IORT 2008

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

IORT 2008 Bataini et al, 1982

,45 55 65 75 85 95

Total dose (Gy)

0

20

40

60

80

100

120T

umor

con

trol

(%

)

Dose-response curve for neck nodes ≤ 3 cm

Tumor Control Probability (TCP)

IORT 2008

Human Monkey

Baumann et al., Strahlenther Onkol 170: 131-139, 1994

Normal Tissue Control Probability (NTCP)

IORT 2008

Target

J. John, 1974

IORT 2008 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:

IORT 2008

Target volumes in EBRT

Before Rx-CH

46 Gy (Rx-CH)

CT MRI T2 FS FDG-PET

Right piriform sinus

(ICDO-10: C12.9)

SCC grade 2

TNM 6th ed: T4N0M0

Fiberoptic examination

IORT 2008

•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

IORT 2008

Clinical Target Volume (CTV)

Target volumes in EBRT

IORT 2008

GM GMPiM PiM

UUEIV

EIAB

GM GMPiM PiM

UUEIV

EIAB

PiM PiMGM GM

EIAEIV

U U

PiM PiMGM GM

EIAEIV

U U

PiM PiMGM GM

EIAEIV

U U

GM GM

B

UU IOMIOM

GM GM

B

UU IOMIOMB

GM GM

IOM IOM

B

GM GM

IOM IOM

B

GM GM

IOM IOM

Mesorectal subsite

Lymph node regions

Posterior PS

Selection and delineation of Target Volume

Haustermans et al., 2005

IORT 2008

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

IORT 2008

PTV1: dose1

CTV1

GTV1 (pre-RxTh CT+ iv contrast)

CTV2 = GTV2

PTV2: dose2

GTV2 (FDG-PET @ 46 Gy)

ICRU IMRT report

Target volumes in EBRT

IORT 2008

Target volumes in IORT + EBRT

CTV1 = “tumor bed”

PTV1 = PTV1: dose1

IORT

PTV2: dose2

CTV2 (clinical knowledge)

EBRT

IORT 2008

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) andRemaining Volume at Risk (RVR)

ICRU IMRT report

IORT 2008

• 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 2008

IORT and Target Volumes

• GTV is typically absent

• Clinical definition of the CTV: “the operative bed”…

• PTV = CTV

• OAR = PRV are less clearly individualized

ICRU report 71, 2004

IORT 2008

The HumanCondition.

R. Magritte, 1935

IORT 2008

Absorbed dose in EBRT

• Planning aims:- PTV1: dosex, D-V constraints, …,- Spinal cord: Dmax = 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

IORT 2008

• 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 IMRTLevel of reporting

Absorbed dose in EBRT

ICRU IMRT report

IORT 2008

ICRU Reference Point Not A “Typical Point” for IMRT

Segment 1 Segment 2

Segment 3 Segment 8

Segments 4-7, 9-13

13 segment IM Field

From Jatinder Palta, University of Florida

Absorbed dose in EBRT

IORT 2008

• Dose-volume reporting:- Dv: i.e. D50 (Dmedian), D95 - Dmean

- Near minimum dose: D98

- Near maximum dose: D2

• 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 PTVAbsorbed dose in EBRT

ICRU IMRT report

IORT 2008

• “Serial-like” organs:- Dnear-max (D98).

• “Parallel-like” organs:- Dmean (e.g. parotid) ,- Vd where d refers to dose in Gy (e.g. V20 for lung).

Metrics for level 2 reporting of PRV

Absorbed dose in EBRT

ICRU IMRT report

IORT 2008

Homogeneity and Conformity

Vol

Dose

Vol

Dose

Vol

Dose

Vol

Dose

Low Homogenenity – High Conformity

High Homogeneity – Low Conformity

High Homogeneity – High Conformity

Low Homogeneity – Low Conformity

Dose Dose

DoseDose

V ol V olV olV ol

Absorbed dose in EBRT

ICRU IMRT report

IORT 2008

IORT and dose prescription, reportingand 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 Dmin and Dmax

• Recording as for EBRT

ICRU report 71, 2004

IORT 2008

• 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