Chapter27-BWiney · IMRT 26.8 34

transcript

6/5/15

Small Field Dosimetry, SRS and Eyes Brian Winey, PhD

Massachusetts General Hospital Harvard Medical School

Small Field Dosimetry

§  Small Field Definition: §  Primary limitation is lateral

disequilibrium

§  Range dependency

§  Shallow ranges (<4 cm), lateral disequilibrium occurs d < 1 cm

§ Deeper ranges, lateral disequilibrium occurs at larger field sizes

§  Measurements are more difficult §  Volume effects and increase penumbra

§ Multiple proposed methods

§  Ion chambers, MLICs, parallel chambers, diamond, film, diodes, etc.

§  Limitations of devices already presented

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Most Common Measurements

§  Small/Micro IC (ex: PTW Pinpoint, others) §  PDD (CAX, OAX), Absolute Dose

§ Cross calibrated against standards

§  Saturation in Scanned beams

§  Parallel chambers: §  Integrated Depth Dose

§  MLIC: §  Integrated Depth Dose

Most Common Measurements

§  Film: §  Planar Doses

§  LET and Calibration

§  Diodes and Diamond: §  Point Doses, especially for very small fields

§ Cross calibration with IC in larger Field at same depth

§  LET and drifting

Small Field Chambers/Diodes:

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Small Field Characteristics

§  Penumbra Increases with range

§  Increased lateral penumbra affects the CAX for smaller fields

§  Reduces the Bragg peak due to multiple coulomb scatter and geometry/beam optics for aperture collimation

Penumbra:

§  Sharper at Shallow Depths

§  Less Sharp at Greater Depths

§  All 16cm/1cm (R/M) and entrance dose

§  Penumbra Increases

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Small Field Dosimetry: PDD

Small Field Dosimetry: IDD

Similar to Plane Parallel Chamber Measurements

Field Size Effects: Output

J. Daartz, MGH

Greatest effects: Large Depth, Small Field

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SRS History

§  Gamma Knife original photon treatment (1950’s)

§  Ten years later (1960’s): proton radiosurgery

§  Linac based begun in 1980’s and Cyberknife later

§  Thousands of patients treated with Photon SRS—clinically proven technique

Why Proton SRS?

§  Generally with respect to photon SRS § Distal Edge

§  Integral Dose

§ Higher TCP/Lower NTCP

History of Proton Radiotherapy §  1947: R. Wilson proposes

using protons for radiotherapy

§  1954: First patient treated with protons at Berkeley

§  1960+: Kjellberg studies and applies protons for neurological tumors §  1st HCL patient: 2yo with supra-

pituitary mass

§  Many reports since…

R. Wilson, Ph.D.

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History of Proton Radiotherapy

§  HCL II

§  Physics Lab

R. Wilson, Ph.D.

HCL in the 1960-70’s

R. Wilson, Ph.D.

§  Seated patients, orthogonal kV imaging

§  Invasive Frame

STAR §  STereotactic Alignment for Radiosurgery

§  Alignment system designed for fixed beam delivery system at HCL (1991)

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STAR §  STereotactic Alignment for Radiosurgery

§  Positioner was moved to MGH in 2001

§  New Beam Line: §  Single Scattering System, optimized for

Cranial Proton Radiotherapy

§  Single Scattering: § Smaller Penumbra

§ Higher Dose Rates § Limited Field Size

§  Also treat on Gantries!

Proton Therapy Center at MGH

Francis H. Burr Proton Therapy Center - STAR beamline

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Dose Calculations

§  TPS (XiO): RC/Aperture Calculations §  Range/Mod Calculations

§  Laminate Program Calculates Feasible R/M with BABS

TARGET

Patient Specific Target Range

Modulation d90-p90

§  Generally Use 90% Normalization §  Sharper Penumbra §  Less Ripples (Hot/Cold Spots)

§  Like Photon SRS: No PTV—discussion topic

§  Doses (CGyE) similar to Photon SRS (except AVM)

Patient and field specific hardware

Aperture Range Compensator

Lateral conformation

Distal conformation

Martijn Engelsman, Ph.D.

