1

Omar Zeidan

AAPM 2012

Charlotte, NC

July 30st, 2012

Overview of Quality Assurance in Proton Therapy

2

Learning Objectives

• Understand proton beam dosimetry characteristics and compare them to photon beams

• Familiarize with proton dosimetry QA tools

• Understand challenges in proton therapy QA

3

Clinically operating proton therapy facilities

WA

OR

CA

ID

NV

AZ

UT

MT

WY

CO

NM

TX

OK

KS

NE

SD

ND

MN

IA

MO

AR

LA

MS

AL GA

FL

IL

WI MI

IN

OH

KY

TN

SC

NC

VA

WV

PA

NY

ME

VT

NH

MA

RICT

NJ

MD DE

UPENN

Massachusetts General Hospital

Loma Linda

University

MD Anderson

Midwest Proton Radiotherapy

Institute

Hampton University

University of Florida University of Florida Proton Therapy

Institute

2

4

Multi-room Facilities

FBTR1 GTR4IBTR2 IBTR3

5

In-room Design

Gantry Fixed Beam

Inclined Beam 1 Inclined Beam 2

6

Inside Treatment Room

Three major elements of QA:

• Imaging System

• Positioning System

• Beam delivery

3

Beam Delivery Techniques

8

Beam Spreading Techniques

Single Scattering

Double Scattering (DS)

Uniform Scanning (US)

Pencil Beam Scanning (PB)

vs Active Scanning

Passive Scattering

9

Beam Delivery Techniques

US

DS

PB

4

Beam Characteristics at Depth

11

Dosimetric Advantage of PT

12

Coverage at depth: Protons vs Photons

Target

Y. Zheng

5

13

Anatomy of a Spread-Out Bragg Peak (SOBP)

0 50 100 150

0

2

0

4

0

6

0

8

0 9

0

10

0

Depth (mm)

Dose (

%)

R

M

Ref

dis

tal p

en

um

bra

proximal enddistal end lateral penumbra

ICRU 78

Flatness within 5%

Symmetry within 3%

Range within 1.5 mm

Modulation within 5 mm

Tolerances

14

Lateral penumbra at depth

10 MV

Uniform Scanning beam data, ProCure - OKC

15

Distal penumbra at depth

Uniform Scanning beam data – ProCure -OKC

6

16

Proton vs. Photon PDDs in presence of heterogenieties

Photons ���� Loss in Fluence

(attenuation)

SAME ENERGY

Protons ���� Loss in Range (Energy)

(degradation)

SAME FLUENCE

17

How to manipulate the SOBP beam?

BEAM

x + yBEAM

x + y = M

xBEAM

x

surface

detector

M

18

beam

What can you get from a SINGLE delivery?

Get creative with compensator

design

Get creative with array housing

Ding et al …. 2012

7

QA of Patient Devices

20

Nozzle & Snout Design

18 cm snout

10 cm snout

IBA

Un

ive

rsa

l N

ozz

le

21

Patient Devices

8

22

Distal end shaping - no compensator

Target

Inhomogeneity (Air Pocket)

Proton Beam

Aperture

23

Distal end shaping – with compensator

Compensator

Aperture

Target

Inhomogeneity (Air Pocket)

24

Patient Device QA

thick for tissue, thin for bone

9

25

Improving QA equipment

26

Output factor measurements

10 cm AperturePatient Aperture

Ref. Beam

R16M10

D = 11 cm

27

Output factor dependencies

Other factors:

Field size, snout position, phantom material, dose rate

10

Beam QA with 1D Arrays

29

1D Arrays – How do they compare for PDD measurements?

vs

30

Zebra PDDs

11

31

Monthly Range Trend

IBL3

Beam QA with 2D Arrays

33

Measurements of Flatness & Symmetry

Monthly QA Sheet, IBL2 – Jan 2012

12

34

Monthly Flatness Trend – reference beam

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

Fla

tness (

%)

Month

Flatness Trend - July 2010 to June 2011

Flatness X

Flatness Y

IBL3

35

Monthly Symmetry Trend – reference beam

IBL3

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

Sym

metr

y (

%)

