Monte Carlo Simulation and Validation of a Novel Yttrium-90 Source for Use in a Conformal Superficial Brachytherapy
Device
Brent Rogers, M.S.
Overview
2
Conformal Superficial Brachytherapy Device
Radioactive Source - 90Y
Monte Carlo Simulation - MCNP
Gafchromic Film Measurements
Conclusions
CONFORMAL SUPERFICIAL BRACHYTHERAPY DEVICE
Conformal Superficial Brachytherapy Device
4
RADIOACTIVE SOURCES90Y
Activated by Neutron Bombardmentβˉ Decay 99.983%Q = 2.280 MeVĒβ = 0.934 MeVRCSDA = 1.129 cmt1/2 = 64.1 hours
90Y Source
6
1 mm
2 mm
MONTE CARLO SIMULATIONMCNP
1
10
100
0 0.2 0.4 0.6 0.8 1
r2·D
ose
Rat
e (n
Gy·
cm2 ·
Bq-
1·h-
1)
r (cm)
MCNP ICRU 56
Point Source in an Infinite Water MediumICRU 56
Dmono Monte Carlo (EGS4, ACCEPT)Dpoly = ∫ Dmono dEβStatistical uncertainty ~2%Systematic uncertainty 3-5%
MCNPβ spectrum ICRU 56100 shells*f8 tally (MeV)
8
Ēdeposited ~90%
MCNP vs. ICRU 56 within Ēdeposited ~90%7.35% max difference
3.16 % average difference
0.1 mm
1.0 cm
GAFCHROMIC FILM MEASUREMENTS
1E+04
2E+04
2E+04
3E+04
3E+04
4E+04
4E+04
5E+04
0 250 500 750 1000 1250
Red
Ch
ann
el P
ixel
Val
ue
(16
bit)
Dose (cGy)
Film MeasurementFit95% Confidence Interval
EBT3 Film Calibration
6 MeV electronsRational fit function
X(D) = a + b/(D-c) where X(D) = red channel scanner response
Non-Linear Least Squares FitR2 = 0.9997 Radj
2 = 0.9996
10
0.0E+005.0E-081.0E-071.5E-072.0E-072.5E-073.0E-073.5E-074.0E-074.5E-07
0 0.1 0.2 0.3 0.4 0.5 0.6
Dos
e R
ate
(cG
y s-
1 Bq-
1)
Depth (cm)
MCNP Measurement
90Y Source Depth Dose MeasurementsActivity: 2.5*107 Bq
0.68 mCi
Dmax = 4.6*10-7 cGy/s/Bq
11
Bare Source vs. Tipped Source at the Surface
Bare SourceSlightly narrower profileFaster dose rate
TippedSlightly wider profileSlower dose rate
00.10.20.30.40.50.60.70.80.9
1
-0.5 -0.3 -0.1 0.1 0.3 0.5
Rel
aive
Dos
e
Position (cm)
Measured: Bare Measured: Tipped
MC: Bare MC: Tipped
Bare Source vs. Tipped Source at the SurfaceBareD=9.8 Gy/min/mCi
T[min]=0.11min∙mCi
Gy ∗Dx [Gy]A [mCi]
TippedD=3.89Gy/min/mCi
T[min]=0.28min∙mCi
Gy ∗Dx [Gy]A [mCi]
D(tipped) =40% D(bare)
BareFWHM ≈ 0.18 cm
TippedFWHM ≈ 0.23 cm
Multiple Sources Applied to the Surface with the CSBT Device
14
6 Sources
D = 5.27 Gy/min/mCi
T = 0.19 Dx/Aper Source
6 Sources
D = 4.66 Gy/min/mCi
T = 0.21 Dx/Aper Source
7 Sources
D = 5.05 Gy/min/mCi
T = 0.20 Dx/Aper Source
8 Sources
D = 5.10 Gy/min/mCi
T = 0.20 Dx/Aper Source
Max dose rate is weakly dependent on the number of sources.