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Dose Calculations

§  TPS: RC/Aperture Calculations §  Range/Mod Calculations

§  Laminate Program Calculates Feasible R/M with BABS

§  Laminate Program Calculates MU using output model

§  Field Size Correction applied to output

STAR QA/QC Weekly: Range, Modulation, Output, Alignment

Ψ = ao ( 1 + a1 (R/M – 1)a2 ) × ( 1 + a3 R2 + a4 R + a5 )

Zebra (MLIC)

STAR QA/QC Monthly: Flatness, Symmetry, Comprehensive Alignment, X/P Coincidence

-60 -40 -20 0 20 40 600

lateral distance [mm]

horizontalvertical

100 150 200 250

1difference:hor: 0.19mmver: 0.10mm

red: xhair center, black: proton field center

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STAR Daily QA/QC Daily: Range, Modulation, Output, Beam Steering Constancy

IC1 IC2/3 Steering/hardware

T1 Output

RV Range

ALL BABS Layers Tested Weekly

STAR Daily QA/QC Daily: Range, Modulation, Output, Beam Steering Constancy

Invasive Fixation (1960’s-2004)

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Non-Invasive Fixation

Immobilization: Conventional GTC vs mGTC

-2 -1 0 1 20

CC (mm)

Counts

-2 -1 0 1 20

LAT (mm) -2 -1 0 1 20

AP (mm)

-2 -1 0 1 20

Rotation (deg)

Counts

-2 -1 0 1 20

Roll (deg)-2 -1 0 1 20

Pitch (deg)

Intrafraction Motion

B Winey, J Daartz, F Dankers, M Bussiere

J Appl Clin Med Phys 2012 May 10; 13(3)

Immobilization precision of a modified GTC frame

Immobilization: mGTC Efficacy

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Patient Alignment: Fiducials

Most difficult point in the patient workflow.

Patient Setup §  Implanted Fiducials Localized in TPS §  Iso and Fiducials sent to Imaging

System

§  Simple Ray-Tracing backprojection

Why Proton SRS?

§  Costs?

§  Uncertainties?

§  Benefits?

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Costs?

§  Billing is the same as photon SRS

§  Add a proton modifier

§  No Additional cost versus photon

Uncertainties?

§  Range uncertainties (CT, SPR, Motion, Setup, Geometric Patient Daily Variations)

§  Motion-Miss Targets

§  Field Size Effects

§  Penumbra

§  Online Imaging Limited

§ ∴ Affect the conformality (Rx dose)

Proton range changes (Cranial SRS)

§  Fluids in sinuses §  Scattering from heterogeneities §  Setup Uncertainties §  Air gap

Lei Dong, Ph.D.

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Proton range changes: Cranial SRT §  Fluids in sinuses §  Scattering from heterogeneities §  Setup Uncertainties §  Air gap §  Onyx for AVM

§  Artifacts § WET

Lei Dong, Ph.D.

Patient Setup §  Implanted Fiducials Localized in TPS §  Simple Ray-Tracing backprojection

§  Or 2D/2D anatomic markers

Setup Uncertainties

§  Externally verified 2D/3D registration algorithm (Reg23)

Steininger, et.al. PMB, 2012, 57, 4277-4292.

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-1 0 10

Δ X (mm)-1 0 10

Δ Y (mm)-1 0 10

Δ Z (mm)0 1 20

Δ R (mm)

-1 0 10

Δ RX (deg)-1 0 10

Δ RY (deg)-1 0 10

Δ RZ (deg) !

