hst.187: physics of radiation oncology #5. intensity-modulated radiation therapy: imrt and impt part...

HST.187: Physics of Radiation Oncology

#5. Intensity-modulated radiation therapy: IMRT and IMPT

Part 2: IMPT

Joao Seco, PhDjseco@partners.org

Alexei Trofimov, PhDatrofimov@partners.org

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