Inverse treatment planning for an electronic brachytherapy system delivering anisotropic radiation therapy.

An inverse radiation treatment planning algorithm for Sensus Healthcare's SculpturaTM electronic brachytherapy system has been designed. The algorithm makes use of simulated annealing to optimize the conformation number (CN) of the treatment plan. The highly anisotropic dose distributions produced by the SculpturaTM x-ray source empower the inverse treatment planning algorithm to achieve highly conformal treatment plans for a wide range of prescribed planning target volumes. Over a set of 10 datasets the algorithm achieved an average CN of 0.79 ± 0.08 and an average gamma passing rate of 0.90 ± 0.10 at 5%/5 mm. A regularization term that encouraged short treatment plans was used, and it was found that the total treatment time could be reduced by 20% with only a nominal reduction in the CN and gamma passing rate. It was also found that downsampling the voxelized volume (from 3203 to 643 voxels) prior to optimization resulted in a 150× speedup in the optimization time (from 2 + minutes to < 1 s) without affecting the quality of the treatment plan.

Characterization of an x-ray source with a partitioned diamond-tungsten target for electronic brachytherapy with 3D beam directionality.

The Sculptura™ is a new high-dose-rate electronic brachytherapy system developed by Sensus Healthcare. By combining a steerable electron beam with a partitioned diamond-tungsten x-ray target, the x-ray source of the Sculptura™ is capable of producing highly anisotropic dose distributions, thus achieving true 3D beam directionality. This article reports the spectral and dosimetric characterization of the Sculptura™ x-ray source through a combination of measurements and Monte Carlo simulations for operating points between 50-100 kV. Excellent agreement (~5% discrepancy) between the simulations and measurements was obtained for in-air dose rate characterization. The validated simulations were then used to calculate the dose distribution in water. Dose rates of >2 cGy/min/µA can be produced at 100 kV, thus delivering 10 Gy in 1 min for typical operating conditions. The dose distributions are sharply peaked, with a full-width at half-maximum azimuth of about 100°.

Offline impedance measurements for detection and mitigation of dangerous implant interactions: an RF safety prescreen.

PURPOSE: The concept of a "radiofrequency safety prescreen" is investigated, wherein dangerous interactions between radiofrequency fields used in MRI, and conductive implants in patients are detected through impedance changes in the radiofrequency coil. THEORY: The behavior of coupled oscillators is reviewed, and the resulting, observable impedance changes are discussed. METHODS: A birdcage coil is loaded with a static head phantom and a wire phantom with a wire close to its resonant length, the shape, position, and orientation of which can be changed. Interactions are probed with a current sensor and network analyzer. RESULTS: Impedance spectra show dramatic, unmistakable splitting in cases of strong coupling, and strong correlation is observed between induced current and scattering parameters. CONCLUSIONS: The feasibility of a new, low-power prescreening technique has been demonstrated in a simple phantom experiment, which can unambiguously detect resonant interactions between an implanted wire and an imaging coil. A new technique has also been presented which can detect parallel transmit null modes for the wire.