-2 0 20

Δ X (mm)-2 0 20

Δ Y (mm)-2 0 20

Δ Z (mm)0 1 20

Δ R (mm)

-2 0 20

Δ RX (deg)-2 0 20

Δ RY (deg)-2 0 20

Δ RZ (deg)

-5 0 50

Δ X (mm)-5 0 50

Δ Y (mm)-5 0 50

Δ Z (mm)0 5 100

Δ R (mm)

-5 0 50

Δ RX (deg)-5 0 50

Δ RY (deg)-5 0 50

Δ RZ (deg)

STAR: Fiducials Gantry: Fiducials

Gantry: Anatomy

Intrafractional Motion

Cranial Intrafractional Motion

Impact on MFO Planning Less impact on Passive Scattered

Lei Dong, Ph.D.

Positioning Summary

Patient positioning coordinate

Fiducial-based patient positioning

Anatomy-based patient positioning

left/right 0.74 1.12superior/inferior 0.73 1.57

anterior posterior 0.85 1.18pitch 0.64 1.02roll 0.55 1.64yaw 0.39 0.89

Positioning uncertainty (mm / deg)

Patient setup positioning uncertainties at the Francis H. Burrproton therapy center of the MGH.

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1.5 mm setup error

Worst Case

Pituitary Adenoma: Effects were due to lateral shifts and range uncertainties.

Uncertainty Mitigation §  What do we do with all of this

information: § Margins: Distal/Proximal

§  Beam angle selection

§  Smearing

§  Feathering

§ Gating

§ OARs

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Typical Planning (PBS)

§  Multiple Studies to account for uncertainties in planning

§  Robust optimization

§  Beam specific margins (only SFUD) §  Preprocessing

§ Online

Beam Angle Selection

1. Avoid beam entrance angles along and through heterogeneous boundaries 2. Avoid distal edge sparing. 3. Use multiple beams to reduce uncertainty of a single beam!

OARs §  AVOID distal edge sparing!

§  If unavoidable, use multiple fields to spread the risk and reduce the dose to the OAR if there is an error.

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Using Multiple Beams

§  Spreads uncertainty due to range, patient setup, LET, and patient motion

§  Difference in lateral and distal uncertainties

§  Increases conformality for both scanned and scattered delivery

§  Increased Robustness

Proton SRS Treatment Planning Summary

§  Field Size/MCS

§  Beam positions

§  Heterogeneities

§  Penumbra Regions

§  Distal Positions

§  LET/RBE

§  More beams à More Conformal/Less Uncertainties from single beam

Why Proton SRS?

§  Benefits: § Distal Edge

§  Penumbra

§  Integral Dose

§ Higher TCP/Lower NTCP

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Still have the Bragg Peak! §  Primary ‘physics’ advantage over photons:

Bragg Peak

0 50 100 150 200 250 300

Energy (MeV)

Source: NIST database

p+ Beam Range = 15 cm

Integral Dose

Integral Dose §  The V40% for protons is smaller

than photons

§  Due to the incorporation of uncertainties in planning, the conformality is tighter with photons for most SRS targets

§  Abnormally shaped targets or targets close to an OAR can have tighter conformality

§  Clinical Significance?

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Proton SRS for Benign Cases: Secondary Cancer Risks

Risk of 2nd cancer Clinical symptomsEUD (Gy) NTCP (%) EUD (Gy) NTCP (%) NTCP (%)

SRT 32.1 23 <0.1 28 <0.1 <0.12-field photon 5.7 48 1.3 48 1.2 133-field photon 11.2 38 <0.1 40 0.1 2IMRT 26.8 34 <0.1 37 <0.1 12-field proton 1.5 30 <0.1 35 <0.1 <0.13-field proton 4.3 29 <0.1 35 <0.1 <0.14-field proton 6.1 27 <0.1 34 <0.1 <0.15-field proton 6.8 26 <0.1 34 <0.1 <0.1

