6.9. RADIOSYNOVECTOMY
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(a) The signed informed consent of the patient is obligatory.
(b) The patient should undergo ultrasound (arthrosonography, 7.5 MHz) or
MRI to evaluate the joint space as well as the structure of the synovia.
(c) A three phase bone (
99m
Tc-MDP) scintigraphy must be performed to
assess the degree of inflammation. Radiosynovectomy has been demon
-
strated to be successful only if a clear synovitis is indicated by three phase
bone scintigraphy, especially in patients with arthrosis (or arthrosis–
arthritis).
6.9.6. Radiopharmaceuticals
6.9.6.1. Colloids
Because of its deep tissue penetration,
90
Y-colloid is suitable for the knee
and in joints with greatly thickened synovium. For joints of intermediate size
(wrist, elbow, shoulder and hip)
186
Re-colloid has been successfully used and
for the smallest joints (phalanges)
169
Er-colloid.
Yttrium-90 has been bound to silicate, citrate and ferric hydroxide
compounds as colloids. Currently, it is most frequently used as
90
Y- ci tra te,
which ranges in particle size from 10 to 100 nm. Leakage estimates for
90
Y-
citrate range from 5 to 10% after 24 hours and from 15 to 25% after 4 days.
Extra-articular radiation absorbed doses for liver (2.7 mGy/MBq) and regional
lymph nodes are, therefore, quite high (270 mGy/MBq). Owing to its small
particle size, and thus higher leakage,
198
Au is no longer recommended.
6.9.6.2. Dysprosium-165 macroaggregates
In order to reduce leakage from the synovial space,
165
Dy-ferric
hydroxide macroaggregates have been applied for joint therapy. The particle
size averages 5 mm and the activity that does leak from the joint quickly decays
(with a half-life of
165
Dy of 139 min), thus reducing extraneous organ
irradiation.
6.9.7. Dose and route of administration
It is assumed that intra-articular colloids are uniformly distributed over
the joint surfaces. The most apparent problem is leakage from the joint space,
primarily by lymphatic clearance, which depends largely on particle size.
Leakage is reduced by a flushing injection of a long acting steroid (such as
prednisolone acetate) after radiopharmaceutical injection. Table 6.4 provides
an overview of the doses used successfully for radiosynovectomy.