Transcript Document

HST.187: Physics of Radiation Oncology
#5. Intensity-modulated radiation
therapy: IMRT and IMPT
Part 2: IMPT
Joao Seco, PhD
[email protected]
Alexei Trofimov, PhD
[email protected]
Dept of Radiation Oncology MGH
March 6, 2007
IMRT is a treatment technique with multiple fields, where
each field is designed to deliver a non-uniform dose
distribution.The desired (uniform) dose distribution in the
target volume is obtained after delivery of all treatment fields.
Flexible field
definition,
sharper dose
gradients
Higher dose
conformity
IMRT Coll. Work Group
IJROBP 51:880 (2001)
Improved
sparing of
healthy tissue
Protons vs. Photons
Ideal
Intensity Modulated Proton Therapy
IMPT = IMRT with protons
Intensity Modulated Proton Therapy
• Planning approaches
• Delivery options (inc. MGH plan)
• Overview of IMPT treatments / development
• Special considerations for IMPT
• IMPT vs. 3D-conformal proton vs. photon IMRT
in the clinic
Proton depth-dose distribution: Bragg peak
Depth = additional degree of freedom with protons
H.Kooy
BPTC
A. Lomax: “Intensity modulation methods for proton RT”
Phys. Med. Biol. 44:185-206 (1999)
Field incidence
Field incidence
Distal Edge
Tracking
Field incidence
2D modulation
Field incidence
2.5 D modulation
3D modulation
IMPT – Example 1 (distal edge tracking)
IMPT – Example 2 (3D modulation)
Treatment planning for IMPT: KonRad TPS (DKFZ)
- Bragg peaks of pencil beams are distributed throughout the
planning volume
- Pencil beam weights are optimized for several beam
directions simultaneously, using inverse planning techniques
- Output of optimization: beam weight maps for diff energies
Intensity Modulated Proton Therapy
• Planning approaches
• Delivery options (MGH plan, other sites)
• Overview of IMPT treatments / development
• Special considerations for IMPT
• IMPT vs. 3D-conformal proton vs. photon IMRT
in the clinic
IMRT delivery with multi-leaf collimators
Proton IMPT with Scanning
Protons have charge 
can be focused,
deflected (scanned)
magnetically!
A proton pencil beam
E.Pedroni (PSI)
Proton IMPT with Scanning
A “layer” is
irradiated by
scanning a pencil
beams across the
volume
E.Pedroni (PSI)
Proton IMPT with Scanning
Several layers
are irradiated with
beams of different
energies
E.Pedroni (PSI)
Proton IMPT with Scanning
Complete treatment:
a homogenous dose
conformed distally and
proximally
E.Pedroni (PSI)
: pencil beam scanning nozzle for MGH
Intensity
Modulated
Beam
Pair of
Quads
Scanning
Magnets
Vacuum
Chamber
Fast
Y
Slow
Z
Beam
monitor
X
• Continuous scanning. Modulation in current and speed.
• Pencil beam spot width (s) at the isocenter: ~4-10 mm
• Several identical paintings (frames) of the same target
slice (layer)
• Max patient field (40x30) cm2
Beam delivery: continuous magnetic scanning in 2D
Beam fluence
variation along
the scan path is
achieved by
simultaneously
varying the beam
current and
scanning speed:
dn dn dx
( x)  /  I / v
dx dt dt
x
Actual scan is ~50 times faster (0.4 sec)
Scan
functions:
degeneracy of
the solution
Intensity Modulated Proton Therapy
• Planning approaches
• Delivery options (MGH plan, other sites)
• Special considerations for IMPT
• Overview of IMPT treatments / development
• IMPT vs. 3D-conformal proton vs. photon IMRT
in the clinic
The effect of delivery
uncertainties in IMPT:
fluctuations in the beam
position during the scan
planned dose distr
plan
delivery
dose difference due to fluct’s
Beam size in IMPT
S Safai
Proton dose in the presence of range uncertainty
Proton dose in the presence of range uncertainty
(a dense target)
Lower
proton
dose
IMPT – DET (Distal Edge Tracking)
Tumor
T. Bortfeld
Distal Edge Tracking: Problem with range
uncertainty
Tumor
Brainstem
T. Bortfeld
In-vivo dosimetry / range verification with PET
K. Parodi (MGH)
MGH Radiology
IMPT in the presence of range uncertainties:
DET vs. 2.5D
DET
DET (+1 mm)
DET (+3 mm)
DET (+5 mm)
2.5D
2.5D (+1 mm)
2.5D (+3 mm)
2.5D (+5 mm)
Robust IMPT optimization
J Unkelbach (MGH)
• “Standard” optimization
• Phantom test case
• Robust optimization
Degeneracy of IMRT solution:
different modulation patterns may produce
clinically “equivalent” dose distributions
Proton Treatment
Field
Brass Collimator
M Bussiere, J Adams
Scanning with a range compensator
Scanning and IMPT
• Is scanning = intensity-modulation ?