Right temporal lobe Left temporal lobeRadiographic changes

Acoustic àà Sarcomatous Hanabusa, 2001 Acoustic àà Glioblastoma Shamisa, 2001 AVM àà Glioblastoma Kaido, 2001 Acoustic àà Meningiosarcoma Thomsen, 2000 NF2 àà Malig n. sheath (3 cases) Baser, 2000 NF2 àà malignant meningioma Baser, 2000 NF2 àà Malignant ependymoma Baser, 2000 Mening àà Glioblastoma Yu, 2000 Acoustic àà Malig Schwannoma Shih, 2000 Cav hem àà Glioblastoma Salvati, 2003 Acromeg àà Meningioma Loeffler, 2003 Acromeg ààVestibular Schwannoma Loeffler, 2003 AVM àà Meningioma Sheehan 2006 Many more studies…

Winkfield, et al, 2011

Triage: Which Patients to Treat

§  Benign Neoplasms: §  Acoustic Neuromas § Meningiomas §  Pituitary Adenomas

§  Arteriovenous Malformations §  Metastatic Lesions

§ Multiple Lesions § Close proximity to surface or critical

structures (optics, brainstem)

PROTON SRS CASES Caseload

15%11%

AVMAcousticPituitaryMeningiomaOtherExtracranial

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Proton SRS Examples

§  Pituitary Adenoma §  Atypical Meningioma (multiple sites) §  Single Meningioma §  Acoustic Neuroma §  Arteriovenous Malformation §  Large Met Near Optics §  Multiple Mets §  Comparisons to Photons are only for Linac

Pituitary Adenomas, 18-20Gy

Endocr Pract 2007 Nov-Dec 13(7)

Proton Stereotactic radiosurgery in management of persistent acromegaly

Petit, Biller, Coen, Swearingen, Ancukiewicz, Bussiere, Chapman, Klibanski, Loeffler

Clin Neurosurg 2008; 55

Management of recurrent and refractory Cushing’s disease with reoperation and/or proton beam radiosurgery

Aghi, Petit, Chapman, Loeffler, Klibanski, Biller, Swearingen

Patient 1 – Pituitary Adenoma

Patient 2 – multiple atypical meningioma

Protons: 10 fields

X-Rays: 12 dynamic arcs

Atypical Meningioma, 12-18 Gy

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Protons X-Rays

Patient 2 – multiple atypical meningioma

Atypical Meningioma, 12-18 Gy

Meningioma, 12Gy

Int J Radiat Oncol Biol Phys 2011 Dec 1; 81(5)

Proton stereotactic radiosurgery for the treatment od benign meningiomas

Halasz, Bussiere, Dennis, Niemierko, Chapman, Loeffler, Shih

Patient 3 – meningioma

Protons X-Rays

Patient 4 –meningioma

Meningioma, 12Gy

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Patient 5 – 4.2 cc acoustic neuroma ( 30 x 180 cGy)

Protons: 4 fields 6 MV X-Rays: 3 dynamic arcs

Acoustic Neuroma, 54Gy in 30 fx

Patient 5 – 4.2 cc acoustic neuroma ( 30 x 180 cGy) Protons X-Rays

Int J Radiat Oncol Biol Phys 2002 Sep 1; 54(1)

Proton beam stereotactic radiosurgery of vestibular schwannomas

Harsh, Thornton, Chapman, Bussiere, Rabinov, Loeffler

Neurosurgery 2003 Sep; 53(3)

Proton beam radiosurgery for vesibular schwannoma: tumor control and cranial nerve toxicity

Weber, Chan, Bussiere, Harsh, Ancukiewicz, Barker, Thornton, Martuza, Nadol, Chapman, Loeffler

Patient 6 – Acoustic Neuroma (Single Fx)

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AVM, 12-16Gy in 1 or 2 fx’s

J Neurosurg 2003 Aug 99(2)

Dose-volume prediction of radiation-related complications after proton beam radiosurgery for cerebral arteriovenous malformations

Barker, Butler, Lyons, Cascio, Ogilvy, Loeffler, Chapman

Int J Radiat Oncol Biol Phys 2012 Jun 1; 83(2)

Planned two-fraction proton beam stereotactic radiosurgery for high-risk inoperable cerebral arteriovenous malformations

Hattangadi, Chapman, Bussiere, Nimierko, Ogilvy, Rowell, Daartz, Loeffler, Shih

Astro Abstract 2012

Proton Beam Stereotactic Radiosurgery for inoperable cerebral ateriovenous malformations.

