The crystal and molecular structure of pyridinium periodate [H 5 C 5 NH] + [IO 4 ] − (hereafter referred to as PyIO 4 ) was re-determined by single-crystal neutron diffraction at 350, 300 and 100 K. The structures of the high-temperature paraelectric and the ferroelectric intermediate phase confirmed the x-ray results. The low-temperature ferroelectric phase at 100 K, for which x-ray results did not agree with dielectric measurements, was uniquely determined by neutron diffraction. The sequence of space groups and continuous phase transitions is Cmcm(I)The structure of the lowtemperature phase III is consistent with all physical measurements. The continuous phase transition at T 2 = 210 K is not just accompanied by symmetry lowering but also by reversible twinning by pseudo-merohedry. The dipole moment of the ions of the low ferroelectric phase was calculated using the Gaussian 98 program. The theoretical value agrees well with the experimental spontaneous polarization measurements from the pyroelectric effect. The PyIO 4 belongs to the order-disorder class of ferroelectrics.

During TBI using the translation method, dose distribution and dose homogeneity can be easily controlled in selected points by means of semiconductor probes. Semiconductor probes are recommended for further use in the physical evaluation of TBI.

PURPOSE: High-dose-rate (HDR) brachytherapy (BRT) and stereotactic body radiotherapy (SBRT) are currently the two treatment options for definitive radiotherapy of prostate cancer, employing extreme hypofractionation. There are only very few studies comparing their dosimetry, all using computed tomography for treatment planning. We present here a real-word dosimetric comparison between SBRT and ultrasound-based virtual HDR-BRT, with both imaging modalities coming from the same patient. METHODS AND MATERIALS: Patients with prostate cancer on a prospective trial evaluating the toxicity of robotic-based SBRT were treated to a total dose of 35 Gy in 5 fractions. Fifteen patients were included in this analysis. During ultrasound-based fiducial implantation, a threedimensional data set as in real HDR-BRT procedure was acquired. Virtual HDR-BRT plans were generated and various organs at risk and prostate dosimetric parameters were evaluated. RESULTS: Concerning prostate, SBRT achieved significant higher D 98 , V 35 Gy, and V 37.5 Gy coverage, whereas virtual HDR-BRT achieved significant higher intratumoral doses reflected in the V 42 Gy and V 52.5 Gy. Rectal D max , V 36 Gy, and V 29 Gy were significantly lower for HDR-BRT with no difference as for V 18 Gy. SBRT was significantly inferior regarding bladder dosimetry (D max , V 36 Gy, V 18 Gy), whereas urethra D max and V 44 Gy where significantly higher at the expense of HDR-BRT. CONCLUSIONS: HDR-BRT is superior regarding rectum and bladder dosimetry, with SBRT being superior relative to urethra dosimetry. A randomized study is warranted to define the best extreme hypofractionated modality.

The structure of the free-acid form of the coenzyme NAD(+) was determined at 100 K from a single-crystal neutron experiment. NAD(+) is the oxidized form of the coenzyme redox pair NAD(+)/NADH and plays an important role in the catalysis of biological processes. The molecule crystallizes in space group P1 with one NAD(+) and four water molecules per unit cell. The structure is compared with the previous X-ray models of NAD(+) [Reddy et al. (1981), J. Am. Chem. Soc. 103, 907-914; Parthasarathy & Fridey (1984b), Science, 226, 969-971; Guillot et al. (2000), Acta Cryst. C56, 726-728]. The crystal packing and the hydrogen-bond pattern are discussed as well as four short C-H.O contacts involving the pyridine and adenine rings. The structure displays stereochemical distortions owing to the hydrogen bonding and crystal-packing constraints, reflecting the adaptability of the NAD(+) molecule in various chemical environments.

Effective single particle potentials governing the motion of O2 and N3- anions have been determined by single crystal neutron diffraction at high temperatures for three samples of ZrO2 doped with different amounts of Y and N. Diffusion jumps take place directly to vacant nearest neighbour anion sites through the edges of the surrounding cation tetrahedra along (100)-directions. Activation enthalpies of migration for O (1.09 eV) and N (1.99 eV) are in good agreement with values obtained from tracer diffusion measurements (M. Kilo, C. Argirusis, G. Borchardt and R. A. Jackson, Phys. Chem. Chem. Phys., 2003, 5, 2219 and M. Kilo, M. A. Taylor, C. Argirusis, G. Borchardt, M. Lerch, O. Kaitasov and B. Lesage, Phys. Chem. Chem. Phys., 2004, 6, 3645). The diffusion process is facilitated by local short range order and anharmonic thermal vibrations. It is therefore advocated that the interactions with the phonons have to be taken into account in the description of the diffusion process.

The gamma evaluation indicates good correlation between predicted and acquired EPID images. The EPID-based pretreatment IMRT verification method will help to improve the quality assurance procedure.

The results for registration allow an extensive dose reduction in both treatment areas. Very low mAs, however, do not qualify for clinical use because subjective judgment of the registration process is impossible. Compared to default presets the use of settings for acceptable image quality already permit a decrease in exposure of about 40 % (29.0 to 16.7 mGy) in prostate scans and 60 % (18.3 to 7.7 mGy) in chest scans.

Good VMC++ accuracy combined with moderate computing times of 1-15 min per beam satisfy all clinical needs. VMC++ allows, for the first time, accurate routine dose evaluations of radiation therapy with electrons. Adequate positioning of the dose reference point is essential. Even small displacements may significantly influence the calculation of monitor units.