Evaluation of mandibular invasion by head and neck cancers using 99mTc-methylene diphosphonate or 99mTc-hydroxymethylene diphosphonate and 201Tl chloride dual isotope single photon emission computed tomography.

Whether a patient with head and neck cancer has mandibular invasion or not is important in determining the method of resection surgery. But, no modality is adequately reliable when used alone in the evaluation of mandibular invasion. Therefore, to more accurately diagnose mandibular invasion in head and neck cancer, we used a new modality, namely, 99mTc methylene diphosphonate (MDP) or 99mTc hydroxymethylene diphosphonate (HMDP) and 201Tl chloride dual isotope single photon emission computed tomography (Tc/Tl SPECT). The aim of this study is to disclose the usefulness of Tc/Tl SPECT in the assessment of mandibular invasion by head and neck cancers. 99mTc-MDP or -HMDP SPECT (Tc SPECT)s and 201Tl chloride SPECT (Tl SPECT)s were performed in 34 patients with suspected mandibular involvement of head and neck cancer. Thirty of 34 cases underwent both TcMTl SPECT and CT examination. Tc/Tl SPECT fusion images were obtained using the Automatic Registration Tool (ART, TOSHIBA, Japan) system. In the diagnosis of mandibular invasion on Tc/Tl SPECT fusion images, a problem was that the range of Tc and Tl uptake was changed by the condition of display used in the reconstruction and expression of the images. Then, prior to clinical evaluation, to reveal the most appropriate upper window level for display, a phantom study was performed. In a clinical study, the upper window level was set at 40 or 50%, which were verified to be the proper values in the preliminary study. The diagnostic accuracy obtained using Tc SPECT, TcMTl SPECT and CT was compared with the histopathological findings. Tc/Tl SPECT at 40 and 50% upper window level had higher specificity, accuracy, and positive predictive value (73.3%, 85.3%, 81.8%) than Tc SPECT alone (21.4%, 67.6%, 64.5%) and higher sensitivity and negative predictive value (94.7%, 91.7%) than CT (70.6%, 72.2%) for detecting mandibular invasion. Tc/Tl SPECT was a useful diagnostic procedure for the assessment of mandibular invasion by head and neck cancers.

[Investigation of radioactivity measurement of medical radioactive waste].

To explore the possibility of which medical radioactive wastes could be disposed as general wastes after keeping them a certain period of time and confirming that their radioactivity reach a background level (BGL), we made a survey of these wastes in several nuclear medicine facilities. The radioactive wastes were collected for one week, packed in a box according to its half-life, and measured its radioactivity by scintillation survey meter with time. Some wastes could reach a BGL within 10 times of half-life, but 19% of the short half-life group (group 1) including 99mTc and 123I, and 8% of the middle half-life group (group 2) including 67Ga, (111)In, and 201Tl did not reach a BGL within 20 times of half-life. A reason for delaying the time of reaching a BGL might be partially attributed to high initial radiation dose rate or heavy package weight. However, mixing with the nuclides of longer half-life was estimated to be the biggest factor affecting this result. When disposing medical radioactive wastes as general wastes, it is necessary to avoid mixing with radionuclide of longer half-life and confirm that it reaches a BGL by actual measurement.

[Usefulness of imaging posture using modified oblique view of the axilla (MOVA) for sentinel lymph node scintigraphy in patients with breast cancer].

Identification of the sentinel lymph nodes in patients with breast cancer is often hampered by high radioactivity from the injection site, since the distance between the injection site and regional lymph nodes is quite short in these patients. We investigated the usefulness of the modified oblique view of the axilla (MOVA) method introduced by Haigh et al., aiming at better discrimination of the target and higher resolution. Compared with the standard anterior view (SAV) of the supine position and conventional oblique view (COV) imaging, MOVA was able to obtain a longer distance between the injection site and axillary lymph nodes in 20 of 21 lymph nodes. MOVA provided more effective information for visual evaluation of the geometry of axillary lymph nodes in half the cases, and one lymph node was detected only with MOVA. In contrast, SAV provided better imaging in one patient. Although our results support the usefulness of MOVA, the combined application of MOVA and SAV is desirable, since sentinel lymph node detection with the gamma-probe is performed in the supine position during surgery.