monte carlo simulation and validation of a novel yttrium-90 source...

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

Presenter

Presentation Notes

ICRU 56 “Dosimetry of External Beta Rays for Radiation Protection”

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

Presenter

Presentation Notes


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

Presenter

Presentation Notes

ICRU 56 “Dosimetry of External Beta Rays for Radiation Protection” Error bars based on film calibration error

Bare Source vs. Tipped Source at the Surface

Bare SourceSlightly narrower profileFaster dose rate

TippedSlightly wider profileSlower dose rate

Presenter

Presentation Notes


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



D(tipped) =40% D(bare)

BareFWHM ≈ 0.18 cm

TippedFWHM ≈ 0.23 cm

Presenter

Presentation Notes


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


7 Sources

D = 5.05 Gy/min/mCi


8 Sources

D = 5.10 Gy/min/mCi


Max dose rate is weakly dependent on the number of sources.

Presenter

Presentation Notes

Max dose rate is weakly dependent of the number of sources Relatively large distance between sources Relatively close proximity to surface One source does not contribute greatly to the area beneath neighboring 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

Presenter

Presentation Notes


AA

23

Presenter

Presentation Notes


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

Presenter

Presentation Notes


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




Bare Source vs. Tipped Source at the SurfaceBareD=9.8 Gy/min/mCi



TippedD=3.89Gy/min/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

Presenter

Presentation Notes


monte carlo simulation and validation of a novel yttrium-90 source...

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