Download Treatment Planning Target and Structure Definition

Treatment Planning
Target and Structure Definition
Jack Yang, Ph.D., DABR
Institute for Advanced Radiation Oncology
Barnabas Health
Long Branch, NJ 07740
New Technologies in Modern Radiotherapy, Chulabhorn
Research Institute, Bangkok, Thailand, August 22-25, 2012
Outlines
Identify the patient data acquisition
process and target (GTV) definitions
Image modalities with discussion for
target delineation
Atlas (RTOG and more)
Published papers and Netter/Gray
Anatomy books for common disease
sites
ICRU50/62 Target Volume Definition
Gross Target Volume (GTV)
visible or palpable disease
Clinical Target Volume (CTV)
GTV + subclinical extension site dependent
typically 5 to 10 mm beyond GTV
Planning Target Volume (PTV)
CTV + margin for internal organ motion
and variation in daily setup
site dependent, usually 5 to 10 mm
Beam aperture
PTV + margin for beam penumbra
(LIANC and energy dependent)
7 to 8 mm from 50% to 95%
10 -12 mm from 50% to 100%
Light
Field
margin
for
penumbra
Target and Normal Tissue Delineation
Tumor
 CTV (Clinical Target Volume)
 ITV (Internal Target Volume)
=CTV + IM (internal margins)
 PTV (Planning Target Volume)
=ITV + SM (Set up margins)
=CTV+ IM+ SM
Normal Tissue
 OAR (Organ at Risk)
 PRV (Planning organ at risk
volume)
ITV
IM
CTV
SM
PTV
OAR
PRV
Target and Normal Tissue Delineation
•
Internal Margin (IM)
Margin accounts for
variations in size
shape and position
of CTV in relation to
anatomy
Setup Margin (SM)
Accounts for
uncertainties in
patient-beam
positioning
Planning Organ at Risk
Volume (PRV)
Similar to PTV
Volume accounting
for margin about
critical structures
near or inside
irradiated volume
–
•
–
•
–
–
Class C
Global safety margins
Smaller margins
Based on clinical
experiences of toxicity,
or proximity of organs
at risk
Class B
Reduce PTV
Non-linear addition of
IM + SM
Class A
Linear addition of IM +
SM
Internal margin
accounts for variations
in position or shape of
CTV
Setup margin accounts
for variations in
positioning
PTV/PRV Margins (ICRU 62)
PTV (Planning Target volume)
PRV (Planning Organs at Risk (OAR) Volume)
PTV (PRV)= CTV (OAR) + Margins
Uncertainty sources
Internal Margins (IM): size, shape and position of the CTV in
relation to anatomical reference points
Setup Margins (SM):
To account specifically for uncertainties (inaccuracies and lack of
reproducibility) in patient positioning and alignment of the
therapeutic beams during treatment planning and through all
treatment sessions.
Target and Normal Tissue Delineation
SBRT
SBRT:
–
–
–
–
•
Gating
Body fixation
IGRT
4D scan estimation of
tumor trajectories
Can thus reduce SM,
IM, and even some CTV
by selecting a portion
of phase of tumor
motion.
2D/3D
Target and Normal Tissue Delineation
Target and normal structure delineation
requirements for conformal
radiotherapy have been addressed by
the ICRU.
Often most time consuming portion of
the virtual simulation process and care
should be taken to simplify this task as
much as possible.
Well designed contouring software
package is a prerequisite and should be
one of main concerns when selecting
virtual simulation software.
GTV/CTV
Unfortunately, in many sites anatomic imaging techniques
(i.e., CT or MRI) do not always distinguish malignant from
normal tissues.
PET or PET/CT
has been
utilized to
routinely
delineate
GTV/CTV w/
proper margin
tools
PTV – Defining Margin
Reviewing article by Langen and Jones, IJROBP 50, 265278, 2001
Defining PTV
When CTV/GTV changes shape dramatically from one CT slice to
next, larger PTV margin must be used in slice containing smaller
CTV/GTV to obtain PTV coverage in the inferior-superior
direction.
Proper PTV margin
PTV – Positional Uncertainties
Physician should account for the asymmetrical nature of
positional uncertainties.
No. of
Patients
Comments
Displacement
(mm)
Max.
(mm)
10
Radio-opaque marker
full bladder
weekly portals, relative
to a reference portal
image
AP: 4.5
AP: 7.5
Lat: 1.7
Lat: 2.0
SI: 3.7
SI: 5.0
Balter, JM, Lam, K, Sandler, HM, Littles, JF, Bree, RL, Ten Haken, RK:
Measurement of prostate movement over the course of routine radiotherapy
using implanted markers. Int. J. Radiat. Oncol. Biol. Phys. 31:113-118, 1995
4D CT – Application in Simulation
An imaging technique for providing a set of CT images
for a specific breathing phase.
