~(223)Raイメージングにおける異なるコリメータと エネルギーウインドウの設定が総合感度および 総合空間分解能に与える影響

摘要

放射性同位元素（radio isotope: RI)内用療法は，体内 に投与された放射性医薬品の標的組織への選択的集積 を利用して放射線照射を行う治療であり，同時に画像 診断(theranostics)も可能である.近年，去勢抵抗 性前立腺癌の骨転移を対象とした新たな治療法としてα線放出核種であるラジウム（~（223）Ra)を利用した塩化ラ ジウム（~（223）RaCl_2) (Xofigo®, Bayer Healthcare)を用い たRI内用療法が登場し，全生存期間の延長と骨関連 事象の発現遅延の効果が期待されている.本邦で も日本人に対する有効性と安全性も証明され2016年 3月に承認された.%Objective: The present study aimed to reveal the influence of combination of different collimators and energy windows on the planar sensitivity and the spatial resolution during experimental ~(223)Ra imaging, and to determine optimal imaging parameters. Methods: A vial type source containing ~(223)Ra solution (4.55 MBq / 5.6 ml) was placed in the air at 100 mm away from the collimator surface. Planar images were acquired with LEHR, LMEGP, ELEGP and MEGP collimators on two dual-head gamma cameras (Symoia intevo (Siemens) and Infinia 3 (GE)). We compared three energy window combinations:1)single window at 82 keV, 2) double window at 82+154 keV, 3) triple window at 82+154+270 keV. The energy spectrum, the sensitivity and the spatial resolution, such as full-width at half-maximum (FWHM) and full-width at tenth-maximum (FWTM), of each collimator were assessed. Results: Five energy spectra (at around 82,154, 270, 351 and 405 keV) were essentially observed among four collimators. The sensitivity was high for LEHR collimator, then ELEGP and LMEGP collimator was 3-4 fold, which is greater than MEGP collimator. The 82 keV energy window of four collimators has best spatial resolution. Moreover, the spatial resolution of the 82 keV energy window with LMEGP and ELEGP collimator was almost equal to that of the triple window with MEGP collimator. Conclusions: Optimal imaging parameters were single energy window using LMEGP or ELEGP, and then triple energy window using MEGP collimator.