1. RADIOPARTICLES FOR RADIOSINOVECTOMY
María Graciela Argüelles
Centro Atómico Ezeiza,
Comisión Nacional de Energía Atómica
Buenos Aires, República Argentina

2. Rheumatoid arthritis
It is an ubiquitous incapacitating disease that places substantial demands on health care resources.
It affects 1% to 2% of the population worldwide, with a woman -to- man prevalence ratio of 3:1.
The characteristic disease manifestations of RA are joint pain, swelling and reduced mobility as a result of the synovial tissue inflammation,

3. Rheumatoid arthritis
any synovial joint in the body can be affected by the disease.

4. Rheumatoid arthritis
Pannus can be considered the most destructive element affecting joints in the patient with rheumatoid arthritis. It can attack articular cartilage and destroy it.

5. Radiosynovectomy
It consists of intra-articular injection of beta-emitting radionuclide in colloidal or particulate form, which comes into contact with synovium. Phagocytic cells absorb some of the injected dose, which is transmitted to the synovium.
If the amount of radioactivity injected is large enough the tissue will be destroyed. Regenerated tissue will be asymptomatic for 2-5 years.
Compared with surgical synovectomy, the radiation therapy is simpler and less traumatic, hospitalization time is shorter; cost is lower and duration of relief is comparable.

6. RADIONUCLIDE Ideal radionuclide
Pure beta-emitter or beta emitter with minimal gamma emissions.
5 mm < Tissue penetration < 10 mm
Short half-life
Low cost
Chemically pure
Non-toxic

7. Radionuclides Used for Radiation Synovectomy
Half life[days]
max. -energy [MeV]
tissue penetration depth [mm]
-energy [keV]
Dy-165
0,1
1,29
5,7 95
Re-188
0,7
2,12 / 1,96
11,0
155
Ho-166
1,2
1,85 / 1,77
8,5 81
Sm-153
1,9
0,67 / 0,81
2,5
103
Au-198
2,7
0,96
3,6
411
Y-90
2,28 -
Re-186
3,7
1,07 / 0,93
137
Lu-177
6,7
0,48
1,7
208
Er-169
9,4
0,34 / 0,35
1,0
P-32 14
1,71
7,9

8. Ideal particulate carrier
It must be taken up by synovial tissue.
It must form a stable complex with radionuclide.
It must be prepared easily and reproducibly.
Non-toxic.
Non- allergenic.

9. Finally, any biologically induced degradation of the agent should ideally release the radionuclide in a chemical form that rapidly egresses from the body.

10. Radionuclides production
Experimental
Radionuclides production

11. SAMARIUM-153 PRODUCTION Target material 152Sm (98.7 %) nitrate
Thermal neutron flux
Irradiation time
Specific activity
152Sm (98.7 %) nitrate
n/cm2s
36 hours
5-10 Gbq/mg

12. HOLMIUM-166 PRODUCTION Target material Thermal neutron flux
Irradiation time
Specific activity
165Ho (100 %) nitrate
n/cm2s
20 hours
4-5 Gbq/mg

13. Nuclear purity control
Multichannel analyzer with HPGe detector.
Gamma ray spectrum was identical to published nuclear data.

14. PARTICLES PREPARATION
Albumin microspheres
The microspheres were obtained by heat denaturalization of a human serum albumin (HSA) emulsion in vegetable oil. A 10 % human albumin solution and olive oil were used.
The HSA solution was added, drop by drop, into the olive oil stirring vigorously.
The emulsion was heated up to °C for one hour.
The suspension was cooled and diluted with n-hexane. It was filtrated with mesh 200 in order to discard the particles over 75 µm. The supernatant was filtered thorough membrane filter.
The microspheres were rinsed with acetone and dried.

15. Particles size measurement
It was performed using a optical microscope with micrometric ocular.

16. Size Distribution Of Microspheres

17. Electronic microscopy photographies

18. Hydroxyapatite particles
Ca(NO3) (NH4)2HPO4
A voluminous precipitate was formed. It was allowed to settle and the supernatant solution was discharged.
pH 12

19. Hydroxyapatite particles
The precipitate was rinsed with hot water, dried at 150 °C and heated for an hour at 240 °C to remove the ammonium nitrate. By strong heating at 800 °C for an hour, the product becomes largely anhydrous and hardened. The synthesis yield was always greater than 80%.

20. Size Distribution Of HA Microparticles

21. Labelling with 153Sm Labelling was done in two steps:
153Sm-citrate was prepared by adding sufficient citric acid to the 153SmCl3 solution to give a concentration of 15 mg/ml citric acid in 0,1 N HCl.
The radioactive solution was added to the particulate suspension (20 mg) stirring continuously (30 min, 37 °C).
Radiolabelled particles were rinsed with saline and separated by centrifugation (5 min at 1000 rpm) and labelling efficiency was determined.
The microspheres were resuspended in 2 ml of saline.

22. Labelling efficiency
The radioactive mixture was transferred to a centrifuge tube using 4 ml of saline to rinse, centrifuged at 1000 rpm for 5 minutes. The supernatant was then transferred to another tube. Measurements of radioactivity were made and labelling efficiency was calculated as percentage of initial activity.

23. In vitro stability
Stability of the labelled particles was studied in normal saline and 1% albumin solution, at 36°C over 48 hours. Albumin microspheres retained less than 80% of the initial activity after 48 h incubation.
HA particles retained radiactivity for 6 days.
EXTRA-ARTICULAR LEAKAGE
3 days
n = 6
6 days
Cumulative Leakage *
153Sm-HA
153Sm-citrate
* Blood, liver, kidneys, lungs, bone, urine.

24. PLA particles HoCl3 Acetylacetone Complex Ho(AcAc)3 pH 7
Evaporation Technique
Complex + PLA
Microsparticles
X-ray fluorescence and energy dispersive spectrometry were used to determine the presence of Ho in the particles and complex stoichiometry.

25. PLA particles
The particle size distribution of microspheres was determined by electronic microscopy.
Its diameter range was 20 µm.

26. HOLMIUM-166 FERRIC HYDROXIDE MACROAGGREGATES
166HoCl3 solution FeSO4solution
Coprecipitation 166Ho(OH)3 / Fe(OH)3
Macroaggregates were washed twice with PVP solution.
Particles were resuspended in saline and sterilized.
Obtention Efficiency > 90 %.

27. Quality control Radiochemical purity: ITLC / SG – EDTA Rf Ho3+ : 1.0
Rf particles : 0.0
Size:
light microscopy
serial filtration
In vitro stability:
Saline
EDTA solution
Pharmacological control :
Toxicity
Sterility
Pyrogenicity

28. Animal model - Normal New Zealand Rabbits
- Rabbits with antigen-induced arthritis
0 weeks: intradermic injection of ovoalbumin
3 weeks: intradermic injection of ovoalbumin

29. Animal model 6 weeks: intra-articular injection of ovoalbumin
7 weeks : synovitis symptoms
Intra-articular injection of 166Ho-FHMA
Gamma camera imaging

30. Gamma camera images
4 h p.i.
Zoom Zoom 4.0

31. Gamma camera images
24 h p.i.
Marker 99mTc Zoom Body scan