A multi-slice CT scanner is used and the couch speed is
reduced to accommodate breathing cycle
During the scanning the patient’s breathing phase is
monitored using a device such as Philips Bellows,
Varian’s Real-time Position Management System (RPM)
or Elekta’s Active Breathing Coordinator (ABC).
The data acquired data is then sorted by breathing
phase (binning), and phase specific images can be
reconstructed.
4D CT – Image Cycle
•
•
•
•
Tool
Principle
Advantages
Limitations
4D CT – a Lung Case
mid exhale
mid inhale
end exhale
end inhale
4D CT - Process for Sorting/Binning
GTV – 4D CT
Std light breathing scan
0% Phase of 4D scan
Courtesy G. Chen, Ph.D./MGH
SBRT Contouring Tips
Because of the tight field margins used, errors in
GTV delineation is much less forgiving than
conventional treatment.
Some variables to consider





CT slice thickness (both diagnostic and planning)
and field of view
Axial vs. helical imaging
Patient breathing/breath hold, 4DCT
Diagnostic modality that best represents the tumor
CT vs.MR vs. PET
For each of the modalities windowing/leveling plays
a key role
Contouring of Lung Lesions
Use the appropriate windowing/leveling for the anatomy being contoured.
(Mediastinal window/level is not appropriate for identifying this lung lesion.)
Contour the entire cross-section of the structure, e.g. esophagus includes the
mucosa, submucosa & all muscular layers out to the fatty adventitia. (RTOG
0813)
Subtract the GTV from the organ being treated.
Optical Chiasm
Brain Stem
Landmarks – Sella, CSF
Landmarks – Clivus, C1
Spinal Cord
Landmarks – C1, Vertebrae body, end at
L1-L2
5 mm cord margin
Parotid
Landmarks – mandible, styoid, and
masseter, can visualize well by changing
window/level
Breast
Breast
Heart
Lumpectomy
Tips for Contouring Male OARs
This is the slice which defines the
last slice of rectum, the following
slice will connect anteriorly with the
rectosigmoid.
Still counted as the femoral head
RTOG 1106 - Thoracic
Lung
Spinal cord should also start at this level just below the cricord or
from the base of skull C1 if scan is available, particularly when
the tumors involve neck or apex.
RTOG 1106 - Thoracic
RTOG 1106 – Locating Brachial Plexus
Timmerman’s Trick-1
clavicle
Vein, artery, and nerve (VAN,
anterior to posterior) will go over
the 1st rib and under the clavicle
Using coronal images, find the
plane where vascular/nerve
structures (tubes and wires) pass
between the 1st rib and clavicle
1st rib
Roughly contour these neurovascular tissues in this coronal
plane (as shown in yellow)
You will use these rough
contours in the next step
Courtesy of RTOG 1106 protocol
RTOG Hippocampus Contouring
Red: Hippocampus
Green: Hippocampal Avoidance Zone
Hippocampal 1)
Hippocampal
1)
Tail
Tail
2) Body
Body
3)2)
Head
3) Head
The hippocampus has three anatomic subdivisions: the head, body, and tail; note that the head is
inferior or caudad, the body is superoposterior and the tail is most cephalad (superior) and
posterior, and an overall “banana” shape emerges on sagittal images, located in the plane of the
lateral ventricle.
MR Images courtesy of: Holmes CJ, Hoge R, Collins L, et al. "Enhancement of
MR Images Using Registration for Signal Averaging" Journal of Computer
Assisted Tomography 22, 324-333 (1998)
29
RTOG Sarcoma Working Group
RTOG Sarcoma Radiation Oncologists Reach Consensus on Gross
Tumor Volume (GTV) and Clinical Target Volume (CTV) on Computed
Tomographic Images for Preoperative Radiotherapy of Primary Soft
Tissue Sarcoma of Extremity in RTOG Studies. IJROBP June 2011
Conclusion
Imaging modalities (CT/MR/PET/NM) are basics
for target and OAR delineation.
CT (4D CT) Simulation has gradually replaced the
current simulation process and can improve the
quality for target definition if properly operated.
Clinical volume margins vary from clinic to clinic,
standards such as RTOG can be the starting
references.
Target and critical structures are the most
important ingredients for quality treatments,
anatomy knowledge from physicians is critical.