CONCLUSIONS
Conclusion
16
Tips decrease the dose rate by 40%
Bare Source Dose Rate ≈ 10 Gy/min/mCi
6, 7, & 8 Source Dose Rate ≈ 5 Gy/min/mCi
Dose rate is independent of the number of sources for many sources.
References
17
Ferreira, C., at al. (2017). A novel conformal superficial high-dose-rate brachytherapy device for the treatment of nonmelanoma skin cancer and keloids. Brachytherapy, 16(1), 215-222. doi:10.1016/
Alexis Lazarine Reed, A. L. (2007). Medical Physics Calculations with MCNP: A Primer. LA-UR-07-4133
Cross, W. G., at al. (1992). Beta-Ray Dose Distributions From Point Sources In An Infinite Water Medium. Health Physics, 63(2), 160-171. doi:10.1097/00004032-199208000-00003
THANK YOU
MCNP Simulation Benchmarking
19
0.1 mm 1 cm
1
10
100
0 0.2 0.4 0.6 0.8 1
Dos
e Ra
te
(nG
y·cm
2·Bq-
1·h-
1)
Depth (cm)
MCNP ICRU 56
0.1 mm
1.0 cm
0.1 mm 1 cm
21
Rational fit function X(D) = a + b/(D-c) where X(D) = red channel scanner response
Non-Linear Least Squares FitR2 = 0.9997 Radj
2 = 0.9996
1E+04
2E+04
2E+04
3E+04
3E+04
4E+04
4E+04
5E+04
0 500 1000
Red
Cha
nnel
Pix
el V
alue
(16
bit)
Dose (cGy)
Film Measurement Fit
AA
22
0.0E+005.0E-081.0E-071.5E-072.0E-072.5E-073.0E-073.5E-074.0E-074.5E-07
0 0.1 0.2 0.3 0.4 0.5 0.6Dos
e R
ate
(cG
y s-
1 B
q-1
)
Depth (cm)
MCNP Measurement
AA
23
Bare Source vs. Tipped Source at the Surface
0
0.5
1
-0.5 -0.3 -0.1 0.1 0.3 0.5Rel
aive
Dos
e
Length (cm)
Relative Surface Dose Profile: Bare Source vs. Tipped Source
Bare Source Tip and RodMCNP: Bare Source MCNP: Tip and Rod
Film Piece: A2; Max Dose: 481 cGy
Film Piece: A28; Max Dose: 258 cGy
BareSlightly narrower profileFaster dose administration
D = 4.30E-07 cGy/s/Bq5 Gy time: 0.52 mCi*minT(min) = 0.10 (min*mCi)*D(Gy)/A(mCi)
TippedSlightly wider profileSlower dose administration
D = 1.82E-07 cGy/s/Bq5 Gy time: 1.24 mCi*min
Bare Source Placed on Surface
Source, Tip, & Rod Placed on Surface
Max dose rate is weakly dependent of the number of sourcesRelatively large distance between sourcesRelatively close proximity to surfaceOne source does not contribute greatly to the area beneath neighboring sources
Multiple Sources Applied to the Surface with the CSBT Device
25
6 SourcesDose Rate: 8.78 cGy/s/mCiTime5Gy: 0.95 mCi*min
6 SourcesDose Rate: 7.76 cGy/s/mCiTime5Gy: 1.07 mCi*min
7 SourcesDose Rate: 8.42 cGy/s/mCiTime5Gy: 0.99 mCi*min
8 SourcesDose Rate: 8.50 cGy/s/mCiTime5Gy: 0.98 mCi*min
Bare Source vs. Tipped Source at the SurfaceBareD=9.8 Gy/min/mCi
T[min]=0.11min∙mCi
Gy ∗Dx [Gy]A [mCi]
TippedD=3.89Gy/min/mCi
T[min]=0.28min∙mCi
Gy ∗Dx [Gy]A [mCi]
00.10.20.30.40.50.60.70.80.9
1
-0.5 -0.3 -0.1 0.1 0.3 0.5
Rel
aive
Dos
e
Position (cm)
Measured: Bare Measured: Tipped
MC: Bare MC: TippedD(tipped) =40% D(bare)
FWHM ≈ 0.18 cm FWHM ≈ 0.23 cm