Overview of Quality Assurance in Proton Therapy
Omar Zeidan
AAPM 2012
Charlotte, NC
July 30st, 2012
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
2
Clinically operating proton therapy facilities
WA
MT
ME
ND
OR
VT
MN
NH
ID
WI
SD
MI
NY
MA
CT RI
WY
PA
IA
OH
IL
UT
IN
CO
OK
AZ
MD
DE
UPENN
WV
VA
MO
KS
Loma
Linda
University
NJ
NE
NV
CA
Massachusetts
General
Hospital
KY
Midwest Proton
Radiotherapy
TN
Institute
AR
NC
Hampton
University
SC
NM
AL
GA
MS
TX
LA
FL
MD
Anderson
University of Florida
Proton Therapy
Institute
3
1
Multi-room Facilities
FBTR1
IBTR2
IBTR3
GTR4
4
In-room Design
Inclined Beam 2
Inclined Beam 1
Gantry
Fixed Beam
5
Inside Treatment Room
Three major elements of QA:
• Imaging System
• Positioning System
• Beam delivery
6
2
Beam Delivery Techniques
Beam Spreading Techniques
Passive
Scattering
Active
Scanning
vs
Single Scattering
Uniform Scanning (US)
Double Scattering (DS)
Pencil Beam Scanning (PB)
8
PB
US
DS
Beam Delivery Techniques
9
3
Beam Characteristics at Depth
Dosimetric Advantage of PT
11
Coverage at depth: Protons vs Photons
Target
Y. Zheng
12
4
Anatomy of a Spread-Out Bragg Peak (SOBP)
M
distal end
lateral penumbra
distal penumbra
R
40
60
Ref
0
20
Dose (%)
80 90 100
proximal end
0
50
100
Depth (mm)
ICRU 78
150
Tolerances
Flatness within 5%
Symmetry within 3%
Range within 1.5 mm
Modulation within 5 mm
13
Lateral penumbra at depth
10 MV
Uniform Scanning beam data, ProCure - OKC
14
Distal penumbra at depth
Uniform Scanning beam data – ProCure -OKC
15
5
Proton vs. Photon PDDs in presence of heterogenieties
Photons Loss in Fluence
(attenuation)
SAME ENERGY
Protons Loss in Range (Energy)
(degradation)
SAME FLUENCE
16
How to manipulate the SOBP beam?
detector
M
BEAM
x
BEAM
x
x + y =M
BEAM
x+y
17
surface
What can you get from a SINGLE delivery?
beam
Get creative with compensator
design
Get creative with array housing
Ding et al …. 2012
18
6
QA of Patient Devices
10 cm snout
18 cm snout
IBA Universal Nozzle
Nozzle & Snout Design
20
Patient Devices
21
7
Distal end shaping - no compensator
Target
Proton Beam
Aperture
Inhomogeneity (Air Pocket)
22
Distal end shaping – with compensator
Target
Compensator
Aperture
Inhomogeneity (Air Pocket)
23
Patient Device QA
thick for tissue, thin for bone
24
8
Improving QA equipment
25
Output factor measurements
D = 11 cm
Ref. Beam
Patient Aperture
10 cm Aperture
R16M10
26
Output factor dependencies
Other factors:
Field size, snout position, phantom material, dose rate
27
9
Beam QA with 1D Arrays
1D Arrays – How do they compare for PDD measurements?
vs
29
Zebra PDDs
30
10
Monthly Range Trend
IBL3
31
Beam QA with 2D Arrays
Measurements of Flatness & Symmetry
Monthly QA Sheet, IBL2 – Jan 2012
33
11
Monthly Flatness Trend – reference beam
Flatness Trend - July 2010 to June 2011
3.5
3
Flatness X
Flatness (%)
2.5
Flatness Y
2
1.5
1
0.5
0
-0.5
Month
IBL3
34
Monthly Symmetry Trend – reference beam
Symmetry Trend - July 2010 to June 2011
3.5
3
Symmetry (%)
2.5
Symmetry
X
2
1.5
1
0.5
0
-0.5
Month
IBL3
35
ProCure Morning QA Device
rf Daily QA3
Irradiation area
+
fiducials
ProCure Machine Shop
Xiaoning 36
Ding, PhD
12
Imaging QA: Comparing DRR with X-ray Image
X Images
DRR
37
Morning QA Procedure
One setup, One device, One beam
to get the following:
1.
2.
3.
4.
5.
Output consistency check
Range consistency check
Symmetry consistency check
Imaging vs mechanical alignment check
In-room laser check
38
Output Factor
Morning QA Trends
1.04
1.02
1
0.98
0.96
6/1/10
8/16/10
10/31/10
1/15/11
4/1/11
6/16/11
8/31/11
11/15/11
Range (mm)
161.5
161
160.5
160
159.5
159
Symmetry (%)
158.5
7/5/11
4
3
2
1
0
-1
-2
-3
-4
8/20/11
8/5/11
8/30/11
9/9/11
9/5/11
9/19/11
10/6/11
9/30/11
10/10/11
10/20/11
39
13
Temporal tracking of PPS correction vector
Y
X
Z
40
Colinearity Test
•
Purpose: to check that imaging isocenter coincides with radiation
isocenter to within 1 millimeter.
Proton Iso
Imaging Iso
41
Daily Checks
Monthly Checks
Annual Checks
•
•
•
•
Imaging vs mechanical alignment
Output
Range
Software Communication
•
•
•
•
Proton-imaging isocentricity
Flatness & Symmetry
Ranges and Modulations
Mechanical
•
•
•
•
PPDs + Modulations
Combinations of field sizes and gantry angles
X-ray source & detector image characteristics
Dose rate dependencies
42
14
QA Challenges in PT
QA challenges in PT
• 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
44
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
45
15
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
46
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)
47
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
IBA Universal Nozzle
– Modulation (very large combinations)
– Range (very large combination)
48
16
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
49
Contributors
Yuanshui Zheng
Xiaoning Ding
Anthony Mascia
Eric Ramirez
Yixiu Kang
Wen Hsi
50
Thank you
51
17