Dosimetric dependencies on target geometry and size in radioiodine therapy for differentiated thyroid cancer.

Purpose Radioiodine therapy is used in most disease stages for differentiated thyroid cancer. Its success depends on several factors, such as lesion size, completeness of surgery, extent of metastasis and tumoural iodine avidity. We aimed to investigate the importance of non-spherical geometries and size of metastases and thyroid remnants for the absorbed dose delivered. Methods Absorbed doses and energy depositions from homogeneously distributed iodine-131 in clinically relevant geometries and sizes were calculated using Monte Carlo simulations with MCNP6. A total of 162 volumes with different sizes and geometries corresponding to spheres, and prolate or oblate spheroids were simulated. Results Oblate and prolate spheroids had worse radiation coverage compared to spheres for equal masses, up to a difference of 38% for the most eccentric oblate spheroids and smallest masses simulated (a micrometastasis of mass 0.005 g). The differences in coverage could be explained by different volume - to - surface - area ratios of the spheroids. The impact of size alone caused up to 71% lower absorbed doses per decay in a spherical target mass of 0.005 g compared to 50 g. Conclusions While the iodine avidity, and therefore the total amount of decays, is the predominant contributing factor to absorbed dose in radioiodine therapy, eccentric spheroids and small target sizes can receive substantially lower absorbed doses from the same administration of radioiodine.

Treatment and control of sarcoptic mange: evaluation of treatment of both the pigs and environment.

Pigs in a herd infected with Sarcoptes scabiei var suis were treated with 20% phosmet at a dose rate of 20 mg/kg body weight. In one of the groups the environment was also treated using 2% trichlorphon. Post-treatment clinical examination and parasitological evaluation of skin scrapings revealed complete recovery by the end of the second month after initial treatment with no evidence of reinfection for a period of five months.

Systemic activity of coumaphos, famphur, crufomate, ronnel, and phosmet given orally to hens for control of the northern fowl mite, Ornitbonyssus sulviarum (Canestrini and Fanzago).

Coumaphos (O-(3-chloro-4-methyl-2-oxo-2H-1-benzopyran-7-yl)O,O-diethyl phosphorothioate), famphur (O-[p-(dimethylsulfamoyl)phenyl] O,O-dimethyl phosphorothioate). crufomate (4-tert-butyl-2-chlorophenyl methyl methylphosphoramidate), ronnel (O,O-dimethyl O-(2,4,5-trichlorophenyl) phosphorothioate) and phosmet (O,O-dimethyl phosphorodithioate S-ester with N-(mercaptomethyl) phthalimide) were administered as systemic acaricides (either single or multiple oral doses or as feed additives) for control of the nortnern fowl mite, Ornithonyssus sylviarum (Canestrini and Fanzago), on caged White Leghorn hens. None of the treatments controlled the mites, but some hens were poisoned.

Evaluation of phosmet for the control of the common scabies mite on cattle.

Thirty-four young range cattle heavily infested with the common scabies mite, Psoroptes ovis, were dipped in phosmet (O,O-dimethyl phosphorodithioate S-ester with N-(mercaptomethyl)phthalimide) in 15 trials. All concentrations from 0.15% to 0.25% that were applied once failed in at least one trial, but all concentrations from 0.075% to 0.20% were successful in eradicating mites when used twice at 7- to 10-day intervals. One single dip tried at 0.30% also was successful. Uninfested yearlings were dipped in 0.30% phosmet without apparent intoxication, but 2-year-old cattle treated in a spray-dip machine at 0.40% active ingredient became depressed and stiff gaited.