small field dosimetry: overview of aapm tg-155 and the iaea...
TRANSCRIPT
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IJDas (1) Wildflower, Panama
Small Field Dosimetry: Overview of AAPM TG-155 and the IAEA-AAPM Code of Practice (Therapy)
Indra J. Das, PhD, FAAPM, FACR, FASTRO Department of Radiation Oncology Indiana University School of Medicine
Indianapolis, Indiana, USA
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IJDas (2)
40353025201510
0.80
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0.84
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0.90
0.92
0.94
0.96
0.98
1.00
1.02
WEHU-ArizonaTemple UU Penn
Erlanger Serago et al.
Fan et al.
Zhu et al.
Total scatter factor from different institutions
Cone Diameter (mm)
Cone
Fac
tor
(St)
Das et al, J Radiosurgery, 3, 177-186, 2000
Small Field Dosimetry Problem
Institutional
variability in 6 MV
Radionics SRS
dosimetry
12% diff
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40353025201510
0.80
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0.92
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0.96
0.98
1.00
Pinpoint (par)
Pinpoint (per)
0.125ion(par)
0.125ion(per)
Diamond
TLD
MC(1mm)
MC(5mm)
CEA (Film)Kodak(Film)
Total scatter factor with various detectors
Cone Diameter (mm)
Co
ne
Fa
cto
r (S
t)
Das et al, J Radiosurgery, 3, 177-186, 2000
Dosimetric Variation with Detectors
14%
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What is a Small Field?
Lack of charged particle
Dependent on the range of secondary
electrons
Photon energy
Collimator setting that obstructs the
source size
Detector is comparable to the field size
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IJDas (5) Das et al, Med. Phys. 35, 206-215, 2008
Definition of Small Fields
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1.5 1.0 0.5 0.0 0.5 1.0 1.50.0
0.2
0.4
0.6
0.8
1.0
x cm
2.0x2.0 cm2
Source sizes
cm
---- 0.01 ---- 0.35
---- 0.50
6.5 6.0 5.5 5.0 4.5 4.0 3.50.0
0.2
0.4
0.6
0.8
1.0
x cm
Ener
gy
Flu
ence
Sc
norm
aliz
ed
Energy Fluence Penumbra/Output
1.5 1.0 0.5 0.0 0.5 1.0 1.50.0
0.2
0.4
0.6
0.8
1.0
x cm
1.0x1.0 cm2
1.5 1.0 0.5 0.0 0.5 1.0 1.50.0
0.2
0.4
0.6
0.8
1.0
x cm
0.5x0.5 cm2
Large field
Nyholm et al Radiother Oncol 78, 347, 2006 and Phys Med Biol 51,6245, 2006
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Source Size
Jaffray et al, Med Phys 20, 1417-1427 (1993) 90%, 70%, 50%, 30%, 10% iso-intensity line
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Varian TrueBeam
Sawkey et al, Med Phys, 40, 332, 2013
Dimensions
x, y (mm)
0.9, 0.7
0.8, 0.7
0.9, 0.9
0.9, 0.8
T2 T3 T1
6 MV
6 MV
FFF
10 MV
10 MV
FFF
Source Size, Modern Machines
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IJDas (9) Alfonso, et al. Med Phys 35, 5179-5186 (2008)
IAEA/AAPM Proposed Pathway
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Why So Much of Fuss? Reference (ref) conditions cannot be achieved for most
SRS devices (cyberknife, gammaknife, tomotherapy etc)
Machine Specific reference (msr) needs to be linked to ref
Ratio of reading (PDD, TMR, Output etc) is not the same
as ratio of dose
2
1
2
1
M
M
D
D
msrclinmsrclin
ff
QQkM
M
D
D ,,
2
1
2
1
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Relative Dosimetry
rel
rel
f
Q
f
Q
f
Q
f
Qff
QQading
Output
MD
MDk msrclin
msrclin )(Re
)(
/
/
clin
msr
clin
msr
clin
clin
msr
clin
,w,w
,w,w,
,
re fm s r
m s r
m s r
m s r
m s r
m s r
,
,,,,
ff
QQQ oQQ oD W
f
Q
f
Qw kkNMD
msrclin
msrclinmsr
msr
clin
clin
msr
msr
msr
msr
clin
clin
clin
clin
msr
msr
clin
clinmsrclin
msrclin
,
,
,w
,w
/
/ff
QQf
Q
f
Q
f
Q
f
Q
f
Q
f
Q
f
Q
f
Qff
QQ kM
M
MD
MD
M
M
msrfmsrairw
fclinfclinairwff
QQPS
PSk msrclin
msrclin
)(
)(
,
,,
,
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Meaning of k in Micro-Chambers
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Stopping Power Ratio
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Sanchez-Deblado et al, Phy. Med. Biol., 48, 2081, 2003
Radiological Parameters
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IJDas (15) F. Araki, Med. Phys. 33, 2955-2963 (2006).