Month

Symmetry Trend - July 2010 to June 2011

SymmetryX

36

ProCure Morning QA Device

+

rf Daily QA3

ProCure Machine Shop

Irradiation area

Xiaoning Ding, PhD

fiducials

13

37

Imaging QA: Comparing DRR with X-ray Image

DRRX Images

38

Morning QA Procedure

One setup, One device, One beam

to get the following:

1. Output consistency check

2. Range consistency check

3. Symmetry consistency check

4. Imaging vs mechanical alignment check

5. In-room laser check

39

Morning QA Trends

158.5

159

159.5

160

160.5

161

161.5

7/5/11 8/5/11 9/5/11 10/6/11

-4

-3

-2

-1

0

1

2

3

4

8/20/11 8/30/11 9/9/11 9/19/11 9/30/11 10/10/11 10/20/11

Sym

metr

y (%

)R

ange (

mm

)

0.96

0.98

1

1.02

1.04

6/1/10 8/16/10 10/31/10 1/15/11 4/1/11 6/16/11 8/31/11 11/15/11

Outp

ut

Facto

r

14

40

Temporal tracking of PPS correction vector

X

Z

Y

41

Colinearity Test

• Purpose: to check that imaging isocenter coincides with radiation

isocenter to within 1 millimeter.

Imaging Iso Proton Iso

42

Daily Checks

• Imaging vs mechanical alignment

• Output

• Range

• Software Communication

Monthly Checks

• Proton-imaging isocentricity

• Flatness & Symmetry

• Ranges and Modulations

• Mechanical

Annual Checks

• PPDs + Modulations

• Combinations of field sizes and gantry angles

• X-ray source & detector image characteristics

• Dose rate dependencies

15

QA Challenges in PT

44

• Proton delivery modes & control systems are complex-more

things to check

• Lack of methodology or forum to exchange ideas that

improves QA processes – very few clinical proton physicists

• PT systems are not robust yet – few years of operations, many bugs

to resolve (software & hardware)

• QA programs highly depend on vendor’s system specs

QA challenges in PT

45

QA Challenges in PT – cont.

• There are currently no task group recommendations for

proton beam QA. Where relevant we follow guidelines from

the following sources:

– IAEA TRS 398

– ICRU 59

– ICRU 78

– TG 40

– TG 142

– Journal publications

• Lack of dedicated commercial QA devices for PT –adaptation of

photon QA devices is necessary

16

46

QA Challenges in PT – cont.

• It takes time to switch, tune, and deliver beam in every room

–QA tasks takes longer compared to linac systems

• Current PT centers have 3-5 rooms with sequentially beam

delivery – beam sharing is necessary

• Cost of proton specific QA equipment

• Multi vendor software/hardware – lack of true integration

47

Anatomy of a linac head

• Carousel (scatterers)

• Magnets

• Jaws (primary)

• Jaws (tertiary)

• Ion chamber

• MLCs

• Light field

• OUTPUT

– Electrons (4-6 energies)

– Photons (1-3 energies)

48

Anatomy of a Nozzle

• Compensator

• Aperture(s)

• Snout with variable positions

• Lollipops

• Modulator wheels (multiple tracks)

• Multiple ion chambers

• Collimators (X-Y)

• X-Y magnets (3 scanning fields)

• Range verifier

• X-ray source

• Scatterers

• Light field

• OUTPUT

– Modulation (very large combinations)

– Range (very large combination)

IBA Universal Nozzle

17

49

Summary

• Proton Therapy Systems are complex and requires specialized equipment

to measure various beam parameters

• It is imperative to make use of commercially available 1D & 2D arrays and

adapt them to PT to check routinely for

• Beam parameters (R,M, Symmetry, Flatness, Output)

• Imaging System

• Robotic positioning System

• Standardization of QA procedures for PT is essential in establishing

tolerance limits

50

Contributors

Yuanshui Zheng

Xiaoning Ding

Anthony Mascia

Eric Ramirez

Yixiu Kang

Wen Hsi

51

Thank you