Læknablaðið : fylgirit - 01.05.1978, Page 88

A. Rekonen,
Central Hospital,
Jyvaskyla, Finland.
RADIOPHYSICAL
CHARACTERISTICS
OF 90Y AND 169ER
Radioactive colloids have been used over ten
years in the local treatment of inflamed joints
in rheumatoid arthritis. During these years
radiation synovectomy as the treatment is called
has gained in many centers an accepted position
as an effective altemative besides the other
synovectomy forms.
Originally the amount of radioactivity used
intracavitarily was based mainly on clinical
experience. Presently, however, the physical
characteristics and other dosimetric factors are
taken into account in planning the intracavitary
treatment. I will now shortly present the main
characteristics of the radionuclides 9°Y which is
used in knee joints and 169ER which's use is
limited in small finger joints.
The radiation response in tissue is influenced
by two groups of factors: biological and physical
factors. Both can be divided in different items.
About the physical characteristic the most inport-
ant are: radiation characteristicsof the radionuc-
lide, time factors (retention) and geometry of
the joint cavity. The radiation response should
be evaluated in all tissues concerned, by
synovium and cartilage, lymph nodes, whole body
and periarticular tissue.
The first slide shows the radiation character-
istics of 90y_ Half time is 2.7 days, maximal
beta radiation mergy 2.27 MeV and half value
layer 1.0 mm. The half value layer means the
tissue depth which absorbs 507o of the radiation.
Lower part of the figure shows the decay scheme
Ii/2= 2.7d
Eyg (max) = 2.27 MeV
Efl (mean) = 0.97 MeV
di/2 = I.Omm
YTTRIUM SILICATE
particle size -100nm
90 Y 64 h
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