injection with sufficient technique is mandatory. An unacceptably high rate of serious complications including severe necrosis was reported after the injection of Y-90 into an ankle joint, which should be treated with a radionuclide of lower energy and a lower tissue range such as Re-186 [12]. In cases of radionecrosis or para-articular injection, no reliable recommendations exist owing to limited experience. One alternative would be to wait and watch carefully until demarked necrotic tissue can be resected. Another alternative would be to perform surgery immediately to remove as much of the para-injected activity as possible by flushing the tissue and by resecting radioactive tissue around the injection site [13].
cause both focal clustering of chondrocytes and fibrillation of the collagenous matrix of the articular cartilage [19]. Similar results with focal damage of chondrocytes and surrounding extracellular matrix were observed in eight patients with rheumatoid arthritis after treatment of the knee joint with 185 MBq of Y-90 [21]. Contradictory results with no microscopic signs of cartilage degeneration were found after the application of 150 MBq of Y-90 into the knee joints of dogs [20]. Although not as large as that to cartilage, the absorbed dose to bone surface and red bone marrow is also of interest in radiosynovectomy. The bone surface dose was described as being 25% of the synovial surface dose in the case of Y-90, down to 4% in the case of Re-186, and negligible for Er-169 [22]. The dose to the bone surface further decreases through the thickening of the synovial membrane in hemophilic synovitis. For the bone surface, a maximum dose of 18 Gy was calculated for 185 MBq of Y-90, which is not considered to be a dose sufficient to cause significant bone damage or necrosis. When there are already bony changes manifested on X-rays, it is better to avoid the procedure considering both its efficacy and safety. The dose to the bone marrow in large or mid-sized joints is considered negligible because the distance to the radiation source is greater than the mean tissue penetration of radionuclides used for radiosynovectomy.
A distribution scan acquired with a gamma camera after radionuclide injection is also helpful to verify successful intra-articular injection and proper distribution within the joint. KavaklÄą et al [14, 15] reported their experience of radiosynovectomy with Re-186 and Y-90 in two large series. As they observed no serious adverse events, they conclude that Y-90 for the knee joint and Re-186 for mid-sized joints are safe agents.
Radiation effects to articular cartilage and bone There is a potential risk of irradiation of healthy intra- and extra-articular tissues such as cartilage and bone from the radioactivity within the injected joint. Beta-emitting colloidal particles are phagocytosed by inflamed hypertrophic synovial tissue, including that part of the synovial lining that lies adjacent to the hyaline cartilage at its margins. Some irradiation of cartilage and subchondral bone during radiosynovectomy is thus inevitable. Although mature cartilage has been considered to be resistant to radioactivity, minor injury to articular cartilage remains a concern for radiosynovectomy especially in the pediatric population. Some studies using P-32 or Y-90 for radiosynovectomy reported injuries of both articular cartilage and the growth plate [16, 17]. Additionally, synovial damage, subsequent joint inflammation, and fibrosis may also contribute to articular cartilage damage after radiosynovectomy. Extensive fibrosis of the subsynovial tissues has been reported after radiosynovectomy with Y-90, Dy-165 ferric hydroxide macroaggregate, or P-32 [18–20]. Fibrosis may hamper filtration and resorption of synovial fluid, and lead indirectly to articular cartilage damage [13].
Whole-body radiation exposure Whole-body radiation-absorbed doses were reported ranging from 9 to 99 mSv after the application of 200 MBq of Y-90 into the knee joint with a median of 37 mSv [23]. In the same study, the total gonadal dose was 0.1 mSv in women and 0.2 mSv in men. van der Zant et al [24] calculated the effective dose for 75 MBq of Re-186 as 0.15 mSv using tissue weight factors defined by the International Commission on Radiological Protection. In another dosimetric study, Manil et al [25] calculated the effective dose for 70 MBq of Re-186 as 26 mGy. It might be possible that this calculation greatly overestimated the dose to the whole body, because the authors nevertheless concluded that their results were within certain methodological limitations. The primary disadvantage for radiation exposure in radiosynovectomy is the leakage of injected radioactivity away from the joint. The absorbed dose of regional lymph nodes may occasionally be quite large. After radiation synovectomy with Re-186, the activity in lymph nodes was reported to be up to 6% of the injected activity [25]. van der Zant et al [24] showed that, 24 h after radiosynovectomy with Re-186 in the ankle joints, the maximal leakage of the radioisotope to a single lymph node and the liver was 4% and 5.5% respectively. We have found that mean proportions of
According to experimental data and morphological in vitro studies, a radiogenic decrease in collagen synthesis must be taken into account if potential sideeffects of radiation synovectomy are discussed. However, because similar effects can be observed in hemophilic arthritis as well, the clinical impact of these findings is not clear. Intra-articular injection of 15 MBq of Y-90 in rabbit knee joints was reported to www.slm-hematology.com
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JCD 2009; 1:(1). OCTOBER 2009