Host use patterns of Culicoides spp. biting midges at a big game preserve in Florida, U.S.A., and implications for the transmission of orbiviruses.

Culicoides spp. biting midges (Diptera: Ceratopogonidae) are vectors of pathogens that have a significant economic impact on the livestock industry. White-tailed deer (Odocoileus virginianus), a farmed species in the U.S.A., are susceptible to two Culicoides spp. borne orbiviruses: bluetongue virus and epizootic haemorrhagic disease virus. Elucidating host-vector interactions is an integral step in studying disease transmission. This study investigated the host range of Culicoides spp. present on a big game preserve in Florida on which a variety of Cervidae and Bovidae freely roam. Culicoides were captured with Centers for Disease Control and Prevention (CDC) miniature light traps run twice weekly on the preserve for 18 consecutive months (July 2015-December 2016). Host preference was quantified through forage ratios, based upon PCR-based bloodmeal analysis of Culicoides spp. and overall animal relative abundance on the preserve. Culicoides stellifer preferentially fed on Cervus spp. and fallow deer (Dama dama) and displayed a relative avoidance of Bovidae and white-tailed deer. Culicoides debilipalpis preferred white-tailed deer and avoided all Bovidae. Culicoides pallidicornis and Culicoides biguttatus showed preferences for white-tailed deer and Père David's deer (Elaphurus davidianus), respectively. These results add to current knowledge of preferred hosts of Florida Culicoides spp. and have implications for the spread of orbiviruses. Copyright © 2018 John Wiley & Sons, Ltd.

Radio frequency shielding for a linac-MRI system.

The real-time operation of a linac-MRI system will require proper radio frequency (RF) shielding such that the MRI images can be acquired without extraneous RF noise from the linac. We report on the steps taken to successfully shield the linac from the MRI such that the two devices can operate independently of one another. RF power density levels are reported internally and externally to the RF cage which houses the linac and MRI. The shielding effectiveness of the RF cage has been measured in the frequency range 1-50 MHz and is presented. Lastly MRI images of two phantoms are presented during linac operation. This work illustrates that the accelerating structure of a linac and an MRI can be housed within the same RF cage. The 6 MV linac can be operated to produce radiation with no measurable degradation in image quality due to RF effects.

First MR images obtained during megavoltage photon irradiation from a prototype integrated linac-MR system.

The authors report the first magnetic resonance (MR) images produced by their prototype MR system integrated with a radiation therapy source. The prototype consists of a 6 MV linac mounted onto the open end of a biplanar 0.2 T permanent MR system which has 27.9 cm pole-to-pole opening with flat gradients (40 mT/m) running under a TMX NRC console. The distance from the magnet isocenter to the linac target is 80 cm. The authors' design has resolved the mutual interferences between the two devices such that the MR magnetic field does not interfere with the trajectory of the electron in the linac waveguide, and the radiofrequency (RF) signals from each system do not interfere with the operation of the other system. Magnetic and RF shielding calculations were performed and confirmed with appropriate measurements. The prototype is currently on a fixed gantry; however, in the very near future, the linac and MR magnet will rotate in unison such that the linac is always aimed through the opening in the biplanar magnet. MR imaging was found to be fully operational during linac irradiation and proven by imaging a phantom with conventional gradient echo sequences. Except for small changes in SNR, MR images produced during irradiation were visually and quantitatively very similar to those taken with the linac turned off. This prototype system provides proof of concept that the design has decreased the mutual interferences sufficiently to allow the development of real-time MR-guided radiotherapy. Low field-strength systems (0.2-0.5 T) have been used clinically as diagnostic tools. The task of the linac-MR system is, however, to provide MR guidance to the radiotherapy beam. Therefore, the 0.2 T field strength would provide adequate image quality for this purpose and, with the addition of fast imaging techniques, has the potential to provide 4D soft-tissue visualization not presently available in image-guided radiotherapy systems. The authors' initial design incorporates a permanent magnet; however, other types of magnets and field strengths could also be incorporated. Usable MR images were obtained during linac irradiation from the linac-MR prototype. The authors' prototype design can be used as the functional starting point in developing real-time MR guidance offering soft-tissue contrast that can be coupled with tumor tracking for real-time adaptive radiotherapy.

