Evaluation of the scatter doses in the direction of the buccal mucosa from dental metals.

The presence of dental metals creates radiation dose perturbation due to scattered radiation during radiation therapy for the head and neck region. The purpose of our study was to compare the scatter doses resulting from various dental metals in the direction of the buccal mucosa among a single-field technique, three-dimensional conformal radiation therapy (3D CRT), and intensity-modulated radiation therapy (IMRT) during radiation therapy for the head and neck region. We used nine metal cubes with 10 mm sides, which were placed inside a water phantom. The scatter doses from the cubes in the direction of the buccal mucosa were measured using radiochromic films. The films were placed perpendicularly to the surface of the cubes. The phantom was irradiated with a 4 MV photon energy by a linear accelerator for all techniques. In the single-field technique, the scatter doses from dental metals showed 3.7%-19.3% dose increases, and gold showed the largest dose increase. In 3D CRT, the scatter doses from dental metals showed 1.4%-6.9% dose increases, which were within the measurement uncertainty (except for gold). In IMRT, the scatter doses from dental metals showed only 1.4%-4.3% dose increases, which were all within the measurement uncertainty. During radiation therapy for the head and neck region, the scatter doses from the tested dental metals in the direction of the buccal mucosa in 3D CRT or IMRT were lower than those using the single-field technique. However, there were no differences between the scatter doses resulting from particular dental metals in the direction of the buccal mucosa in 3D CRT and those in IMRT, except for gold.

Effect of metallic materials on magnetic resonance image uniformity: a quantitative experimental study.

OBJECTIVE: To assess quantitatively the effect of metallic materials on MR image uniformity using a standardized method. METHODS: Six types of 1 cm cubic metallic materials (i.e., Au, Ag, Al, Au-Ag-Pd alloy, Ti, and Co-Cr alloy) embedded in a glass phantom filled were examined and compared with no metal condition inserted as a reference. The phantom was scanned five times under each condition using a 1.5-T MR superconducting magnet scanner with an 8-channel phased-array brain coil and head and neck coil. For each examination, the phantom was scanned in three planes: axial, coronal, and sagittal using T1-weighted spin echo (SE) and gradient echo (GRE) sequences in accordance with the American Society for Testing and Materials (ASTM) F2119-07 standard. Image uniformity was assessed using the non-uniformity index (NUI), which was developed by the National Electrical Manufacturers Association (NEMA), as an appropriate standardized measure for investigating magnetic field uniformity. RESULTS: T1-GRE images with Co-Cr typically elicited the lowest uniformity, followed by T1-GRE images with Ti, while all other metallic materials did not affect image uniformity. In particular, T1-GRE images with Co-Cr showed significantly higher NUI values as far as 6.6 cm at maximum equivalent to 11 slices centering around it in comparison with the measurement uncertainty from images without metallic materials. CONCLUSION: We found that MR image uniformity was influenced by the scanning sequence and coil type when Co-Cr and Ti were present. It is assumed that the image non-uniformity in Co-Cr and Ti is caused by their high magnetic susceptibility.

Diffuse large B-cell lymphoma of the mandible with periosteal reaction: a case report.

This report describes a rare case of a 63-year-old man with a lymphoma in the right mandibular ramus with periosteal reaction. Computed tomography (CT) images showed a soft tissue density (28 × 48 × 32 mm) around the right mandibular foramen. Bone-mode CT images showed diffuse bone destruction of the right mandibular ramus. Moreover, a periosteal reaction was seen on the lingual cortical bone of the right mandibular ramus. Histopathologic examination found a diffuse large B-cell lymphoma.