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TEPC for Boron Neutron<br />

Capture Therapy<br />

Hsiu-Wen Hsiao<br />

934534<br />

May 2, 2007


• Introductions<br />

- BNCT<br />

Outline<br />

- Mixed radiation field dosimetry<br />

• Materials and Methods<br />

- The dual counter microdosimteric technique<br />

- Gas-filled and Measurement system<br />

- <strong>Energy</strong> <strong>calibration</strong>s<br />

• Results<br />

• Future works


BNCT (Boron Neutron Capture Therapy)<br />

thermal<br />

neutron<br />

10 B 11B<br />

7 Li<br />

nucleus<br />

4 He nucleus<br />

(α particle)<br />

γ-ray


BNCT facilities operating in the world<br />

• FiR-1 reactor Finland<br />

• HFR Petten<br />

• R2-0 reactor at Studsvik Sweden<br />

• RA-6 reactor Argentina<br />

• KUR/JRR4 Japan<br />

• MITR-II research reactor USA<br />

• LCR-I Czech Republic<br />

THOR (Tsing-Hua Open-pool Reactor), Taiwan


Mixed radiation field dosimetry<br />

• Mixed field<br />

– Fast neutron<br />

– Epithermal neutron<br />

–Photon<br />

–Dfast n – recoil protons<br />

–Dthermal n – 14N(n,p) 14C –Dphoton – 1H(n,γ) 2H – from mixed field photon <br />

– 10B(n,α) 7 The Dual Counter Microdosimetric technique<br />

-- paired low-pressure TEPC<br />

Dn Li<br />

• Within patient<br />

–D BNC


Microdosimetric Parameters<br />

Lineal energy (y)<br />

<br />

d<br />

Medium<br />

ε<br />

y =<br />

<br />

(J/m, keV/μm)<br />

ε = energy imparted<br />

= mean chord length<br />

= 4V/A = (2/3)d


Materials and Methods


The dual counter<br />

microdosimetric technique<br />

• Paired low-pressure TEPC<br />

- Boron-loaded A-150 TE counter<br />

- Non Boron-loaded A-150 TE counter<br />

Diameter = 2.5 cm<br />

Wall = 2.5 mm<br />

A-150 plastic<br />

with/ without<br />

boron loaded<br />

• Spectrum Boron-loaded - Spectrum NonBoron-loaded<br />

Spectrum BNC<br />

D BNC


The appearances of TEPC<br />

Boron concentration<br />

of wall<br />

0 ppm<br />

50 ppm<br />

commercial


TEPC<br />

• Anode<br />

– Material:Copper/Beryllium (Cu 98% / Be 2%)<br />

– Diameter:0.025 mm<br />

0.046 mm<br />

• Wall<br />

– Material: A-150 TE plastic ( and B 2 O 3 )<br />

– Thickness:2.5 mm<br />

1.25 mm<br />

• Cavity<br />

– Diameter:2.5 cm<br />

1.25 cm


Gas-filled system at NSRRC<br />

Valves<br />

TEPCs<br />

Vacuum pump<br />

manometer<br />

A gas cylinder with<br />

propane-based TE gas


The TEPC measurement system<br />

Oscilloscope<br />

H.V.<br />

Amplifier<br />

preAmp<br />

TEPC<br />

MCA


Operating condition<br />

<strong>Energy</strong> <strong>calibration</strong><br />

THOR50c beam<br />

Flow chart<br />

Microdosimetry spectrum<br />

Dose analysis<br />

Gas pressure<br />

Operating voltage<br />

Proton edge<br />

Alpha edge<br />

Gamma ray field<br />

TE (0 ppm、commercial)<br />

TE+B (50 ppm)


Operating condition<br />

<strong>Energy</strong> <strong>calibration</strong><br />

THOR50c beam<br />

Flow chart<br />

Microdosimetry spectrum<br />

Dose analysis<br />

Gas pressure<br />

Operating voltage<br />

Proton edge<br />

Alpha edge<br />

Gamma ray field<br />

TE (0 ppm、commercial)<br />

TE+B (50 ppm)


Simulation of small volumes-1<br />

Δx t<br />

E t<br />

a cell<br />

(tissue)<br />

Δx g<br />

E g<br />

counter<br />

Propane-based<br />

TE gas<br />

55% C 3 H 8 ,<br />

39.6%CO 2 ,<br />

5.4%N 2<br />

(TEPC)