Radiologic validation of a fast neutron multileaf collimator.

Teletherapy with high linear energy transfer radiations (LET), perhaps more than with low LET types, requires careful beam collimation to limit effects to normal structures. Intensity modulated techniques may also hold promise in this regard. Accordingly, a remote computer-controlled, high-resolution multileaf collimator (MLC) is placed into service at the Gershenson Radiation Oncology Center's fast neutron therapy center of the Karmanos Cancer Institute, Detroit, Michigan. Prior to clinical application the basic radiological properties of the fast neutron MLC are studied. Complicating the evaluation is the mixed neutron and gamma radiation field environment encountered with fast neutron beams. As a reference the MLC performance is compared to an existing multirod collimator (MRC) used at the facility for more than ten years. The MLC aggregate transmission is found to be about 4%, slightly outperforming the MRC. The measured gamma component for a closed collimator is 1.5 times higher for the MLC, compared with the MRC. The different materials used for attenuation, steel and tungsten, respectively account for the difference. The geometry for the MRC is double focused whereas that for the MLC is single focused. The resulting penumbrae agree between the focused axis of the MLC and both axes of the MRC. Penumbra differences between the focused and unfocused axes were not observable at small field sizes and a maximum of about 1 cm for a 25 x 25 cm2 field at 2.5 cm depth in water. For a 10 x 10 cm2 field the focused penumbra is 9 mm, and the unfocused is 12 mm. The many benefits of the fully automatic MLC over the semimanual MRC are considered to justify this compromise.

Compact multileaf collimator for conformal and intensity modulated fast neutron therapy: electromechanical design and validation.

The electromechanical properties of a 120-leaf, high-resolution, computer-controlled, fast neutron multileaf collimator (MLC) are presented. The MLC replaces an aging, manually operated multirod collimator. The MLC leaves project 5 mm in the isocentric plane perpendicular to the beam axis. A taper is included on the leaves matching beam divergence along one axis. The 5-mm leaf projection width is chosen to give high-resolution conformality across the entire field. The maximum field size provided is 30 x 30 cm2. To reduce the interleaf transmission a 0.254-mm blocking step is included. End-leaf steps totaling 0.762 mm are also provided allowing opposing leaves to close off within the primary radiation beam. The neutron MLC also includes individual 45 degrees and 60 degrees automated universal tungsten wedges. The automated high-resolution neutron collimation provides an increase in patient throughput capacity, enables a new modality, intensity modulated neutron therapy, and limits occupational radiation exposure by providing remote operation from a shielded console area.

Attenuation and activation characteristics of steel and tungsten and the suitability of these materials for use in a fast neutron multileaf collimator.

A computer controlled multileaf collimator (MLC) is being designed to replace the multirod collimator (MRC) at present used to shape the d(48.5) + Be neutron beam from the Harper Hospital superconducting cyclotron. The computer controlled MLC will improve efficiency and allow for the future development of intensity modulated radiation therapy with neutrons. The existing MRC uses tungsten rods, while the new MLC will use steel as the leaf material. In the current study the attenuation and activation characteristics of steel are compared with those of tungsten to ensure that (a) the attenuation achieved in the MLC is at least equivalent to that of the existing MRC, and (b) that the activation of the steel will not result in a significant change in the activation levels within the treatment room. The latter point is important since personnel exposure (particularly to the radiation therapy technologists) from induced radioactivity must be minimized. Measurement of the neutron beam attenuation in a broad beam geometry showed that a 30 cm thick steel leaf yielded 2.5% transmission. This compared favorably with the 4% transmission obtained with the existing MRC. Irradiation of steel and tungsten samples at different depths in a 30 cm steel block indicated that the activation of steel should be no worse than that of tungsten.

A multirod collimator for neutron therapy.