IMPT delivery:
Spot scanning at PSI (Switzerland)
A Lomax Med Phys (2004)
PSI gantry
radmed.web.psi.ch/asm/gantry/intro/n_intro.html
• Gantry radius 2m
• Rotation (a):185 deg
• “Step-and-shoot” scanning:
200 MeV proton beam is stopped
at regular intervals, no irradiation
between “beam spots”
magnets
sweeper
beam
monitor
quad
range shifter
PSI ProSCAN
Scanning and IMPT
• Is scanning = intensity-modulation ?
• Is beam scanning = IMPT?
Dose conformation with IMPT
3D IMPT
3D-CPT
SFUD – single
field uniform dose
1 field
1 field
1 field
?? 2.5-D IMPT ??
3 fields
3 fields
A Lomax (PSI)
Scanning and IMPT
• Is beam scanning = IMPT ?
• Is scanning = intensity-modulation ?
• Is intensity-modulation = IMPT ?
Spread-Out
Bragg Peak
(SOBP)
Wheel rotates
@ 10 / sec
RM
Spread-Out
Bragg Peak
(SOBP)
Wheel rotates
@ 10 / sec
RM
Spread-Out
Bragg Peak
(SOBP)
Wheel rotates
@ 10 / sec
RM
Beam-current modulation: flat-top SOBP
Beam-current modulation: sharper fall-off
IMPT fields
for a
prostate
treatment
(a)
Double scattering
“IMPT”
(b)
Intensity Modulated Proton Therapy
• Planning approaches
• Delivery options (MGH plan, other sites)
• Special considerations for IMPT
• Overview of IMPT treatments / development
• IMPT vs. 3D-conformal proton vs. photon IMRT
in the clinic
Delivery of IMPT:
Spot scanning at PSI (Switzerland)
• Since 1996:
• Combination of magnetic, mechanical scan
• Energy selection at the synchrotron + range shifter
plates
A Lomax Med Phys (2003)
GSI Darmstadt: scanned carbon beam
© Physics World
D Shardt (GSI)
GSI patient case: Head+Neck
Carbon
Proton (IMPT)
Plan: O. Jaeckel (GSI)
Plan: A.Trofimov (MGH)
Depth scanning at GSI (270 MeV C-ions)
U.Weber et al. Phys.Med.Biol. 45 (2000) 3627-3641
• Weaknesses of lateral
scanning:
– complicated scanning
pattern
– need to interrupt the beam
• Depth scanning:
– Target volume is divided
into cylinders spaced at
~0.7 FWHM (or 4-5 mm)
– Cylinders are filled with
SOBP (or arbitrarily
shaped distribution)
Scanning directions
• Fast scanning in depth (2 sec/cylinder)
• Slower lateral scanning (sweeper magnet)
• Yet slower azimuthal scanning (gantry rotation)
GSI: IMPT with
depth scanning
• Same dose conformity as with lateral scanning
• A simpler, uninterrupted scanning pattern
• Treatment time a factor of 4 longer than with 2D
raster scanning
Proton Therapy Center – MD Anderson CC, Houston
PTC-H
3 Rotating Gantries
1 Fixed Port
1 Eye Port
1 Experimental Port
Pencil Beam Scanning Port
Passive Scattering Ports
Experimental Port
Accelerator System
Large Field Fixed
Eye Port
Hitachi, Ltd.