Simulation of small volumes-2<br />

E t<br />

Δx t<br />

(tissue)<br />

E g<br />

Δx g<br />

(TEPC)<br />

⎪<br />

⎪<br />

⎩<br />

⎪<br />

⎪<br />

⎨<br />

⎧<br />

ΔΧ<br />

⎟<br />

⎠<br />

⎞<br />

⎜<br />

⎝<br />

⎛<br />

=<br />

ΔΧ<br />

⎟<br />

⎠<br />

⎞<br />

⎜<br />

⎝<br />

⎛<br />

=<br />

g<br />

g<br />

g<br />

g<br />

t<br />

t<br />

t<br />

t<br />

dx<br />

dE<br />

1<br />

E<br />

dx<br />

dE<br />

1<br />

E<br />

ρ<br />

ρ<br />

ρ<br />

ρ<br />

g<br />

g<br />

g<br />

t<br />

t<br />

t<br />

dx<br />

dE<br />

1<br />

dx<br />

dE<br />

1<br />

ΔΧ<br />

⎟<br />

⎠<br />

⎞<br />

⎜<br />

⎝<br />

⎛<br />

=<br />

ΔΧ<br />

⎟<br />

⎠<br />

⎞<br />

⎜<br />

⎝<br />

⎛<br />

ρ<br />

ρ<br />

ρ<br />

ρ<br />

g<br />

g<br />

t<br />

t<br />

ΔΧ<br />

=<br />

ΔΧ ρ<br />

ρ<br />

g<br />

g<br />

g<br />

g<br />

t<br />

t<br />

t<br />

t<br />

T<br />

P<br />

ΔΧ<br />

ρ<br />

T<br />

P<br />

ΔΧ<br />

ρ =<br />

t<br />

t<br />

g<br />

g<br />

t<br />

g<br />

t<br />

g<br />

P<br />

T<br />

T<br />

ΔΧ<br />

ΔΧ<br />

ρ<br />

ρ<br />

P =


Simulation of small volumes-3<br />

ρ ΔΧ T<br />

P P<br />

t t g<br />

g =<br />

t<br />

ρg ΔΧg Tt<br />

ρ g = 1.826 x 10 -3 g/cm 3 at P t = 760 torr, T g = 293 o K<br />

ΔX t = 1 μm;ΔX g = 2.5 cm<br />

ρ t = 1 g/cm 3 ; T t = 310.5 o K<br />

1 0.0001 293<br />

Pg= × × × 760<br />

0.0018 2.5 310.5<br />

= 16.87 torr ~<br />

17 (torr)


Operating condition<br />

<strong>Energy</strong> <strong>calibration</strong><br />

THOR50c beam<br />

Flow chart<br />

Microdosimetry spectrum<br />

Dose analysis<br />

Gas pressure<br />

Operating voltage<br />

Internal alpha source<br />

Proton edge<br />

Alpha edge<br />

TE (0 ppm、commercial)<br />

TE+B (50 ppm)


Internal alpha source <strong>calibration</strong><br />

– commercial TEPC<br />

internal alpha source<br />

-- Cm-244


• Spectrum of alpha<br />

from ICRU Report 36<br />

Low -energy<br />

delta rays<br />

Calibrations<br />

128 (keV/μm)<br />

straggling<br />

y<br />

= ×<br />

h<br />

p<br />

y h<br />

p<br />

constant


Operating condition<br />

<strong>Energy</strong> <strong>calibration</strong><br />

THOR50c beam<br />

Flow chart<br />

Microdosimetry spectrum<br />

Dose analysis<br />

Gas pressure<br />

Operating voltage<br />

Internal alpha source<br />

Alpha edge<br />

Proton edge<br />

TE (0 ppm、commercial)<br />

TE+B (50 ppm)


<strong>Energy</strong> Calibration — alpha edge<br />

• Simulation:<br />

Boron<br />

~ 50 ppm<br />

Cell membrane<br />

B-10 drugs<br />

A-150 TE plastic<br />

Propane-based<br />

TE gas<br />

cytoplasm<br />

nucleus


<strong>Energy</strong> Calibration — alpha edge<br />

10 B (n,α) 7 Li<br />

10 B (n,α) 7 Li


counts<br />

<strong>Energy</strong> Calibration — alpha edge<br />

700<br />

600<br />

500<br />

400<br />

300<br />

200<br />

100<br />

1um<br />

0<br />

0.1 1 10 100 1000<br />

y (keV/um) 386 keV/μm<br />

counts<br />

6000<br />

5000<br />

4000<br />

3000<br />

2000<br />

1000<br />

6 um<br />

0<br />

0.1 1 10 100 1000<br />

y (keV/um) 216 keV/μm


Operating condition<br />

<strong>Energy</strong> <strong>calibration</strong><br />

THOR50c beam<br />

Flow chart<br />

Microdosimetry spectrum<br />

Dose analysis<br />

Gas pressure<br />

Operating voltage<br />

Internal alpha source<br />

Alpha edge<br />

Proton edge<br />

TE (0 ppm、commercial)<br />

TE+B (50 ppm)


