Intracranial radiosurgery in the Netherlands. A planning comparison of available systems with regard to physical aspects and workload.

Different planning and treatment systems for intracranial stereotactic radiosurgery available in the Netherlands are compared. The systems for intracranial radiosurgery include: Gamma Knife, Cyberknife, Novalis, and Tomotherapy. Electronic data of 5 patients was transferred to all participating centres and treatment plans were generated according to 2 different prescription protocols. For this study, plans were also generated for a conventional linac. Even systems with a high resolution (Gammaknife and Novalis) have conformity indices in violation with RTOG guidelines (CI > 2.5) when target volumes of <0.5 cc are treated. For medium sized targets (0.5-1 cc) all systems performed reasonably well, but for the different systems a large range of conformity indices was seen (1.1 to 3.7). The differences are partly system dependent but depend also on specific planning choices made. For larger target volumes (> 1 cc), all systems perform well. The workload of the different techniques was comparable although the treatment times were usually longer for Gamma Knife radiosurgery. We conclude that small targets should be treated by dedicated systems, larger volumes (> 0.5-1 cc) can also be treated using conventional treatment systems equipped with a MLC.

Disordered exciton model for the core light-harvesting antenna of Rhodopseudomonas viridis.

In this work we explain the spectral heterogeneity of the absorption band (. Biochim. Biophys. Acta. 1229:373-380), as well as the spectral evolution of pump-probe spectra for membranes of Rhodopseudomonas (Rps.) viridis. We propose an exciton model for the LH1 antenna of Rps. viridis and assume that LH1 consists of 24-32 strongly coupled BChl b molecules that form a ring-like structure with a 12- or 16-fold symmetry. The orientations and pigment-pigment distances of the BChls were taken to be the same as for the LH2 complexes of BChl a-containing bacteria. The model gave an excellent fit to the experimental results. The amount of energetic disorder necessary to explain the results could be precisely estimated and gave a value of 440-545 cm(-1) (full width at half-maximum) at low temperature and 550-620 cm(-1) at room temperature. Within the context of the model we calculated the coherence length of the steady-state exciton wavepacket to correspond to a delocalization over 5-10 BChl molecules at low temperature and over 4-6 molecules at room temperature. Possible origins of the fast electronic dephasing and the observed long-lived vibrational coherence are discussed.

Polarized site-selective fluorescence spectroscopy of the long-wavelength emitting chlorophylls in isolated Photosystem I particles of Synechococcus elongatus.

Isolated trimeric Photosystem I complexes of the cyanobacterium Synechococcus elongatus have been studied with absorption spectroscopy and site-selective polarized fluorescence spectroscopy at cryogenic temperatures. The 4 K absorption spectrum exhibits a clear and distinct peak at 710 nm and shoulders near 720, 698 and 692 nm apart from the strong absorption profile located at 680 nm. Deconvoluting the 4 K absorption spectrum with Gaussian components revealed that Synechococcus elongatus contains two types of long-wavelength pigments peaking at 708 nm and 719 nm, which we denoted C-708 and C-719, respectively. An estimate of the oscillator strengths revealed that Synechococcus elongatus contains about 4-5 C-708 pigments and 5-6 C-719 pigments. At 4 K and for excitation wavelengths shorter than 712 nm, the emission maximum appeared at 731 nm. For excitation wavelengths longer than 712 nm, the emission maximum shifted to the red, and for excitation in the far red edge of the absorption spectrum the emission maximum was observed 10-11 nm to the red with respect to the excitation wavelength, which indicates that the Stokes shift of C-719 is 10-11 nm. The fluorescence anisotropy, as calculated in the emission maximum, reached a maximal anisotropy of r=0.35 for excitation in the far red edge of the absorption spectrum (at and above 730 nm), and showed a complicated behavior for excitation at shorter wavelengths. The results suggest efficient energy transfer routes between C-708 and C-719 pigments and also among the C-719 pigments.

Time-resolved and steady-state spectroscopic analysis of membrane-bound reaction centers from Rhodobacter sphaeroides: comparisons with detergent-solubilized complexes.

The spectroscopic analysis of the antenna-deficient Rhodobacter sphaeroides strain RCO1 has been extended to an investigation of the kinetics and spectroscopy of primary charge separation. Global analysis of time-resolved difference spectra demonstrated that the rate of charge separation in membrane-bound reaction centers is slightly slower than in detergent-solubilized reaction centers from the same strain. A kinetic analysis of the decay of the primary donor excited state at single wavelengths was carried out using a high repetition rate laser system, with the reaction centers being maintained in the open state using a combination of phenazine methosulfate and horse heart cytochrome c. The kinetics of primary charge separation in both membrane-bound and solubilized reaction centers were found to be non-monoexponential, with two exponential decay components required for a satisfactory description of the decay of the primary donor excited state. The overall rate of charge separation in membrane-bound reaction centers was slowed if the primary acceptor quinone was reduced using sodium ascorbate. This slowing was caused, in part, by an increase in the relative amplitude of the slower of the two exponential components. The acceleration in the rate of charge separation observed on removal of the reaction center from the membrane did not appear to be caused by a significant change in the electrochemical properties of the primary donor. The influence of the environment of the reaction center on primary charge separation is discussed together with the origins of the non-monoexponential decay of the primary donor excited state.

Spectroscopic properties of the light-harvesting complexes from Rhodospirillum molischianum.

Spectroscopic properties, including low-temperature absorbance, linear and circular dichroism and site-selection fluorescence of the antenna complexes from Rhodospirillum molischianum have been determined. The unique 'LH1-like' character of the amino acid sequence from LH2 of this bacterium is reflected in the circular dichroism of the B850 band of this complex. The wavelength dependence of the polarization of the LH2 complex shows an unusual shape that is attributed to the octameric state of this complex. The complete amino acid sequence for the LH1 alpha-polypeptide and most of the beta-polypeptides are presented. These conform to the general features of other LH1 polypeptides. This result, in combination with spectroscopic data for LH1 imply that the organisation of the core in this bacterium is not much different from that in other purple non-sulphur bacteria.