Occupational radiation exposure in nuclear medicine presents complex spatial and temporal patterns due to the use of unsealed radiopharmaceuticals and prolonged proximity to patients. Traditional passive dosimetry provides only cumulative dose values, limiting its usefulness in identifying task-specific exposures or capturing momentary fluctuations. This study applied a real-time dosimetry system capable of second-by-second measurements, combined with time-series analysis, to evaluate staff exposure during myocardial perfusion imaging using technetium-99m. Dosimeters were placed on the left and right sides of the neck and head of two radiological technologists. Dose rates were continuously recorded throughout the injection and imaging phases. The right side of the neck received the highest cumulative and peak dose rates among all sites. Although no significant difference in total dose was observed between the injection and imaging phases, specific high-exposure events were detected. Notably, ECG lead placement and post-injection handling produced dose spikes. A positive correlation was found between administered activity and dose rate at neck-level sites but not at head-level sites. These findings demonstrate the value of real-time dosimetry in identifying procedural actions associated with elevated exposure. Time-series analysis further contextualized these peaks, supporting improved task-specific protective strategies beyond the capabilities of conventional dosimetry.

【目的】本研究の目的は，核医学（SPECT）における放射性医薬品の投与量を適正化することである．そこで，99mTc製剤を用いた安静時心筋シンチグラフィにおいて，体重を指標とした可変用量法（VD法）を検討した．【方法】本研究では，VD法と，体重による変動のない固定用量法（FD法）を比較した．対象はVD法50例，FD法50例とした．VD法については，SPECT 1 viewあたりの目標平均カウント（counts/pixel）を設定した．FD法における心筋平均カウントと検査開始時推定体内放射能量を用いて，体重によって適宜変動するVD法の投与量を算出した．【結果】VD法はFD法より心筋カウントのバラつきが少なく目標カウントに近くなり，投与量の中央値は減少した．【結語】VD法により安静心筋血流シンチグラフィにおいて，体格に依存しないカウントの取得と安定した画質の提供および医療・職業被曝低減の可能性が示唆された．