RADIOISOTOPES

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Incremental measurement technique of accumulated dose is required to evaluate radiation damage and to estimate residual-life of apparatus and materials used in radiation environment in nuclear power facilities.
Alanine/ESR dosimetry is well-known as a reliable dosimetry method and has suitable properties to apply to this field, such as wide useful dose range, long-term stability, and non-destructive readout.
In this work, feasibility of accumulated dose measurement under simulated condition was studied by irradiation up to 0.1 and 1 kGy at dose rates of 0.45 and 1.97 Gy/h and at elevated temperatures in the range of 25°C to 80°C. Long-term stability of dose response after irradiation was also studied at elevated temperatures during irradiation and storage.
Dose response of alanine dosimeter increases linearly up to 1 kGy at irradiation temperatures below 60°C, even when dosimeter was irradiated at a dose rate of 0.45Gy/h and for irradiation time up to about 2000 h. Alanine dosimetry allows us to measure accumulated dose without any correction at the above dose rate and temperature range.
Dose response depends on irradiation temperature, and linear dependence with a temperature coefficient of +0.1%/ °C was found for a dose of 0.1 kGy at dose rates of 0.45 and 1.97 Gy/h, although non-linear relation was found for dose of 1 kGy at a dose rate of 0.45Gy/h which is long irradiation time of about 2000h. Change in dose response after the end of irradiation is independent of dose rates, although it increases with dose and with temperatures during storage especially at above 60°C

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Rhenium-186 (¹⁸⁶Re) -labeled 1-hydroxyethylidene-1, 1-diphosphonate (HEDP) is reported to be effective for palliation of painful osseous metastases. Since a trial production of 186Re has begun at the Japan Atomic Energy Research Institute (JAERI), optimal conditions for 186Re-HEDP synthesis were investigated. Biodistribution of radioactivity after injection of 186Re-HEDP into mice was compared with that of ^99mTc-HEDP and ^99mTc-HMDP (1-hydroxyethylidene-1, 1-diphosphonate) . After pursuing parameters that affect radiochemical yields of ¹⁸⁶Re-HEDP, an instant HEDP-Sn kit was developed. This HEDP-Sn kit produced ¹⁸⁶Re-HEDP with high radiochemical yields and incorporated ¹⁸⁶Re radioactivity effective for palliation of osseous pain at safe HEDP levels. When injected into mice, ¹⁸⁶Re-HEDP demonstrated radioactivity localization in bone comparable to that of ^99mTc-HEDP and ^99mTc-HMDP. These findings imply that ¹⁸⁶Re-HEDP using ¹⁸⁶Re supplied from JAERI may have palliation effects similar to those hitherto reported. However, slower complexation rate and lower in vivo stability of ¹⁸⁶Re-HEDP than those of ^99mTc-HEDP calls for novel diphosphonate ligands based on the chemistry of rhenium.

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Three-detector scintillation camera has been widely used for the single photon emission computed tomography (SPELT) .
On this study, the three-detector camera was applied to whole body bone scintigraphy, and efficacy of this camera was evaluated in comparison with a single detector camera.
A set of posterior, left anterior and right anterior view was acquired in a single scanning.
Demonstrability of bone lesions by this set of image was compared with planar images by a single detector camera.
Bone lesions were more clearly demonstrated by the three detectors camera.
This result suggests that the three detectors camera is useful for the whole body bone scintigraphy as well as SPECT.

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