The task group ͑TG͒ for quality assurance of medical accelerators was constituted by the American Association of Physicists in Medicine's Science Council under the direction of the Radiation Therapy Committee and the Quality Assurance and Outcome Improvement Subcommittee. The task group ͑TG-142͒ had two main charges. First to update, as needed, recommendations of Table II of the AAPM TG-40 report on quality assurance and second, to add recommendations for asymmetric jaws, multileaf collimation ͑MLC͒, and dynamic/virtual wedges. The TG accomplished the update to TG-40, specifying new test and tolerances, and has added recommendations for not only the new ancillary delivery technologies but also for imaging devices that are part of the linear accelerator. The imaging devices include x-ray imaging, photon portal imaging, and cone-beam CT. The TG report was designed to account for the types of treatments delivered with the particular machine. For example, machines that are used for radiosurgery treatments or intensity-modulated radiotherapy ͑IMRT͒ require different tests and/or tolerances. There are specific recommendations for MLC quality assurance for machines performing IMRT. The report also gives recommendations as to action levels for the physicists to implement particular actions, whether they are inspection, scheduled action, or immediate and corrective action. The report is geared to be flexible for the physicist to customize the QA program depending on clinical utility. There are specific tables according to daily, monthly, and annual reviews, along with unique tables for wedge systems, MLC, and imaging checks. The report also gives specific recommendations regarding setup of a QA program by the physicist in regards to building a QA team, establishing procedures, training of personnel, documentation, and end-to-end system checks. been considerably expanded as compared with the original TG-40 report and the recommended tolerances accommodate differences in the intended use of the machine functionality ͑non-IMRT, IMRT, and stereotactic delivery͒.

A 16-residue peptide [(Ala-Glu-Ala-Glu-AlaLys-Ala-Lys)2J has a characteristic 13-sheet circular dichroism spectrum in water. Upon the addition of salt, the peptide spontaneously assembles to form a macroscopic membrane. The membrane does not dissolve in heat or in acidic or alkaline solutions, nor does it dissolve upon addition of guanidine hydrochloride, SDS/urea, or a variety of proteolytic enzymes.Scanning EM reveals a network of interwoven framents ""10-20 nm in diameter. An important component of the stability is probably due to formation of complementary ionic bonds between glutamic and lysine side chains. This phenomenon may be a model for studying the insoluble peptides found in certain neurological disorders. It may also have implications for biomaterials and origin-of-life research.Peptides of alternating hydrophilic and hydrophobic amino acid residues have a tendency to adopt a (3-sheet structure. The complete sequence of (Ala-Glu-Ala-Glu-Ala-Lys-AlaLys)2 (EAK16) was originally found in a region of alternating hydrophobic and hydrophilic residues in zuotin, a yeast protein that was initially identified for its ability to bind preferentially to left-handed Z-DNA (1). Previous studies with alternating amphiphilic-peptide polymers-e.g., poly-(Val-Lys), poly(Glu-Ala), poly(Tyr-Glu), poly(Lys-Phe), poly(Lys-Leu)-and oligopeptides [(Val-Glu-Val-Orn)j_3]-Val (2-7) have shown that these polymers can adopt (3-sheet structures and can aggregate, depending upon pH, salt, and time. However, self-complementary EAK16 is distinctive in that it forms an insoluble macroscopic membrane. MATERIALS AND METHODSPeptides. The Glu-Ala-Lys peptides were synthesized by a peptide synthesizer (Applied Biosystems), purified by reverse-phase HPLC, and eluted by a linear gradient of 5-80% acetonitrile/0.1% trifluoacetic acid. The peptide stock solutions were dissolved in water (1-5 mg/ml) or in 23% acetonitrile (10 mg/ml). The concentrations of the peptides were determined by dissolving dried peptide in water (wt/vol) and centrifuging the solution. A portion of the solution was then analyzed by hydrolysis with internal controls. The sequence of the peptides was confirmed by microsequencing. The composition of the peptides was confwrmed by hydrolytic analysis. Ala-Glu-Ala-Lys-Ala-Glu-Ala-Glu-Ala-Lys-AlaLys (EAK12) and EAK16 are acetylated and aminated at the N-and C-terminal ends, respectively. Blocking of both N and C termini of EAK16 appears nonessential for membrane formation.CD Measurement. CD spectra were gathered on an Aviv model 6ODS spectropolarimeter with 6OHDS software for data processing. Because EAK16 contains both positively and negatively charged residues, the peptide itself can serve as a buffer. CD samples were prepared by diluting stock peptide solution (1-5 mg/ml) in water.Membrane Preparations. The membranes were prepared as follows: 5-10 ,4 of the stock solution of EAK16 peptide (1-5 mg/ml) was added to 0.5-1.0 ml of phosphate-buffered saline (150 mM NaCl/10 mM sodium phosphate, pH 7.4) with 0.00001% Con...

A new type of self-assembling peptide (sapeptide) scaffolds that serve as substrates for neurite outgrowth and synapse formation is described. These peptide-based scaffolds are amenable to molecular design by using chemical or biotechnological syntheses. They can be tailored to a variety of applications. The sapeptide scaffolds are formed through the spontaneous assembly of ionic self-complementary ␤-sheet oligopeptides under physiological conditions, producing a hydrogel material. The scaffolds can support neuronal cell attachment and differentiation as well as extensive neurite outgrowth. Furthermore, they are permissive substrates for functional synapse formation between the attached neurons. That primary rat neurons form active synapses on such scaffold surfaces in situ suggests these scaffolds could be useful for tissue engineering applications. The buoyant sapeptide scaffolds with attached cells in culture can be transported readily from one environment to another. Furthermore, these peptides did not elicit a measurable immune response or tissue inflammation when introduced into animals. These biological materials created through molecular design and self assembly may be developed as a biologically compatible scaffold for tissue repair and tissue engineering.biological materials ͉ cell attachment ͉ molecular material design ͉ primary neurons ͉ PC12 cells