Radiogold Seeds for 
Cancer Therapy 
RaDIOGOLD sEEDS and linear sources 
developed during the past three years 
(1-6) have displaced radon completely 
in radiation therapy at The Ohio State 
University Medical Center. These 
sources are now used advantageously 
in many types of cases in which radio- 
active cobalt was formerly applied 
(6-10). 
In external appearance the Au‘? 
seeds are indistinguishable from the 
usual radon seeds, and they can be 
utilized in the same manner and with 
the same apparatus. The half-life of 
Au!98 is 2.70 days, which is about 0.7 of 
the half-life of radon (3.83 days). 
The energy of the gamma radiation 
emitted by Au! is 411 kv; it is mono- 
energetic in contrast with the range of 
energies between 184 kv and 2,198 kv 
for the sdozen different gamma rays 
emitted by radon and its disintegra- 
tion products (11). Further biological 
studies (1, 2) are under way to deter- 
mine the relative merits of the differ- 
ences in half-lives and gamma-ray 
energies of Au!’ and radon. 
Sources for interstitial applications 
should not be confused with radioactive 
gold in the colloidal state which is now 
being used in some medical centers for 
the treatment of pleural and peritoneal 
carcinomatosis. In contrast to col- 
loidal Au!®’, in which the beta radiation 
emitted by the radiogold is used 
primarily, gold seeds containing Au!%* 
are employed only because of the 
gamma rays emitted from the radio- 
gold within them. The seeds are 
usually superior because of the rela- 
tively homogeneous dosage of ionizing 
radiation that may be achieved when 
discrete sources of gamma rays are 
properly spaced in accordance with 
well-established physical principles. 
Dosimetry is highly uncertain when- 
ever radioactive sources are injected 
that are mainly dependent on the emis- 
sion of beta particles for whatever 
effectiveness they may have. The 
Au! seeds are, therefore, essentially 
similar to radon seeds, where much of 
the beta radiation is removed by 
filtration. 
Advantages of Au!®* seeds over radon 
*Julius F. Stone Research Associate 
Professor of Medical Biophysics. 
seeds for applications in therapy 
include: 
1. Radiogold seeds of any strength 
can be cut instantly, even at the time 
the decision to use them is made (e.g. 
in the operating room), whereas radon 
seeds usually must be ordered a day or 
more in advance of the time they are 
to be used. 
2. Radiogold seeds are very uniform 
in strength, but wide variations in 
strengths are often found in radon 
seeds. 
3. Because gold is a metal there is 
no danger of leakage of gas from Au!%® 
seeds. 
4. The beta particles emitted by 
Au!8 with maximum energy of 970 kv 
are almost completely filtered out, in 
contrast to the beta particles emitted 
by radon disintegration products with 
maximum energy of 3,170 kv. 
5. The facilities and equipment re- 
quired for manufacturing seeds loaded 
with Au!’ are simple and inexpensive. 
6. Problems of protection are greatly 
simplified in the preparation and 
handling of Au!%* seeds because the 
half-value layer in lead for the gamma 
rays is only 2.8 mm, in contrast to 
14 mm for radon. 
Preparation of Sources 
Each Monday there arrives in 
Columbus via air express a package 
shipped by the Oak Ridge National 
Laboratory earlier that day. This 
package contains several pure gold 
wirest 0.2-0.3 mm in diameter and 
85 mm long that have been irradiated 
during the previous week in a flux of 
about 1-5 X 10" thermal neutrons/ 
cm?/sec in a nuclear reactor. In the 
radioisotope laboratory the radioactive 
wires are slid into inert gold tubingt 
about 0.4 mm inside and 0.8 mm out- 
side diameter. This nonradioactive 
outer gold tubing absorbs almost all 
of the beta particles and passes about 
90 % of the 411-kv gamma rays emitted 
by the radioactive gold wire contained 
within it. 
Seeds are cut to any desired strengths 
with a simple cutter. The device con- 
sists of a lead block with a central bore 
+ Supplied by the American Platinum 
Works, Newark, New Jersey. 
By ULRICH K. HENSCHKE, 
ARTHUR G. JAMES, and 
WILLIAM G. MYERS* 
Departments of Radiology, Surgery, and Medicine 
The Ohio State University Medical Center 
Columbus, Ohio 
into which the encased radioactive 
gold wire is introduced and from which 
it may be éxtruded to any desired 
length from 1 to 40 mm, preadjusted 
by a micrometer. The gamma radia- 
tion of the part of the encased radio- 
active gold wire pushed outside of the 
lead shield to be cut off with the cutter, 
is measured with a radiation survey 
meter equipped with an ionization 
chamber (‘‘Cutie-Pie”’ type). 
Calibration of seed strength. The 
survey meter is placed in a fixed posi- 
tion at such a distance from the cutter 
that a swing of the needle to 20 scale 
divisions on the 50 mr/hr full-scale 
range of the meter will result in a Au! 
seed which will deliver 1,000 gamma 
roentgens-total-at-one-centimeter 
(designated ‘“‘rtcm’’) during complete 
decay. This is approximately the 
same strength as the 1,112 r given off 
during lifetime decay of 1 me of radon 
enclosed in 0.5 mm. of platinum. The 
cutter is portable and is often taken 
to the operating room where Au!%8 
seeds are calibrated and cut in a few 
seconds 
Details of design of the cutter, of the 
method of calibration of the sources, 
and of dosimetry with the Au!*8 seeds 
will be published separately. 
Following publication (1, 2) of the 
method developed here for making 
sources containing Au!®, Sinclair (12) 
briefly described sources made from 
cylinders of gold sealed in a platinum 
beta-particle absorber before exposure 
to the neutron flux in a nuclear reactor. 
The method described here for pre- 
paring Au!’ seeds would appear to be 
a superior one in the following respects: 
1. The radiation therapist has all of 
the advantages of on-the-spot adjust- 
ability of strengths of sources provided 
by a radon plant without the many 
well-known disadvantages associated 
with the establishment and operation 
of a radon plant. The method de- 
scribed by Sinclair does not permit 
adjustment of strengths of sources 
at the point of usage, nor does it 
enable the therapist to compensate 
for decay of radioactivity by making 
longer seeds or by using successively 
thicker radioactive gold wires irradi- 
ated in the same container in the 
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