INTERCOMPARISON OF PROTON DOSE WITH TLD
Takashi Nakamura, Toshiso Kosako
Institute for Nuclear Study, University of Tokyo
Akira Itoh
Institute for Medical Science, University ·of Tokyo
Akira Maruhashi
Department of Clinical Medicine, University of Tsukuba
This work has been done as one of the US-Japan co-operative cancer research
program. Four types of tissue equivalent thermoluminescent dosimeters of BeO,
6LiF,7LiF and Li2B40 7 :Mn were used to get the spatial absorbed dose distribution
in phantom irradiated by 52-MeV proton beam of FM cyclotron at Institute forNuclear Study, University of Tokyo. The sizes of TLDs were powders encapsuledin a 1.2-mm-diam. by 8-mm glass tube for BeO, 1 x 1 x 6 mm3 rods for 6LiF and7LiF and 3.2 x 3.2 x 0.9 mm3 ribbon for Li 2B407:Mn.
These TLDs were at first calibrated under the reference field of 6Gco gamma
source at Institute for Medical Science, University of Tokyo. The exposure dose
was 87.60 R/min and the absorbed dose was 84.84 tissue rad/min at 0.5cm depth
in phantom. The average values of responses per tissue dose for 60co gamma rays
were obtained as follows;
BeO
6LiFhiFLi2B 4o7 :Mn

2.566 ± 0.113
1.016 ± 0.026
1.144 ± 0.061
91.78 ± 4.62

tissue rad/rad in.TLD reader
IIIIII

These dosimeters were arranged at 6.35 mm depth in acrylic plastics of density 1.19 placed perpendicularly to the proton beam. The proton beam was monitored
The proton beam was.
by a Faraday cup connected to the current integrator.
formed to have as a flatter top as possible by observing the beam profile with themulti-wire proportional counter, and at the same time more precise structure ofbeam profile was measured horizontally and vertically by scanning silicon dosimeters of 1.4-mm-diam. by 0.22-mm-thick disk.
The measured tissue absorbed dose per beam monitor counts are tabulated in
Their values show good agreement each other with some
Table 1 for four TLDs.
The proton tissue dose clearly decreases with increasing the horidistortions.
zontal deviation of the TLD position from the beam center all for four TLDs,
This entrance dose distribution well corresponds toexcluding several values.
the horizontal proton beam profile measured with silicon dosimeter which is shownin Fig. 1, such as 70- 80% at 1 em and 85- 95% at 0.75 em of the dose at thecentral position of the beam.
The measured results are compared with those by tissue equivalent ionization
The TLD results show fairly good agreement withchamber of 1.3 em diam. (IC).
the IC results, but in general, the former gives higher dose values than theThis discrepancy can be explained from the following two facts:
latter.

-99-

~trance Dose 11 af the 52 Xel/ ?rot:on Beam

Table I1) TLDs were all placed behind
6.35 mm acrylic plastics andIC was behind 3 mm PPTEP
window.
2) The IC size is about 10 times
larger than the TLD sizes, sothe absorbed dose averaged in
IC becomes less than that inTLD, since the beam profile
has not a flat top as seen inFig. 1.

Dosimeter?rotan Tissue Dose(radlPOSl.tion

1/ert.

Horiz.
Ionization
Chaml:::lercmP

89.03

176.6

-o. 75cm ±0.4cm

106.3

238.6

-O.JS

115.2

266.5

.o.o

114.2

211.4.

l.J

BeO

210.7

0.35

196.3

0. 75

Ionizationl.J em."

88.41

176.1

96.68

175.6

-o.stoG. a

187.9

0.0

Ll3.i198.70 .s

98.90

197 .J

1.060. ao

139'.9="'38.53

175.9±0. J=:n92.98

177.9

-0.5

LOS .1

187.9

a. a

119.2

224 .J

Chamber
6 tiF-l.OcmThe authors wish to thankDr. T.Hasegawa and Messrs. I. Sugai
and K. Takaku for their kindful
cooperation during this experiment.
Ionization

l.J

Chamber
7r.i.F±O.J·cm-LOcm

24·2. 4

0.5

195.4

l.aranl..zac..ionl.J

Chamber

em ·P-o. 75~ -+-0.4C!I1

177 .l1755.6

194.72116."

0. 0204.]2492.40. 75

LSS .22.644. 7

204.4-·J. 4-O.JS~28.9

0. 35-J. 75

2111.90.0

2182.5Q. 75

2192.4l) T:::.O were d!l placed. benind 6.35 mm- acrylic ?lasc.l.cs and.... as benind J mm PP'l'EP. w~naow.

c~amberthe ionl.za.tl.an

21 The flOSl.tion ot TLD indicates the norizont:ai w.nd vertical.
devl.at:.l.Ons from the beam center.
jI' 'Vertlcal Beam Ptof1ie
IIii',III ii: l"orlI IiIIj]

ICl "~I.'IIIiI' II:\i\IIII
I
It!

I

I'
Fig. 1\;

J

I,!
I'!'''II•
I·• li

III'I
II,Ii

I

I:i

I I
I

I~

j

I !/'l·rtl~:,' TITil~~II

I, , , :j

I';I ~I.'
'!
i,,
i

I~!

17

I;

.I

Proton beam profile measured with silicon dosimeter-100-