Hattangadi

Patient 7 – Arteriovenous Malformation

Patient 8 – multiple mets

Protons: 5 fields

X-Rays: 11 arcs

Brain Mets, All, 18Gy in 1 fx

Protons X-Rays

Patient 8 – 4 mets

Brain Metastasis, 18Gy in 1 fx

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Patient 9 – 5 cc met close to optics

Protons: 3 fields 6 MV X-Rays: 6 dynamic arcs

Large Met, 4x 5 Gy

Protons X-Rays

Patient 9 – 5.0 cc met close to optics

Large Met, 4x 5 Gy

Brain Metastasis, 18Gy in 1 fx

Patient 10: Met Close to Optics

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Scanning Example

§  Excellent local control, especially when tumors are too deep for brachytherapy

§  Slightly higher vision preservation

§  Many ocular proton therapy patients

§  Requires lower energies and smaller accelerators

§  Many centers use EyePlan

§  Discussions regarding the future of ocular treatment planning

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Ocular Therapy

§  Tumor dimensions obtained by ultrasound and ophthalmoscopy

§  Some centers evaluating CT and MR

§  Localized based upon anatomic landmarks (ex. optic disk or limbus)

§  Dimensions of the eye

also recorded

Ocular Therapy

§  Radio-opaque clips are attached to the outside of the eye in close proximity to the target

§  The locations are documented

Ocular Therapy

§  Dimensions transferred to EyePlan

§  Margins are added (2-4 mm)

§  Aperture and R/M

calculated

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Ocular Therapy

§  Treatment setup is with clips and radiographs

§  Monitor the retina with video

Ocular Therapy

§  Measurements: Typically with micro ICs, diodes, and MLICs

§  Minimal field size effects due to shallow ranges

§  Diodes for small fields and cross calibrated at larger fields

Ocular Therapy

§  CT based treatment planning

§  Less special hardware

§  Routine TPS

§  Challenges: Reproducibility, eye positioning, intra-fx monitoring, beam commissioning, small range (absorbers)

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Onward… §  More Robust Treatment Planning

§  Better Imaging: §  Real Time

§  Proton Range Information

§  Better probabilistic models

§  Clinical Trials

Robustness

§  Include probability estimates in the treatment planning optimization

§  Reduce high gradients in close proximity to OARs

§  Include Range Uncertainties, Setup Uncertainties, and Motion

5 mm overshoot

C2 chordoma: Rx = 77.4 Gy(RBE)

Trofimov et al

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Robust optimization (illustration)

robust IMPT Standard IMPT

(Trofimov et al 2012)

Robust optimization (illustration)

no-uncertainty plan §  high gradients

robust against range errors

§  reduced gradients

Unkelbach et al 2009

Imaging

§  IBA CBCT

§  MedPhoton

§  2D/3D

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PET Range Verification

0 50 100 150 200 250 3000

Depth (mm)

MC_PA MC_LL MC_PA+LL NeuroPET

Protons

Beam Range (155 mm)

Protons activate carbon and oxygen nuclei that decay by positron emission.

Chul Hee Min, MGH

Summary §  Small Fields can be useful for multiple

treatment sites in proton therapy

§  Challenges remain for accurate measurements

§  Proton SRS is a viable option for cranial SRS

§  Benign cases probably have the most benefits with protons à Integral Dose

§  Currently, less conformal due to uncertainties: §  Online range verification §  Robust planning

§  Patient Imaging

§  Ocular Proton Therapy has high LC §  Challenges of TPS and clinical deployment

Thank You!

http://gray.mgh.harvard.edu

Chapter27-BWiney · IMRT 26.8 34

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