Abstract
Purpose: A dosimetric characterization of IBt-Bebig iodine-125 interstitial seed, the first iodine seed in biocompatible polymer, recommended by AAPM (American Association of Physicists in Medicine) was carefully determined for medical applications by measurements and two independent Monte Carlo calculations. Methods: Measurements were obtained with LiF thermoluminescent dosimeters (1mm3 microcubes) in solid water phantoms (WT1). Measured data were then compared to Monte Carlo calculated data in solid water utilizing the MCNP5 code with using the standard photoatomic data library, mcplib04. Results: Four seeds were calibrated according to NIST 1999 standard to calculate the dose rate constant, Λ. A comparison of anisotropy function with previous studies of metallic seed in literature indicates a clear improvement in isotropy for studied seed especially near the seed axis (−40° < angle < 40°); for example, at 5° it has a value of about 92%, whereas for Amersham model 6702 is in the order of 59% . Therefore, the new seed is more isotropic and penetrating. The impact of fluorescence X-rays of 12 keV generated by marker on the dosimetry was evaluated. The lead X-rays at 12 keV contribute 8.7% of the dose at 0.1 cm and rapidly fall to 2.7% at 0.5 cm. Its contribution becomes negligible at 0.7 cm however; they are not excluded from NIST measurements. This will result an overestimation of dose rate constant about of 14%. Conclusions: Dosimetric characteristics, following TG43U1 formalism, are presented for a new iodine seed made with a biocompatible polymeric shell with internal centrally located leaded glass marker. Studied seed doesnˈt have a large anisotropy effect and the use of polymer shell may eliminate the artifacts that occur in traditional medical imaging due to the metallic shell. All these effects, when taken together, make this seed potentially useful source for permanent brachytherapy.
Published Version
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