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HST.187: Physics of Radiation Oncology
#5. Intensity-modulated radiation therapy: IMRT and IMPT
Part 2: IMPT
Joao Seco, [email protected]
Alexei Trofimov, [email protected]
Dept of Radiation Oncology MGH
March 6, 2007
IMRT Coll. Work GroupIJROBP 51:880 (2001)
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
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 peakDepth = additional degree of freedom with protons
H.KooyBPTC
A. Lomax: “Intensity modulation methods for proton RT”
Field incidence
Distal Edge Tracking
Field incidence
2D modulation
Field incidence
2.5 D modulation
Field incidence
3D modulation
Phys. Med. Biol. 44:185-206 (1999)
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
A proton pencil beam
Proton IMPT with Scanning
E.Pedroni (PSI)
Protons have charge can be focused, deflected (scanned)
magnetically!
A “layer” is irradiated by scanning a pencil beams across the volume
Proton IMPT with Scanning
E.Pedroni (PSI)
Several layers are irradiated with beams of different energies
Proton IMPT with Scanning
E.Pedroni (PSI)
Complete treatment:a homogenous dose conformed distally andproximally
Proton IMPT with Scanning
E.Pedroni (PSI)
: pencil beam scanning nozzle for MGH
• Continuous scanning. Modulation in current and speed.• Pencil beam spot width () at the isocenter: ~4-10 mm• Several identical paintings (frames) of the same target
slice (layer)• Max patient field (40x30) cm2
Beam monitor
Intensity Modulated
Beam Z
X
Y
Fast Slow
Scanning Magnets
Pair of Quads
Vacuum Chamber
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:
xvIdtdx
dtdn
dxdnx //)(
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 dose difference due to fluct’s
plandelivery
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 protondose
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
DETDET (+1 mm)DET (+3 mm)DET (+5 mm)
2.5D2.5D (+1 mm)2.5D (+3 mm)2.5D (+5 mm)
Robust IMPT optimization
• Phantom test case
• “Standard” optimization
• Robust optimization
J Unkelbach (MGH)
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 gantryradmed.web.psi.ch/asm/gantry/intro/n_intro.html
• Gantry radius 2m • Rotation 185 deg• “Step-and-shoot” scanning:
200 MeV proton beam is stopped at regular intervals, no irradiation between “beam spots”
magnets
range shifter
beammonitor
sweeper
quad
PSI ProSCAN
Scanning and IMPT
• Is scanning = intensity-modulation ?
• Is beam scanning = IMPT?
1 field
SFUD – single field uniform dose
Dose conformation with IMPT
1 field
3 fields
3D IMPT3D-CPT
1 field
3 fields
A Lomax (PSI)
?? 2.5-D IMPT ??
Scanning and IMPT
• Is beam scanning = IMPT ?
• Is scanning = intensity-modulation ?
• Is intensity-modulation = IMPT ?
Spread-Out Bragg Peak (SOBP)
RM
Wheel rotates @ 10 / sec
Spread-Out Bragg Peak (SOBP)
RM
Wheel rotates @ 10 / sec
Spread-Out Bragg Peak (SOBP)
RM
Wheel rotates @ 10 / sec
Beam-current modulation: flat-top SOBP
Beam-current modulation: sharper fall-off
IMPT fields for a prostate treatment
(a)
(b)
Double scattering “IMPT”
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
D Shardt (GSI)
© Physics World
GSI patient case: Head+NeckCarbon 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
Passive Scattering Ports
Pencil Beam Scanning Port
Large Field Fixed Eye Port
Experimental Port
Accelerator System
PTC-H3 Rotating Gantries1 Fixed Port1 Eye Port1 Experimental Port
Hitachi, Ltd.
M. Bues (MDACC)
Basic Design Parameters for PBS at PTC-Houston
• 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
Beam3.2m
Scanning Magnets
Beam Profile Monitor
Helium Chamber
Position MonitorDose 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)
Co
nfo
rmal
ity
Integral dose
high
low high
3D CRT
IMXT3D PT
IMPT
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 side-effects (improve patient’s quality of life)
Comparative treatment planning
3D-CPT IMPT IMXT
Dose [Gy/GyE]
Purpose: to identify sites, tumor geometries that would benefit the most from a certain treatment modality or technique
J AdamsA Chan (MGH)
Nasopharyngeal carcinomaClinical plan: composite proton+X-ray• BPTC: 12 proton fields
– CTV to 59.4 GyE (33 x 1.8 Gy) – GTV to 70.2 GyE (+ 6 x 1.8 Gy)
• MGH Linac: 4 fields (lower neck, nodes) to 60 Gy
Case 1
NN
G
G
J AdamsA Chan (MGH)
IMXT plan
• For delivery on linac with 5-mm MLC – 6 MV photons – 7 coplanar beams
Case 2
• Bragg peak placement in 3D
• Proton beam energies: 80-170 MeV
• 4 coplanar fields
Case 3
IMPT plan
Dose-volume histograms (DVH)
D50
D5D95
Nasopharyngeal carcinoma: dose to tumor 3D-CPT IMPT IMXTCase 2
• Comparable target coverage
(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
Saarilahti et al (Radiother Onc 2005)
Eisbruch et al (IJROBP 1999)
Roesink et al (IJROBP 2001)
Chao et al (IJROBP 2001)
Complications may arise from irradiation to doses well below the organ “tolerance”
Roesink 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
• IMPT may further improve sparing– Mastication muscles– Oral cavity, palate, base of tongue– Cochleae– Optic structures, temporal lobes
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)
Retroperitoneal sarcomaC. 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
12.0 – 24.6 Gy,
mean 16.7 Gy
3D CPT 0.01 – 20.9 Gy, mean 6.61 Gy (p=0.01)
_____
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)
Dmean to stomach
(n=8)
Preop boost
(n=3)
IMXT 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
(a)
Dose [Gy]
(b)
Dose [CGE]
(c)
Dose [CGE]
3D CPT
IMRT
IMPT
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
JA AdamsM BussiereS McDonald, MDH Paganetti, PhD
K Parodi, PhD
S Safai, PhD
H Shih, MD
J Unkelbach, PhD
Ion Beam Applications
M Bues, PhD