Targeted radiotherapy dosimetry of 153Sm hydroxide macroaggregates for radiation synovectomy

The dosimetry of the recently developed Sm-153 hydroxide macroaggregates (Sm-153- MH) for radiation synovectomy has been studied as an agent for the treatment of arthritic synovial joint diseases. This pharmaceutical formulation presents optimal properties in terms of particle size (average 4 pm) sedimentation (0.008 cm min(-1)) and biological behavior. Direct measurements of depth dose distributions for this beta-gamma emitter present a difficult task; therefore, calculations of depth dose profiles are an invaluable tool for investigating the effectiveness of this therapeutic technique. In spite of the importance of these calculations there are only a few studies dealing with the experimental validation of these calculated depth dose distributions. On the present work the Monte Carlo (MCNP4B) calculated beta-gamma depth dose profiles for a liquid Sm-153 beta-gamma source used in radiation synovectomy are compared with experimental depth dose distribution obtained using radiochromic dye film dosimetry (GafChromic(TM)), The calculated and experimental depth dose distribution showed a very good agreement (within 5 %) on the region where the dose deposition is dominated by the beta-particle component (first 800 microns depth on tissue equivalent material). The agreement worsens reaching a maximum deviation of 15 % at depths close to the maximum range of the beta-particles. Finally the agreement improves for the region where the gamma component accounts for one third of the total absorbed dose (depths >1 mm). The possible contributions to these differences are discussed as well as their relevance for the application of 153Sm for the treatment of rheumatoid arthritis.