M. Bues (MDACC)
Basic Design Parameters for PBS at
PTC-Houston
Beam
•
•
•
•
•
•
Step and shoot delivery
Minimum range: 4 cm
Maximum range: 30 cm
Field size: 30 x 30 cm
Source-axis-distance: 250 cm
Spots size in air, at isocenter:
–
–
–
–
4.5 mm for range of 30 cm
5 mm
R=20 cm
6.5 mm
R=10 cm
11 mm
R=4 cm
• Varian Eclipse TPS
3.2m
Beam Profile
Monitor
Scanning
Magnets
Helium
Chamber
Position Monitor
Dose Monitor 1, 2
Isocenter
Hitachi, Ltd.
M. Bues (MDACC)
Intensity Modulated Proton Therapy
• Planning approaches
• Delivery options (MGH plan, other sites)
• Overview of IMPT treatments / development
• Special considerations for IMPT
• IMPT vs. 3D-conformal proton vs. photon IMRT
in the clinic
Clinical relevance of intensity-modulated
therapy (protons vs photons)
Conformality
high
IMPT
3D PT
IMXT
3D CRT
low
Integral dose
J Loeffler, T Bortfeld
• Complex
anatomies/geometries
(e.g., head & neck) with
multiple critical structures
• Cases where Tx can be
simplified, made faster
• Cases where integral
dose is limiting (e.g.,
pediatric tumors)
• Cases where it may be
possible to reduce sidehigh
effects (improve patient’s
quality of life)
Comparative treatment planning
Purpose: to identify sites, tumor geometries that would benefit the
most from a certain treatment modality or technique
3D-CPT
IMPT
Dose [Gy/GyE]
IMXT
J Adams
A Chan (MGH)
Nasopharyngeal carcinoma
Clinical plan: composite proton+X-ray
• BPTC: 12 proton fields
– CTV to 59.4 GyE
– GTV to 70.2 GyE
(33 x 1.8 Gy)
(+ 6 x 1.8 Gy)
• MGH Linac: 4 fields (lower neck, nodes)
to 60 Gy
G
N
N
G
Case 1
J Adams
A Chan (MGH)
IMXT plan
• For delivery on linac with 5-mm MLC
– 6 MV photons
– 7 coplanar beams
Case 2
IMPT plan
• Bragg peak placement in 3D
• Proton beam energies: 80-170 MeV
• 4 coplanar fields
Case 3
Dose-volume histograms
(DVH)
D50
D95
D5
Nasopharyngeal carcinoma: dose to tumor
3D-CPT
Case 2
• Comparable
target
coverage
IMPT
IMXT
(Some) common complications in Head+Neck Tx
• Compromised vision
– Optic nerves, chiasm (“tolerance”: 54 Gy), eye lens (<10 Gy)
• Compromised hearing
– Cochlea (<60 Gy)
• Dysphagia / aspiration during swallowing
– Salivary glands: e.g. parotid (mean <26 Gy)
– Larynx, constrictors, supraglottic, base of tongue
– Suprahyoid muscles: genio-, mylohyoid, digastric
• Xerostomia (dry mouth)
– Salivary glands
• Difficulty chewing, trismus
– Mastication muscles: temporalis, masseters, digastric
• Compromised speech ability
– Vocal cords, arytenoids, salivary glands
Dose-response models:
e.g. parotid gland
Eisbruch et al
(IJROBP 1999)
Saarilahti et al
(Radiother Onc 2005)
Roesink et al
(IJROBP 2001)
Complications may arise from irradiation to
doses well below the organ “tolerance”
Roesink et al. (IJROBP 2001)
Chao et al
(IJROBP 2001)
Treatment planning
for nasopharyngeal carcinoma
• Critical normal structures (always outlined):
– brain stem, spinal cord, optic structures, parotid glands, cochlea
• ‘Extra’ structures were outlined on 3 data sets
– esophagus, base of tongue, larynx
– minor salivary, sublingual and submandibular glands
