Recommendation for reducing the crystalline lens exposure dose by reducing imaging field width in cone-beam computed tomography for image-guided radiation therapy: an anthropomorphic phantom study.

In cone-beam computed tomography (CBCT) for image-guided radiation therapy (IGRT) of the head, we evaluated the exposure dose reduction effect to the crystalline lens and position-matching accuracy by narrowing one side (X2) of the X-ray aperture (blade) in the X-direction. We defined the ocular surface dose of the head phantom as the crystalline lens exposure dose and measured using a radiophotoluminescence dosimeter (RPLD, GD-352 M) in the preset field (13.6 cm) and in each of the fields when blade X2 aperture was reduced in 0.5 cm increments from 10.0 to 5.0 cm. Auto-bone matching was performed on CBCT images acquired five times with blade X2 aperture set to 13.6 cm and 5.0 cm at each position when the head phantom was moved from - 5.0 to + 5.0 mm in 1.0 mm increment. The maximum reduction rate in the crystalline lens exposure dose was - 38.7% for the right lens and - 13.2% for the left lens when blade X2 aperture was 5.0 cm. The maximum difference in the amount of position correction between blade X2 aperture of 13.6 cm and 5.0 cm was 1 mm, and the accuracy of auto-bone matching was similar. In CBCT of the head, reduced blade X2 aperture is a useful technique for reducing the crystalline lens exposure dose while ensuring the accuracy of position matching.

Nuclear myocardial perfusion imaging with a cadmium-telluride semiconductor detector gamma camera in patients with acute myocardial infarction.

OBJECTIVE: Since myocardial perfusion imaging (MPI) with conventional sodium iodine (NaI) device has low spatial resolution, there have been some cases in which small structures such as non-transmural myocardial infarction could not be properly detected. The purpose of this study was to evaluate potential usefulness of cadmium-telluride (CdTe) semiconductor detector-based high spatial resolution gamma cameras in detecting myocardial infarction sites, especially non-transmural infarction. METHODS: A total of 38 patients (mean age ± SD: 64 ± 21 year) who were clinically diagnosed with acute myocardial infarction were included. Twenty-eight cases of them were with ST segment elevation myocardial infarction (STEMI) and 10 cases with non-ST segment elevation myocardial infarction (NSTEMI). In all patients, myocardial perfusion single photon emission computed tomography images were acquired with Infinia (NaI device) and R1-M (CdTe device), and the images were compared concerning the detectability of acute myocardial infarction sites. RESULTS: The detection rates of the myocardial infarction site in cases with STEMI were 100% both by NaI and CdTe images. In cases with NSTEMI, detection rate by NaI images was 50%, while that of CdTe images was 100% (p = 0.033). The summed rest score (SRS) value derived from CdTe images was significantly higher than that from NaI images in cases with STEMI [NaI images: 12 (7-18) versus CdTe images: 14 (9-20)] (p < 0.001). SRS derived from CdTe images was significantly higher than that derived from NaI images in cases with NSTEMI [NaI images: 2 (0-5) versus CdTe images: 6 (6-8)] (p = 0.006). CONCLUSIONS: These results indicate that MPI using CdTe-semiconductor device will provide a much more accurate assessment of acute myocardial infarction in comparison to current methods.