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Lung Dosimetry for Radioiodine Treatment Planning in the Case of Diffuse Lung Metastases

¹ Division of Nuclear Medicine, Russell H. Morgan Department of Radiology and Radiological Science, School of Medicine, Johns Hopkins University, Baltimore, Maryland; ² Division of Medical Imaging Physics, Russell H. Morgan Department of Radiology and Radiological Science, School of Medicine, Johns Hopkins University, Baltimore, Maryland; and ³ Division of Endocrinology and Metabolism, Department of Medicine, School of Medicine, Johns Hopkins University, Baltimore, Maryland

View larger version (90K): [in this window] [in a new window]   FIGURE 1.  Whole-body planar projection (anterior view) of radioactive iodine distribution 3 h (A), 26 h (B), and 146 h (C) after diagnostic administration of 37 MBq. A standard (18.5 MBq) was placed by the patient's right foot during scan. Stomach and bladder can be seen on 3-h scan. Activity is localized to both lungs and retained there 146 h after injection. Gray level intensity in part of left lung is weaker due to overlap of heart.

View larger version (38K): [in this window] [in a new window]   FIGURE 2.  Selected transverse (A) and coronal (B) CT images (obtained from CT portion of SPECT/CT study and, therefore, of low resolution) and corresponding maximum-intensity-projection (MIP) images of transverse (C) and coronal (D) SPECT slices are shown. Loci with strong activity uptake are indicated by arrows. MIP images were generated using the MIAU software package.

View larger version (29K): [in this window] [in a new window]   FIGURE 3.  (A) MIP slices of processed lung activity probability map obtained from corresponding SPECT study. Color bar indicates intensity for normalized activity probability. (B) Representative slice of lung density map obtained from 27-h SPECT/CT scan. Density map and activity probability maps are direct inputs for MCNP4b dose calculation. (C) ROIs of tumors in a representative transverse slice, generated by 3D-ID, are shown.

View larger version (37K): [in this window] [in a new window]   FIGURE 4.  MIP slices of absorbed doses in lungs after MCNP4b electron and photon transports. Sagittal (A), coronal (B), and transverse (C) views of dose rates (mGy/MBq-s) calculated for activity and density maps at 27 h after tracer administration. Color bar indicates intensity for absorbed dose per disintegration.

View larger version (11K): [in this window] [in a new window]   FIGURE 5.  (A) Absorbed dose–volume histogram corresponding to dose-rate images shown in Figure 4. Average absorbed dose rate per unit activity per voxel is 3.01 x 10–5 mGy/MBq-s (dashed line). (B) Relative errors after 10 million histories of electron transport are plotted against voxel energy deposited.

View larger version (20K): [in this window] [in a new window]   FIGURE 6.  MIP coronal slice images of segmented activity maps. Activity was evenly divided into 10 (A) and 5 (B) levels. (C) Dose–volume histograms calculated from segmented activity maps: 20 (solid line), 10 (dashed line), and 5 (dotted line) levels; horizontal lines depict mean absorbed doses per disintegration.