Cyber Knife Dosimetry
0.5%
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Correction Factors
Francescon, et al Med Phys 35, 504, 2008
Correction Factor depends on: Field size
Source size (FWHM)
Detector type
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0.90
0.92
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0.96
0.98
1.00
1.02
1.04
1.06
1.08
1.10
1.12
1.14
1.16
0 5 10 15 20 25 30 35
Co
rrec
tio
n fa
cto
r
Field size (mm)
Siemens; PTW diode 60012
Elekta; PTW diode 60012
Siemens; Exradin A16
Elekta; Exradin A16
Siemens; Sun Nuclear Dedge
"Elekta; Sun Nuclear Dedge"
Siemens; PTW Pinpoint 31014
Elekta; PTW Pinpoint 31014
Siemens; PTW microLion
Elekta; PTW microLion
Francescon et al Med Phys,38, 6513, 2011
Published data on
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IJDas (18) Med. Phys. 38 (12), 6992, 2011
of Linear Accelerators (Varian)
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Radiotherapy and Oncology 100 (2011) 429–435
Med. Phys. 38 (12), 6513-6527, 2011
of Linear Accelerators
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Cyber Knife
Pantelis et al, Med Phy. 37, 2369-2379, 2010
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CyberKnife data
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
12
PinPoint Diamond(old) EBT2 MicroTLD IBA-SFD PTW Diode SN-Edge
Unco
rrec
ted o
utp
ut
dif
fere
nce
(%
)
wit
h M
C
Moignier et al, Med Phys 41(7), 071702, 2014
5 mm cone
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Med Phys, 41(4), 041711, 2014
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Newer Data on
Benmakhlouf et al, Med Phys, 41(4), 041711, 2014
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New Published data From IAEA
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Correction Factors
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Correction in Profile (OAR)
Francescon et al, Med Phys, 41(10), 101708, 2014
5 mm cone 25 mm cone
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IJDas (29) Sham et al, Med Phys, 35, 3317-3330, 2008
Depth Dose & Source Size
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Papaconstadopoulos, et al, Phys. Med. Biol. 59 (2014) 5937–5952,
Good News with Modern Microdetectors
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Machine, Cone & Depth?
Radiotherapy Oncology, 112, 442-446, 2014
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0.0
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0 1 2 3 4 5 6
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0 1 2 3 4 5 6
Validity of Proposed Method
Field Size (cm)
Rel
ativ
e dose
at
dm
ax
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Summary
Understand the limit of small field
Focal spot issues
Detectors that are water equivalent like,
MicroLion, MicroDiamond and Plastic
Scintillators are best suited
Use proper correction factors to correct
detector response to correct for the dose
Watch for IAEA and TG-155 guidelines
when they are published
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AAPM-2015/
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What is a “small field” in photon beam dosimetry?
Sam Question # 1
63%
4%
2%
25%
6% A. Less than 3x3 cm2
B. Less than 2x2 cm2
C. Depends on type of machine (CyberKnife, Gamma Knife, etc)
D. Depends on detector (pinpoint, microdiamond, micro-diode etc)
E. Depends on beam energy and source size
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Sam- Answer
Answer: E - Depends on Beam Energy and Source Size
Ref: “Das et al, Small fields: Non-equilibrium radiation
dosimetry," Med Phys 35, 206-215 (2008)
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Sam Question # 2
The source size of a linear accelerator is typically?
78%
15%
3%
4%
0% A. 20 mm
B. 10 mm
C. 5 mm
D. 2 mm
E. 1-10 mm, depending on the machine
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Answer: E – Depending on machine
Ref: Jaffray et al, Med Phys 20, 1417-1427 (1993)
Sam- Answer 2
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Sam Question # 3
Dosimetry of small field should be performed with;
A. Small water-equivalent
detectors (MicroLion, MicroDiamond, Plastic Scintillators)
B. Edge detector
C. Pinpoint
D. MicroMosfet
E. Any micro-detector
A. B. C. D. E.
89%
2%
9%
0%1%
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Answer: A – The detectors that are water equivalent
Ref: Azangwe et al, Med Phys 41, 072103 (2014)
Benmakhlouf et al, Med Phys 41, 041711 (2014)
Sam- Answer #3
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IJDas (41) Thanks