Point Absorbed dose in EBRT

Homogeneity:
- Standard deviation in dose to the PTV.
Conformity:
- Conformity Index: CI = TV/PTV,
Dice Similarity Coefficient (DSC):
DSC = TV  PTV / TV  PTV 
Examples of metrics for level 3 reporting of PTV Absorbed dose in EBRT

QA in 3D-CRT and IMRT
Appropriate QA of TPS and equipments,
Patient QA not limited to single-point dose check,
Phantom QA using measured dose and not limited to a single measurement point.
Independent dose calculation algorithms with similar or better dose calculation accuracy.

QA in 3D-CRT and IMRT
Previous ICRU 5% point-dose accuracy specification replaced by a volumetric dose accuracy specification.
Proposed new ICRU volumetric dose accuracy specification:
High gradient (≥ 20%/cm): 85% of points within 5mm,
Low gradient (< 20%/cm): 85% of points within 5% of predicted dose normalized to the prescribed dose.

ICRU committee for 3D-CRT and IMRT ICRU IMRT report GTV 1 CTV 1 PTV 1 CTV 2 PTV 2 CTV 3 PTV 3 Microscopic Extension Regional Involvement

Example 1 ICRU IMRT report Target volumes in EBRT PTV 1 : dose 1 CTV 1 PTV 2 : dose 2 GTV 1 (pre-RxTh CT+ iv contrast) CTV 2 = GTV 1

Dose-Volume Reporting D 50 best corresponds to the level at D ICRU-point Absorbed dose in EBRT 0 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 25 30 35 40 45 50 55 60 65 Dose (Gy) Percent Volume Differential Cumulative D 95 D 98 D 50 D 2 D 50 = 60 Gy

http://www.slideshare.net	18
http://radiotherapyhome-fondas.blogspot.com	9
http://translate.googleusercontent.com	1

Iort

by fondas vak on Mar 27, 2010

Accessibility

Categories

Tags

Upload Details

Usage Rights

3 Embeds 28

Statistics

Iort — Presentation Transcript