Radiopharmaceuticals

Searching for the ideal compound, a large number of different radiopharmaceu-ticals has been used since the beginning of radiation synovectomy (14). The energy of the ¡ particles must be high enough to penetrate the whole depth of the inflamed synovial membrane while both the adjacent articular cartilage and subchondral bone as well as the overlying tissue should not be damaged. This prerequisite makes clear that owing to the large range of joint size there will be no single radionuclide suitable for all joints. Related to joint size, three radio-nuclides have gained widespread acceptance for radiosynoviorthesis in Europe (15): yttrium-90 (Y-90), rhenium-186 (Re-186), and erbium-169 (Er-169). Dysprosium-165 (Dy-165) plays an important role in radiation synovectomy of knee joints in Australia. However, the short physical half-life of 2.3 hours for Dy-165, which is favorable for the radiation dose to the patient, is a disadvantage in timing the delivery from the manufacturer to the patient, which hampers a broader use. Phosphorus-32 (P-32) is mainly used for radiation synovectomy in

Table 1 Radionuclides Used in Radiation Synovectomy and Their Physical Properties

Maximum Gamma Half-life beta energy energy Maximum Mean range

Table 1 Radionuclides Used in Radiation Synovectomy and Their Physical Properties

Maximum Gamma Half-life beta energy energy Maximum Mean range

Radionuclide

(d)

(MeV)

(keV)

range (mm)

(mm)

Compound

Yttrium-90

2.7

2.27

11

3.6

Silicate,

citrate

Rhenium-186

3.7

1.07

137

3.7

1.1

Sulphide

Erbium-169

9.4

0.34

1.0

0.3

Citrate

Phosphorus-32

14.4

1.71

7.9

2.6

Chromic

phosphate

Dysprosium-165

0.1

1.29

95

5.7

1.3

Ferric

hydroxide hydroxide the United States. A summary of commercially available and routinely applied radionuclides for radiosynoviorthesis is given in Table 1.

Owing to its maximum tissue penetration of 11 mm, Y-90 should be used only for the treatment of knee joints. In all other joints there is a high risk of severe damage to the articular cartilage and necrosis of the overlying tissue. Re-186 is the candidate for treatment of mid-size joints while Er-169 is

Table 2 Radiopharmaceuticals and Recommended Activities for Radiosynoviorthesis

Radionuclide

Joint

Activity (MBq)

Yttrium-90

Knee

185-222

Rhenium-186

Shoulder

74-185 (111)

Elbow

74-111

Wrist

74

Hip

111-185

Ankle

74

Subtalar

37-74

Erbium-169

Thumb base

30-40

MCP/MTP

25-40

Proximal interphalangeal

20

Distal interphalangeal

10-15

Phosphorus-32

Knee

37-185

Ankle, shoulder, elbow

18-92

Wrist

Dysprosium-165

Knee, hip

10,000-11,000

Ankle

7400-9200

Activities given in bold are standard activities as used by the author. Abbreviations: MCP, metacarpophalangeal; MTP, metatarsophalangeal.

Activities given in bold are standard activities as used by the author. Abbreviations: MCP, metacarpophalangeal; MTP, metatarsophalangeal.

used for all finger and toe joints, and, more recently, for the temporomandibular joint as well as the iliosacral joint. P-32 and Dy-165, their ¡3 energy ranging between the energy of Y-90 and Re-186, are usually applied in knee joints and mid-size joints such as shoulder, elbow, wrist, hip, and ankle. Recommended activities and radiopharmaceuticals for the various joints are summarized in Table 2.

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