Respiratory motion is difficult to compensate for with conventional radiotherapy systems. An accurate tracking method for following the motion of the tumor is of considerable clinical relevance. We investigate methods to compensate for respiratory motion using robotic radiosurgery. In this system the therapeutic beam is moved by a robotic arm, and follows the moving target through a combination of infrared tracking and synchronized x-ray imaging. Infrared emitters are used to record the motion of the patient's skin surface. The position of internal gold fiducials is computed repeatedly during treatment, via x-ray image processing. We correlate the motion between external and internal markers. From this correlation model we infer the placement of the internal target during time intervals where no x-ray images are taken. Fifteen patients with lung tumors have recently been treated with a fully integrated system implementing this new method. The clinical trials confirm our hypothesis that internal motion and external motion are indeed correlated. In a preliminar study we have extended our work to tracking without implanted fiducials, based on algorithms for computing deformation motions and digitally reconstructed radiographs.

Vertical GaN Schottky barrier diodes (SBDs) were fabricated on freestanding GaN substrates with low dislocation density. High quality n-GaN drift-layer with an electron mobility of 930 cm2 V-1 s-1 was obtained by optimizing the growth conditions by reducing the intensity of yellow luminescence using conventional photoluminescence measurements. The specific on-resistance (RonA) and the breakdown voltage (VB) of the SBDs were 0.71 mΩ cm2 and over 1100 V, respectively. The figure of merit (VB2/RonA) was 1.7 GW/cm2, which is the highest value among previously reported SBDs for both GaN and SiC.

We evaluated the efficacy and safety of stereotactic body radiation therapy (SBRT) for patients with head and neck tumors. From April 2005 through April 2008, 34 patients with head and neck tumors were treated with CyberKnife SBRT. Twenty-one of them had prior radiotherapy. Treatment sites were orbit (n = 7), cervical lymph nodes (n = 6), nasopharynx (n = 5), oropharynx (n = 4) and others (n = 12). The prescribed dose ranged from 19.5 to 42 Gy (median, 30 Gy) in 3-8 fractions for consecutive days. The target volume ranged from 0.7 to 78.1 cm(3) (median, 11.6 cm(3)). The median follow-up was 16 months. Treatment was well tolerated without significant acute complications in any cases. Complete response rate and partial response rate were 32.4% and 38.6%, respectively. The overall survival rates were 70.6% and 58.3% at 12 and 24 months, respectively. The overall survival was better in patients without prior radiotherapy within the previous 24 months or in case of smaller target volume. Six patients suffered severe late complications. All these patients had prior radiotherapy, and 2 of them developed massive hemorrhage in the pharynx and both died of this complication 5 and 28 months, respectively, after SBRT. Our preliminary results suggest that SBRT is an effective treatment modality for head and neck tumors. However, re-irradiation has significant risk of severe and even fatal late complications in the form of necrosis and hemorrhage in re-irradiated areas.

Acute toxicity with this method was acceptable. Further patient accrual and longer follow-up will allow comparison to other techniques.

Identifying the location of deposits of gamma emitting materials within storage vessels is of interest in the nuclear industry. A model example is presented involving an idealized cone-shaped deposit of gamma emitting material contained within a vessel. The purpose of this study is to determine whether useful information regarding the gamma emitting deposit can be obtained from a dataset of very limited size and quality. The inverse problem of determining the size and location of the deposit from a very limited number of measurements taken outside the tank is not a straightforward matter. Failure of a Gauss-Newton implementation of the regularized least squares method has led the authors to consider a Markov chain Monte Carlo approach, which gives improved robustness and a credibility region for the estimates that quantifies the reliability of the tomographic reconstruction.