Dosimetric Characterization of an Intensity-modulated X-Ray Brachytherapy System.

PURPOSE: An intensity-modulated X-ray brachytherapy system is being developed for various clinical applications. This new system makes it possible for clinical staff to control energy as well as dose rate for different tumor sites according to their sizes and radiobiological characteristics. MATERIALS AND METHODS: This system is mainly composed of an X-ray tube, guide tube collimation, and secondary (pseudo) target. Due to its configuration, convenient modulations of fluorescent X-ray energy and intensity are possible. To observe applicability of this novel system for various primary and secondary target combinations, Monte Carlo simulation using MCNP5 was performed, and air measurements were done. As a primary and pseudo-target combination, silver-molybdenum (Ag-Mo), tungsten-neodymium (W-Nd), and tungsten-erbium (W-Er) were used for the calculation for dose profile. Specifically, a dose distribution was calculated around each of these target combinations. Dose distributions as a function of target angles were also calculated. The Ag-Mo combination was analyzed for Cartesian coordinates of xy, xz, and yz planes of the pseudo-target to observe dose distribution as a function of the angle of secondary target. RESULTS: The results showed that radial dose fall-off of Ag-Mo was greater than commercially available brachytherapy sources (103 Pd and125 I) due to its low characteristic X-ray energy. CONCLUSIONS: Dose distribution variance should be considered in beam modulation for clinical application. Dynamic movement of the pseudo-target is feasible and remains as a subject for future research.

Assessment of gingival thickness using an ultrasonic dental system prototype: A comparison to traditional methods.

Knowledge of periodontal anatomy is essential when performing surgical and non-surgical procedures in the field of oral healthcare. Gingival thickness (GT) is often assessed for this purpose. A dental system prototype was recently developed for quantitative, non-invasive GT assessment by high-frequency (HF) ultrasound. Laboratory trials were conducted to validate system performance against a traditional method of assessment. A system with a 50 MHz broadband, spherically-focused transducer was used. The transducer was housed in a small, hand-held probe equipped with a continuous water supply. A-scans were obtained and thickness at each location was determined. For comparison, the traditional method of transgingival probing through tissue with an endodontic k-file needle was also implemented. Preliminary experiments were performed on phantoms simulating the anatomical and acoustic properties of human periodontal tissues. A porcine cadaver was obtained for further laboratory trials. The speed of sound through porcine gingiva was determined to be 1564 ± 21 m/s. Finally, a multiple-point experiment involved GT assessment in an array of locations on the buccal gingival surface in the fourth quadrant. Ultrasonic measurements were found to yield similar GT values to those obtained from invasive methods. Results obtained in this experiment validate the applicability of ultrasound as a diagnostic tool for assessing periodontal anatomy.

Enamel thickness measurement with a high frequency ultrasonic transducer-based hand-held probe for potential application in the dental veneer placing procedure.

This study presents a novel approach to measure the enamel thickness potentially applicable to the veneer placing procedure. All experiments have been carried out on the extracted human teeth, using a high frequency ultrasonic transducer (50 MHz, Sonix, Springfield, VA, USA). The enamel thickness measurement results obtained with high positional accuracy by a scanning acoustic microscope (Tessonics AM1103, Windsor, ON, Canada) were compared with the measurements conducted in a hand-held mode by using the same transducer placed in a custom fixture. Finally, to validate the ultrasonic measuring results, the samples were cut down the long axis to expose the cross-section. The enamel thickness was measured in several points along the selected part of the exposed cross-section by using an optical microscope (Stemi SV 11, Carl Zeiss AG, Jena, Germany). The values of the enamel thickness received by using the hand-held probe vs. the acoustic microscope were in close proximity (~10% difference) and were also satisfactory close to the enamel thickness results obtained from the direct cross-sectional measurements (~12% difference). The authors suggested a measuring procedure that allows avoiding errors related to the ultrasonic beam localization on the tooth surface. The high feasibility of the ultrasonic pulse-echo measurements in a hand-held mode was demonstrated.

X-ray scalpel - a new device for targeted x-ray brachytherapy and stereotactic radiosurgery.

The basic design and performance of a novel x-ray scalpel device for interstitial radiosurgery are reported. The x-ray scalpel is comprised of a capillary optics collimator conjugated with a high brilliance microfocus x-ray tube and a thin hollow needle (tip) attached to the collimator. The device is capable of producing a high dose rate (about 140 Gy min(-1) in water-like absorber at the exit window), 0.7 mm diameter, quasi-parallel beam that can be delivered to a targeted site by a minimally invasive procedure. Contrary to insertable x-ray tubes or radionuclides used in brachytherapy and complying with the 1/r(2) radiation attenuation law, the dose rate for a quasi-parallel beam decreases with distance as mu exp(-mu r), where mu is the energy-dependent linear attenuation coefficient in the exposed medium. Moreover, the shape, energy and the dose attenuation curve of the x-ray beam can be adjusted. Two versions of the x-ray scalpel device (5.4 keV and 20.2 keV) are described. We present results from our first test of the x-ray scalpel as a controllable source of focal radiation for producing radiation necrosis in rat brain tissue. Irradiation was transdurally delivered to the rat cerebral cortex for 10 min at a dose rate of 20 Gy min(-1).

A novel needle-based miniature x-ray generating system.

The basic concept, design and performance of a novel needle-based x-ray system for medical applications are reported. The main principle of the system is based on a two-stage production of x-rays. The system comprises a conventional x-ray tube with an Ag anode, any known type of conditioning optics and a 2.2 mm diameter hollow needle with an interchangeable Mo target. The target can be moved along the needle axis and rotated around the needle axis. The needle x-ray device allows for adjustment in energy and flux intensity of the x-rays emitted by the target. The depth dependence of the intensity, dose rate as well as spatial and energy distribution of the radiation emitted by the target have been experimentally measured. The depth dose rate results have been compared with theoretical calculations using a Monte Carlo simulation of the x-ray production process. These studies have experimentally confirmed that the concept of this x-ray system is correct. Further improvement of the device can increase the dose rate up to the levels required for clinical applications.