PURPOSE: To design, construct, and commission a multirod collimator for producing irregularly shaped fields in neutron radiation therapy. To demonstrate the reliability and applicability of this device to routine use with a superconducting cyclotron for neutron therapy. METHODS AND MATERIALS: A multirod collimator has been designed, constructed, and thoroughly tested to investigate its radiological properties; neutron transmission characteristics, beam profiles, and penumbral widths as a function of field size and depth in a phantom, and the spatial resolution of the rod array, have been measured. A wide variety of irregularly shaped fields, used routinely in neutron radiation therapy, have been produced, including fields that incorporate partial transmission blocks. The performance of the collimator has been closely monitored over a period of 20 months to accurately assess reliability. RESULTS: The multirod collimator has been in routine use for 32 months, and during this time a total of 7025 neutron fields has been treated. For the latter 20 months of this period, detailed performance records show that collimator failure has caused 28.4 h of downtime during the patient treatment day. Only 5.25 h of this downtime was experienced in the last 12 months (0.22% of the available treatment time). The results of collimator attenuation and beam profile measurements show that the radiological properties of the collimator are comparable to those of other collimator systems used for neutron radiation therapy. Isodose measurements in a water phantom show that the spatial resolution of the rods is superior to that of the leaves used in neutron multileaf collimators. The ability of the multirod collimator to produce many irregularly shaped fields commonly encountered in neutron radiation therapy has been demonstrated. Shaped fields for prostate, head and neck, soft tissue sarcomas, lung, thyroid, rectum, bladder, colon, breast, pancreas, and gynecological tumors have been produced. For some prostate cases, the device has been used to produce partial transmission blocks. CONCLUSIONS: A novel multirod collimator has been designed, constructed, and successfully applied in the routine treatment of neutron radiation therapy patients.

Cryogenic aspects of the operation of a superconducting cyclotron-based neutron therapy facility.

The Harper Hospital superconducting cyclotron, which is used for neutron radiation therapy, is a unique device. It is the first superconducting cyclotron to be installed in a hospital. The novel magnet cryostat can be rotated through 360 degrees without spilling liquid and whilst remaining vented to a low pressure return line for collection of the boil-off gas. The mode of operation of the cryogenic magnet is described in detail. Some of the problems associated with the cryogenic nature of the cyclotron including those problems encountered in operating a helium liquefaction system in a hospital are discussed. At the present time the magnet is kept cold by filling the cryostat with approximately 75 L of liquid helium each day before patient treatments begin. This is a time-consuming process. The possibility of modifying the helium gas recovery and liquefaction system so that a continuous liquid helium supply could be delivered to the magnet cryostat is discussed.

Radiological properties of a prototype multi-rod collimator for producing irregular fields in photon radiation therapy.

A prototype multi-rod collimator for producing irregular fields in photon radiation therapy has been designed and built. The mechanical details of the design and operation of the multi-rod collimator are discussed. Beam profiles for an approximately 10 x 10 cm2 field have been measured at various depths in phantom, and compared with profiles obtained using the secondary collimator jaws alone and with cast metal blocks. The ability of the collimator to produce irregular fields is demonstrated with reference to some commonly encountered therapy fields and the ability to produce central blocks and island blocks is discussed. Isodose curves for selected irregular fields are presented.

Transmission measurements in multi-rod arrays: a design study for a multi-rod collimator.

The results of transmission measurements for neutrons, cobalt-60 gamma-rays, and 10 and 15 MV photons made with close-packed arrays of tungsten rods are presented. These results indicate that tungsten rod arrays of reasonable thickness can provide for primary or secondary collimation of all these radiation beams. Development work on a collimation system utilizing the multi-rod concept which is capable of producing irregularly shaped fields and suitable for use in photon or neutron radiation therapy is described.

Coated intraocular lenses.

We found that an intraocular lens with a bonded coating of sodium hyaluronate caused less cell damage than an uncoated lens. We also found that an intraocular lens bonded with sodium hyaluronate will provide not only better adherence to viscoelastic materials and endothelial protection, but also may allow for better manipulation of the lens intraocularly. This is the first report of a sodium hyaluronate-coated intraocular lens used to prevent cell damage.