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Indra J. Das/ Small Fields (Page-1)
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, FASTRODepartment of Radiation OncologyIndiana University School of MedicineIndianapolis, Indiana, USA IJDas (2)
403530252015100.80
0.82
0.84
0.86
0.88
0.90
0.92
0.94
0.96
0.98
1.00
1.02
WEHU-ArizonaTemple UU PennErlanger 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
IJDas (3)
403530252015100.80
0.82
0.84
0.86
0.88
0.90
0.92
0.94
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)
Cone
Fac
tor (
St)
Das et al, J Radiosurgery, 3, 177-186, 2000
Dosimetric Variation with Detectors
14%
IJDas (4)
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
IJDas (5)Das et al, Med. Phys. 35, 206-215, 2008
Definition of Small Fields
IJDas (6)
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 sizescm---- 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
gyFl
uenc
eSc
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
Indra J. Das/ Small Fields (Page-2)
IJDas (7)
Source Size
Jaffray et al, Med Phys 20, 1417-1427 (1993)90%, 70%, 50%, 30%, 10% iso-intensity line
IJDas (8)
Varian TrueBeam
Sawkey et al, Med Phys, 40, 332, 2013
Dimensionsx, y (mm)0.9, 0.7
0.8, 0.7
0.9, 0.9
0.9, 0.8
T2 T3T1
6 MV
6 MVFFF
10 MV
10 MVFFF
Source Size, Modern Machines
IJDas (9)Alfonso, et al. Med Phys 35, 5179-5186 (2008)
IAEA/AAPM Proposed Pathway
IJDas (10)
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
MM
DD
msrclinmsrclin
ffQQkM
MDD ,
,2
1
2
1
IJDas (11)
Relative Dosimetry
rel
relf
Qf
Q
fQ
fQff
QQ adingOutput
MDMD
k msrclinmsrclin )(Re
)(//
clin
msr
clin
msr
clin
clin
msr
clin
,w,w
,w,w,,
refmsr
msr
msr
msr
msr
msr
,,,,,
ffQQQoQQoDW
fQ
fQw kkNMD
msrclin
msrclinmsr
msr
clin
clin
msr
msr
msr
msr
clin
clin
clin
clin
msr
msr
clin
clinmsrclin
msrclin
,,
,w
,w
// ff
QQfQ
fQ
fQ
fQ
fQ
fQ
fQ
fQff
QQ kMM
MDMD
MM
msrfmsrairw
fclinfclinairwffQQ PS
PSk msrclin
msrclin
)()(
,
,,,
IJDas (12)
Meaning of k in Micro-Chambers
Indra J. Das/ Small Fields (Page-3)
IJDas (13)
Stopping Power Ratio
IJDas (14)Sanchez-Deblado et al, Phy. Med. Biol., 48, 2081, 2003
Radiological Parameters
IJDas (15) F. Araki, Med. Phys. 33, 2955-2963 (2006).
Cyber Knife Dosimetry
0.5%
IJDas (16)
Correction Factors
Francescon, et al Med Phys 35, 504, 2008
Correction Factor depends on:Field sizeSource size (FWHM)Detector type
IJDas (17)
0.900.920.940.960.981.001.021.041.061.081.101.121.141.16
0 5 10 15 20 25 30 35
Corre
ctio
n fac
tor
Field size (mm)
Siemens; PTW diode 60012Elekta; PTW diode 60012Siemens; Exradin A16Elekta; Exradin A16Siemens; Sun Nuclear Dedge"Elekta; Sun Nuclear Dedge"Siemens; PTW Pinpoint 31014Elekta; PTW Pinpoint 31014Siemens; PTW microLionElekta; PTW microLion
Francescon et al Med Phys,38, 6513, 2011
Published data on
IJDas (18) Med. Phys. 38 (12), 6992, 2011
of Linear Accelerators (Varian)
Indra J. Das/ Small Fields (Page-4)
IJDas (19)
Radiotherapy and Oncology 100 (2011) 429–435
Med. Phys. 38 (12), 6513-6527, 2011
of Linear Accelerators
IJDas (20)
Cyber Knife
Pantelis et al, Med Phy. 37, 2369-2379, 2010
IJDas (21)
CyberKnife data
-12-10-8-6-4-202468
1012
PinPoint Diamond(old) EBT2 MicroTLD IBA-SFD PTW Diode SN-Edge
Unc
orre
cted
out
put d
iffer
ence
(%)
with
MC
Moignier et al, Med Phys 41(7), 071702, 2014
5 mm cone
IJDas (22)
IJDas (23)
Med Phys, 41(4), 041711, 2014
IJDas (24)
Newer Data on
Benmakhlouf et al, Med Phys, 41(4), 041711, 2014
Indra J. Das/ Small Fields (Page-5)
IJDas (25)
New Published data From IAEA
IJDas (26)
Correction Factors
IJDas (27) IJDas (28)
Correction in Profile (OAR)
Francescon et al, Med Phys, 41(10), 101708, 2014
5 mm cone 25 mm cone
IJDas (29) Sham et al, Med Phys, 35, 3317-3330, 2008
Depth Dose & Source Size
IJDas (30)
Papaconstadopoulos, et al, Phys. Med. Biol. 59 (2014) 5937–5952,
Good News with Modern Microdetectors
Indra J. Das/ Small Fields (Page-6)
IJDas (31) IJDas (32)
Machine, Cone & Depth?
Radiotherapy Oncology, 112, 442-446, 2014
IJDas (33)
0.00.10.20.30.40.50.60.70.80.91.01.1
0 1 2 3 4 5 60.00.10.20.30.40.50.60.70.80.91.01.1
0 1 2 3 4 5 60.00.10.20.30.40.50.60.70.80.91.01.1
0 1 2 3 4 5 60.00.10.20.30.40.50.60.70.80.91.01.1
0 1 2 3 4 5 6
Validity of Proposed Method
Field Size (cm)
Rela
tive d
ose
at d
max
IJDas (34)
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
IJDas (35)Thanks