EBT and EBT2 film sensitivity showed strong energy dependence over an energy range of 25 keV-4 MV, although this dependence becomes weaker for larger doses. EBT3 film shows weak energy dependence, indicating that it would be a better dosimeter for kV x-ray beams where beam hardening effects can result in large changes in the effective energy.

This paper summarizes clinical commissioning of the world's first commercial, clinically utilized installation of a compact, image‐guided, pencil‐beam scanning, intensity‐modulated proton therapy system, the IBA Proteus® ONE, at the Willis‐Knighton Cancer Center (WKCC) in Shreveport, LA. The Proteus® ONE is a single‐room, compact‐gantry system employing a cyclotron‐generated proton beam with image guidance via cone‐beam CT as well as stereoscopic orthogonal and oblique planar kV imaging. Coupling 220° of gantry rotation with a 6D robotic couch capable of in plane patient rotations of over 180° degrees allows for 360° of treatment access. Along with general machine characterization, system commissioning required: (a) characterization and calibration of the proton beam, (b) treatment planning system commissioning including CT‐to‐density curve determination, (c) image guidance system commissioning, and (d) safety verification (interlocks and radiation survey). System readiness for patient treatment was validated by irradiating calibration TLDs as well as prostate, head, and lung phantoms from the Imaging and Radiation Oncology Core (IROC), Houston. These results confirmed safe and accurate machine functionality suitable for patient treatment. WKCC also successfully completed an on‐site dosimetry review by an independent team of IROC physicists that corroborated accurate Proteus® ONE dosimetry.

Hyperpolarized 3 He images of mouse lung are presented. Ventilation images and measurements of 3 He apparent diffusion coefficient (ADC) are reported in healthy mice, and preliminary studies of emphysema and lung cancer in mice are described using these techniques. The design and operation of an electronically controlled small-animal ventilator to deliver the hyperpolarized gas and control animal respiration are described. Images are acquired using an asymmetric gradient echo imaging method to enhance the signal-to-noise ratio of the rapidly diffusing 3 He. In mice with elastase-induced emphysema, the whole-lung average ADC is greater by approximately 25%, a statistically significant difference, compared to healthy animals. By contrast, mice exposed to cigarette smoke for up to 12 months reveal no statistically relevant increases in ADC, although emphysema was not confirmed in these mice. Conventional magnetic resonance imaging (MRI), which detects the 1 H resonance signal from tissue water, is a powerful imaging modality for characterizing a wide variety of organs. However, lungs present a unique challenge for MRI and 1 H studies of lung suffer from a number of factors, including low water content within the lung and short T 2 and T 2 * relaxation times caused by variations in magnetic susceptibility associated with the many air-tissue interfaces of the alveoli and bronchioles that reduce sensitivity and can limit available information. By contrast, hyperpolarized (HP) 3 He MRI detects helium gas introduced directly into the gas-exchange spaces of the lung. The imaging of hyperpolarized gas enables studies of both lung structure and function that are not possible with other methods. Previous studies of human and animal lungs have demonstrated the utility of hyperpolarized 3 He magnetic resonance lung imaging techniques and have proven particularly effective at detecting and tracking ventilation defects. These techniques can, therefore, be extremely useful in studying diseases of the lung that are characterized by such defects (1-7). In addition, in vivo measurements of the 3 He apparent diffusion coefficient (ADC) in emphysema have effectively quantified lung structure by measuring its restrictive effects on the motion of 3 He gas atoms (1), providing detection and longitudinal tracking of changes in microarchitecture resulting from disease destruction of alveolar walls. HP 3 He lung MRI studies of emphysema in humans (1-5) and a variety of animals, including pigs, dogs, guinea pigs, and rats, have produced very promising results (6 -10). However, no applications of hyperpolarized 3 He magnetic resonance imaging to the mouse have been reported.Mouse models of disease are widely used in the medical research community and the availability of transgenic mouse models has greatly expanded the role of the mouse in preclinical research. HP 3 He MR imaging methods offer a potential means for studying a variety of lung disease models, including emphysema and lung cancer in the mouse. However, the small size of the mouse...

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ABSTRACT:The synchronization of MR data collection with respiration is essential for collecting high-quality, in vivo magnetic resonance images and spectra of rodents. In this article, we describe the design and operation of a simple, robust device for respiratory gating. Inexpensive and easy to construct, the device operates in either free-breathing or actively driven (ventilator) modes. Respiration is monitored either by a pressure transducer connected to the nosecone used to deliver anesthesia to the animal or by a fiber-optic detector of the animal's motion. The device generates a TTL signal that can be used to trigger the MR scanner to enable respiratory-synchronized data acquisition. A variety of different MR imaging sequences can be easily modified to incorporate respiratory gating. We present respiratory-synchronized imaging and spectroscopy results obtained using this device, including 1 H MR images of mouse lung, liver, and spinal cord and localized 1 H spectra of mouse liver.