<strong>Energy</strong> Calibration — proton edge<br />

• According to papers:<br />

Proton edge<br />

Simulated<br />

diameter<br />

(μm)<br />

Proton edge<br />

(keV/μm)<br />

1 6<br />

146 105


Operating condition<br />

<strong>Energy</strong> <strong>calibration</strong><br />

THOR50c beam<br />

Flow chart<br />

Microdosimetry spectrum<br />

Dose analysis<br />

Gas pressure<br />

Operating voltage<br />

Internal alpha source<br />

Alpha edge<br />

Proton edge<br />

TE (0 ppm、commercial)<br />

TE+B (50 ppm)


Measurements of spectrum<br />

• Epithermal neutron beam of THOR<br />

Dual counter<br />

(TE, TE+B)<br />

In air: at beam exit 7 cm<br />

In phantom<br />

Same depth but different air gap<br />

Different depths


Results


<strong>Energy</strong> Calibration —<br />

Internal alpha source<br />

• Commercial TEPC<br />

• Spectrum of <strong>calibration</strong> -- 1 μm<br />

counts<br />

200<br />

150<br />

100<br />

50<br />

0<br />

0 200 400 600 800 1000 1000<br />

channel (ch)<br />

1.8 hrs<br />

8 hrs<br />

Shift ~15 channels<br />

128 keV/μm


<strong>Energy</strong> Calibration —<br />

detector drift characteristics<br />

• The possible reasons are as follows,<br />

- Outgassing of the plastic<br />

- Temperature shift<br />

- The plastic absorbs some of the gas after it has<br />

been in the vacuum.<br />

improved by filling it and waiting for a<br />

few hours before using it.


<strong>Energy</strong> Calibration —<br />

Internal alpha source<br />

• Calibration curve for alpha edge shift :<br />

channel of alpha edge (ch)<br />

520<br />

polynomial fit:<br />

y = 499.77796 + 4.58089X - 0.22175X^2<br />

500<br />

0 2 4 6 8 10<br />

time interval after filling TE gas (hrs)


yf(y)<br />

0.5<br />

0.4<br />

0.3<br />

0.2<br />

0.1<br />

Spectrum of Pu-239 source<br />

• Commercial TEPC -- 6 μm<br />

• Measurement time = 2 hrs<br />

1H(n, γ)H2<br />

0.0<br />

0.1 1 10 100 1000<br />

y (keV/um)<br />

Pu-239 source<br />

Recoil proton<br />

yd(y)<br />

0.5<br />

0.4<br />

0.3<br />

0.2<br />

0.1<br />

Pu-239 source<br />

1H(n, γ)H2<br />

0.0<br />

0.1 1 10 100 1000<br />

y (keV/um)<br />

Recoil proton<br />

Proton edge<br />

105 keV/um


Future works


Future works<br />

Operating condition<br />

<strong>Energy</strong> <strong>calibration</strong><br />

THOR50c beam<br />

Microdosimetry spectrum<br />

Dose analysis<br />

Gas pressure<br />

Operating voltage<br />

Internal alpha source<br />

Alpha edge<br />

Proton edge<br />

TE (0 ppm、commercial)<br />

TE+B (50 ppm)


References<br />

C. S. Wuu et al., Microdosimetry for Boron Neutron<br />

Capture Therapy. Rad. Res. 130, 355-359, 1992.<br />

Hsiao-Jay Huang, Microdosimetry Study of Neutrons using the<br />

Tissue Equivalent Proportional Counter, NTHU. 2004.<br />

Anthony J. Waker, Miniature tissue-equivalent proportional<br />

counters for BNCT and BNCEFNT dosimetry, Med. Phy., Vol.<br />

28, No. 9, Sep. 2001.<br />

Srdoc, D. Experimental Technique of Measurement of<br />

Microscopic <strong>Energy</strong> Distribution in Irradiated Mater using<br />

Rossi Counters. Rad. Res. 43, 302-319, 1970.<br />

David Tattam and T. Derek Beynon, Use of low-pressure<br />

tissue equivalent proportional counters for the dosimetry of<br />

neutron beams used in BNCT and BNCEFNT, Med. Phy.,<br />

Vol. 27, No. 3, March 2000.


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