Correlation between radiation dose, synovial thickness, and efficacy of radiosynoviorthesis

Objective. To correlate the therapeutic efficacy of radiosynoviorthesis (RS O) to radiation doses achieved. Methods. In 20 patients with known rheumatoid arthritis, radiosynoviorthesi s was performed in 36 joints. Arthritis disease activity was assessed by "b lood pool scintigraphy" (n = 29) score after injection of 370 MBq Tc-99m-MD P, before and at 1, 2, and 5 months after the RSO in 12 patients. For semiq uantitative measurements, a region-of-interest technique was applied. Synov ial thickness and response to the RSO were evaluated by joint ultrasonograp hy. Pain levels were evaluated semiquantitatively. Dosimetry (n = 20) was c alculated using planar quantification according to the MIRD scheme. Results, The mean radiation absorbed dose of Re-186-sulfate to the whole bo dy was 5.3 +/- 2.7 cGy, liver 10.0 +/- 8.1 cGy, spleen 20.3 +/- 22.9 cGy, k idneys 9.4 +/- 11.4 cGy, and at the injected joints of the shoulder 120.5 /- 32.2 Gy, hand 130.0 +/- 12.6 Gy, elbow 83.6 +/- 38.7 Gy, and talar/subta lar joint 84.1 +/- 30.7 Gy. In 7 cases, where mandatory immobilization of t he joint was not possible, the dose to the lymph nodes (n = 25) was 25.9 +/ - 53.8 Gy (maximum 189 Gy) and to single lymph nodes 14.6 +/- 11.2 Gy (maxi mum 63 Gy). The reduced doses to the synovia (at 40% leakage) were: Er-169- citrate 73.10 +/- 25.25 Gy; Y-90-citrate 59.25 +/- 46.45 Gy; Re-186-sulfate 65.40 +/- 32.55 Gy. In cases of complete immobilization, the dose to the l ymph nodes was negligible: Er-169-citrate (n = 7), whole body dose 0.4 cGy, lymph nodes 2.3 Gy, finger joints 132.3 +/- 34.3 Gy; Y-90-citrate (n = 6), whole body dose 15.5 cGy, Liver dose 26.5 cGy, splenic dose 11.9 cGy, kidn ey dose 67 cGy, joint knee joint dose 130.1 Gy. Regarding therapeutic effec t, mean reduction of the Tc-99m-MDP blood pool activity was 41% at first mo nth, 48% at second month, 48% at the fifth month, 48% in larger joints, and 63% in finger joints. Three and 6 months after RSO, sonography showed a me an reduction in synovial swelling: in the knee joint 1.67 and 4.38 mm, resp ectively; in the larger joints (shoulder, elbow, hand, talar/subtalar) 0.88 /1.93 mm; and in finger joints 0.53/1.76 mm. Clinically, best results were observed in the finger joints. Conclusion. 1. We observed a significantly higher radiation absorbed dose t o the lymph nodes and lower dose to the synovia in the absence of joint imm obilization. Immobilization of the joint is essential. 2. At 2 months after treatment, a significant reduction of blood pool activity and synovial swe lling was observed, with further improvement in the following months, espec ially in the finger joints. 3. There is a strong correlation between the re duction of blood pool activity, synovial swelling, and improvement of pain.