Three-dimensional structure determination from a single view

The ability to determine the structure of matter in three dimensions has profoundly advanced our understanding of nature. Traditionally, the most widely used schemes for 3D structure determination of an object are implemented by acquiring multiple measurements over various sample orientations, as in the case of crystallography and tomography (1,2), or by scanning a series of thin sections through the sample, as in confocal microscopy (3). Here we present a 3D imaging modality, termed ankylography (derived from the Greek words ankylos meaning 'curved' and graphein meaning 'writing'), which enables complete 3D structure determination from a single exposure using a monochromatic incident beam. We demonstrate that when the diffraction pattern of a finite object is sampled at a sufficiently fine scale on the Ewald sphere, the 3D structure of the object is determined by the 2D spherical pattern. We confirm the theoretical analysis by performing 3D numerical reconstructions of a sodium silicate glass structure at 2 Angstrom resolution and a single poliovirus at 2 - 3 nm resolution from 2D spherical diffraction patterns alone. Using diffraction data from a soft X-ray laser, we demonstrate that ankylography is experimentally feasible by obtaining a 3D image of a test object from a single 2D diffraction pattern. This approach of obtaining complete 3D structure information from a single view is anticipated to find broad applications in the physical and life sciences. As X-ray free electron lasers (X-FEL) and other coherent X-ray sources are under rapid development worldwide, ankylography potentially opens a door to determining the 3D structure of a biological specimen in a single pulse and allowing for time-resolved 3D structure determination of disordered materials.Comment: 30 page

WE‐C‐BRB‐06: Antiproton Radiotherapy: Development of Physically and Biologically Optimized Monte Carlo Treatment Planning Systems for Intensity and Energy Modulated Delivery.

Purpose: Antiprotons have become of interest in radiotherapy due to their higher peak to plateau dose ratio relative to protons and carbon ions, and a beneficial increase in RBE towards the Bragg peak as recently verified by experimental investigations of the AD‐4 collaboration at CERN. An obstacle limiting further research is the lack of a treatment planning system capable of concurrently optimizing the necessary modulation of intensity and energy, while accounting for the variation in biological effectiveness. Here we develop a Monte Carlo based treatment planning system for this purpose and subsequently quantify its performance. Materials and Methods: Dose kernels corresponding to different energy and source configurations were calculated using MCNPX in phantom and voxelized patient CT scans, and then converted to biological equivalent dose using depth dependent RBE weighting factors derived from theory and experiment. Linear equations were formulated for each pixel representing superposition of different kernels weighted by unknown intensities. Algorithms using constrained least square and gradient descent optimization were developed to minimize objective functions measuring the geometric correlation of the planning target volume (PTV) with the calculated distribution, yielding an optimized intensity for beams as function of energy and direction. Results: Biologically optimized treatment plans implemented on a voxelized 38 year old human were in good agreement with the input PTVs, reproducing the PTVs with a mean error of less than 2.24%. Proof of principle demonstrations were successful in producing complicated structures, such resemblance of Einstein, in water phantom with a correlation greater than 93%. Conclusions: We have developed a Monte Carlo treatment planning system for energy and intensity modulated antiproton therapy capable of incorporating depth‐dependency of the RBE, and reproducing complicated PTVs with high accuracy. The work can be readily extended to incorporate more sophisticated objective functions such as NTCP and TCP functionals

MO‐E‐AUD B‐02: Antiproton Therapy: Monte Carlo Simulations of Normal Tissue Equivalent Dose From Annihilation Neutrons.

Purpose: Recent in vitro experiments at CERN have demonstrated a superior biological effectiveness for antiprotons relative to protons. A continued concern is the normal tissue dose resulting from annihilation neutrons. Using Monte Carlo simulations of a CT‐based anthropomorphic human phantom, we quantify the physical dose from annihilation byproducts and present the first organ specific calculations of normal tissue equivalent dose from neutrons in antiproton therapy. Method and Materials: MCNPX and FLUKA were utilized to model antiproton irradiation of the segmented whole‐body phantom of a 38 year old male representing the ICRP reference man. The fluence was tallied as a function of energy and organ type for a 75 MeV antiproton pencil beam with a Bragg peak located in the frontal lobe of the phantom's brain. Physical dose was calculated for each organ as a function of energy using fluence to kerma conversion coefficients (ICRU‐63). Finally, using energy dependent radiation weighting factors (ICRP‐60), the equivalent dose from neutrons was estimated for each organ. Results: The results indicate a neutron fluence on the order of 10 −5 cm −2 per incident antiproton for the bladder and colon, and a neutron fluence on the order of 10 −4 cm −2 per incident antiproton for the thyroid and esophagus. As anticipated, the physical and equivalent doses are dependent on the irradiation geometry and the proximity of the organs to the Bragg peak; of the organs tallied, bone and thyroid received the highest physical and equivalent dose for the given irradiation protocol. The estimates of organ physical and equivalent dose and their uncertainties are discussed. Conclusion: We have developed an anthropomorphic Monte Carlo model for antiproton therapy. The model provides a method for more sophisticated biological modeling of treatment response such as cost basis analysis of TCP and NTCP relative to other treatment modalities