– mastication and suprahyoid muscles
Nasopharyngeal carcinoma:
sparing of normal structures
• Superior sparing with protons
– Brainstem
– Suprahyoid muscles
– Sublingual, minor salivary glands
Nasopharyngeal carcinoma:
sparing of normal structures (2)
• IMXT/IMPT better than 3D-CPT
– Salivary glands
– Supraglottic structures
Nasopharyngeal carcinoma:
sparing of normal structures (3)
• IMPT may further improve sparing
–
–
–
–
Mastication muscles
Oral cavity, palate, base of tongue
Cochleae
Optic structures, temporal lobes
Nasopharyngeal carcinoma:
sparing of normal structures (4)
• IMPT may further improve sparing
–
–
–
–
Mastication muscles
Oral cavity, palate, base of tongue
Cochleae
Optic structures, temporal lobes
Retroperitoneal sarcoma
C. Chung, T.Delaney
• Radiation dose:
• 50.4 Gy (E) in 1.8 Gy/fx
to 100% of CTV and
›95% of PTV
• Pre-op Boost of 9 Gy (total 59.4 Gy (E))
• Post-op Boost of 16.2 Gy (total 66.6 Gy (E))
• Organ at Risk (OAR) constraints
•
•
•
•
Liver: 50% < 30 GyE
Small Bowel: 90% < 45 GyE
Stomach, Colon, Duodenum: max 50 GyE
Kidney: 50% < 20 GyE
36 yo M with myxoid liposarcoma:Transverse
IMXT
(photon
IMRT)
3D CPT
IMPT
36 yo M with myxoid liposarcoma: Sagittal
IMXT
3D CPT
IMPT
Boost
IMXT
IMPT
PTV Conformity Index
• (CI)= V95% / PTV
Range (N=10)
Mean
IMXT
1.19 – 1.50
1.35
3D CPT
1.37 – 2.34
1.78 (p=0.032)
IMPT
1.05 – 1.30
1.15 (p=0.005)
Dmean to OAR
Dmean to liver
(n=8)
Preop boost
(n=3)
IMXT
0.94 – 24.6 Gy,
mean 11.8 Gy
3D CPT
0.01 – 20.9 Gy,
mean 6.61 Gy (p=0.01)
12.0 – 24.6 Gy,
mean 16.7 Gy
_____
IMPT
0.99 – 18.6 Gy,
mean 5.73 Gy
(p=0.03)
2.8 – 18.6 Gy,
mean 9.2 Gy
Dmean to OAR (2)
IMXT
Dmean to stomach
(n=8)
Preop boost
(n=3)
4.03 – 44.2 Gy,
mean 15.4 Gy
13.3 – 43.6 Gy,
mean 28.4 Gy
_____
3D CPT 0 – 50.0 Gy,
mean 11.8 Gy (p=NS)
IMPT
0 – 36.5 Gy,
mean 7.85 Gy
(p=0.02)
3.5 – 35.2 Gy,
mean 16.8 Gy
• Prostate carcinoma:
(GTV + 5mm) to 79.2 Gy
(CTV + 5mm) to 50.4 Gy
IMRT
(a)
Dose [Gy]
3D CPT
(b)
Dose [CGE]
IMPT
(c)
Dose [CGE]
Prostate: IMRT vs 3D-CPT vs IMPT
Burr Proton Therapy Center (2001-)
Patient Population
•
•
•
•
•
•
Brain
32%
Spine
23%
Prostate
12%
Skull Base
12%
Head & Neck 7%
Trunk/Extremity
Sarcomas 6%
• Gastrointestinal 6%
• Lung
1%
T. DeLaney, MD
IMPT vs. photon IMRT
• More tumor-conformal dose: reduction in dose to healthy
organs (including skin)  (?) increased tumor control,
reduced complications (acute and late).
Proton integral dose smaller (factor 1.5-3)
• Proton dose conformality much better at low and medium
doses, but usually equivalent to IMRT in high-dose range
• Treatment delivered with fewer fields (2-3 vs. 5-7);
Patient-specific devices/QA are not strictly required 
more treatments at lower cost
• Precision of delivery can be increased with robust planning
methods, in-vivo range/dose verification
Acknowledgements
T Bortfeld, PhD
GTY Chen, PhD
T DeLaney, MD
J Flanz, PhD
H Kooy, PhD
J Loeffler, MD
M Bues, PhD
JA Adams
M Bussiere
S McDonald, MD
H Paganetti, PhD
K Parodi, PhD
S Safai, PhD
H Shih, MD
J Unkelbach, PhD
Ion Beam
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