Breast metrics were examined and a number of parameters were defined which may be useful for breast modeling. The reported data may provide researchers with useful information for characterizing the breast for various imaging or dosimetry tasks.

The COBRA method is a fast and accurate method for BT filter characterization, which requires a simple experimental setup in a clinical environment. Because of the ease of data acquisition, multienergy scans can be acquired which allow characterization of the BT filter thickness.

Purpose An imaging facility with a diverse fleet of CT scanners faces considerable challenges when propagating CT protocols with consistent image quality and patient dose across scanner makes and models. While some protocol parameters can comfortably remain constant between scanners (e.g. kV, gantry rotation time, etc.), the automatic exposure control parameter, which selects the overall mA level during tube current modulation, is difficult to match between scanners, especially from different CT manufacturers. Method Objective methods for converting tube-current-modulation protocols between CT scanners were developed. Three CT scanners were investigated, a GE LightSpeed 16 scanner, a GE VCT scanner, and a Siemens Definition AS+ scanner. Translation of the automatic exposure control (AEC) parameters such as noise index or quality reference mAs across CT scanners was specifically investigated. A variable-diameter polymethyl methacrylate (PMMA) phantom was imaged on the three scanners using a range of AEC parameters for each scanner. The phantom consisted of 5 cylindrical sections with diameters of 13 cm, 16 cm, 20 cm, 25 cm, and 32 cm. The protocol translation scheme was based upon matching either the CTDIvol or image noise (in HU) between two different CT scanners. A series of analytical fit functions, corresponding to different patient sizes (phantom diameters) were developed from the measured CT data. These functions relate the AEC metric of the reference scanner, the GE LightSpeed 16 in this case, to the AEC metric of a secondary scanner. Results When translating protocols between different models of CT scanners (from the GE LightSpeed 16 reference scanner to the GE VCT system), the translation functions were linear. However, a power-law function was necessary to convert the AEC functions of the GE LightSpeed 16 reference scanner to the Siemens Definition AS+ secondary scanner, due to differences in the AEC functionality designed by these two companies. Conclusions Protocol translation based on quantitative metrics – volume computed tomography dose index or measured image noise is feasible. Protocol translation has a dependency on patient size, especially between the GE and Siemens’ systems. Translation schemes that preserve dose levels may not produce identical image quality.

As part of the EXPLORER total-body positron emission tomography (PET) project, we have designed and built a high-resolution, high-sensitivity PET/CT scanner, which is expected to have excellent performance for companion animal whole body and human brain imaging. The PET component has a ring diameter of 52 cm and an axial field of view of 48.3 cm. The detector modules are composed of arrays of lutetium (yttrium) oxyorthosilicate (LYSO) crystals of dimensions 2.76 × 2.76 × 18.1 mm 3 coupled to silicon photomultipliers (SiPMs) for read-out. The CT component is a 24 detector row CT scanner with a 50 kW x-ray tube. PET system time-offlight resolution was measured to be 409 ± 39 ps and average system energy resolution was 11.7% ± 1.5% at 511 keV. The NEMA NU2-2012 system sensitivity was found to be 52-54 kcps MBq −1. Spatial resolution was 2.6 mm at 10 mm from the center of the FOV and 2.0 mm rods were clearly resolved on a mini-Derenzo phantom. Peak noise-equivalent count (NEC) rate, using the NEMA NU 2-2012 phantom, was measured to be 314 kcps at 9.2 kBq cc −1. The CT scanner passed the technical components of the American College of Radiology (ACR) accreditation tests. We have also performed scans of a Hoffman brain phantom and we show images from the first canine patient imaged on this device.

Purpose To demonstrate the feasibility of a dedicated breast computed tomography (bCT) platform to deliver rotational kilovoltage external beam radiation therapy (kVEBRT) for partial breast irradiation (PBI), whole breast irradiation (WBI) and dose painting. Methods and Materials Rotational kV-EBRT using the geometry of a prototype bCT platform was evaluated via Monte Carlo simulator. A point source emitting 178 keV photons (approximating a 320 kVp spectrum with 4 mm copper filtration) was rotated around a 14 cm voxelized polyethylene disk (0.1 cm tall) or cylinder (9 cm tall) to simulate primary and primary plus scattered photon interactions, respectively. Simulations were also performed using voxelized bCT patient images. Beam collimation was varied in the x-y plane (1–14 cm) and in the z-direction (0.1–10 cm). Dose painting for multiple foci, line and ring distributions was demonstrated using multiple rotations with varying beam collimation. Simulations using the scanner’s native hardware (120 kVp filtered by 0.2 mm copper) were validated experimentally. Results As the x-y collimator was narrowed, the 2D dose profiles shifted from a cupped profile with high edge dose to an increasingly peaked central dose distribution with sharp dose fall-off. Using a 1 cm beam, the cylinder edge dose was less than 7% of dose deposition at the cylinder center. Simulations using 120 kVp x-rays showed distributions similar to experimental measurements. A homogeneous dose distribution (< 2.5% dose fluctuation) with a 20% decrease in dose deposition at the cylinder edge (i.e. skin sparing) was demonstrated by weighted summation of four dose profiles using different collimation widths. Simulations using patient bCT images demonstrated the potential for treatment planning and image-guided radiation therapy (IGRT). Conclusions Rotational kV-EBRT for PBI, dose painting, and WBI with skin sparing is feasible on a bCT platform with the potential for high-resolution IGRT.