Susan B. Klein

Variations in the RBE for Cell Killing Along the Depth-Dose Profile of a Modulated Proton Therapy Beam

Considerable evidence now exists to show that that the relative biological effectiveness (RBE) changes considerably along the proton depth-dose distribution, with progressively higher RBE values at the distal part of the modulated, or spread out Bragg peak (SOBP) and in the distal dose fall-off (DDF). However, the highly variable nature of the existing studies (with regards to cell lines, and to the physical properties and dosimetry of the various proton beams) precludes any consensus regarding the RBE weighting factor at any position in the depth-dose profile. We have thus conducted a systematic study on the variation in RBE for cell killing for two clinical modulated proton beams at Indiana University and have determined the relationship between the RBE and the dose-averaged linear energy transfer (LETd) of the protons at various positions along the depth-dose profiles. Clonogenic assays were performed on human Hep2 laryngeal cancer cells and V79 cells at various positions along the SOBPs of beams with incident energies of 87 and 200 MeV. There was a marked variation in the radiosensitivity of both cell lines along the SOBP depth-dose profile of the 87 MeV proton beam. Using Hep2 cells, the D0.1 isoeffect dose RBE values (normalized against 60Co) were 1.46 at the middle of SOBP, 2.1 at the distal end of the SOBP and 2.3 in the DDF. For V79 cells, the D0.1 isoeffect RBE for the 87 MEV beam were 1.23 for the proximal end of the SOBP: 1.46 for the distal SOBP and 1.78 for the DDF. Similar D0.1 isoeffect RBE values were found for Hep2 cells irradiated at various positions along the depth-dose profile of the 200 MeV beam. Our experimentally derived RBE values were significantly correlated (P = 0.001) with the mean LETd of the protons at the various depths, which confirmed that proton RBE is highly dependent on LETd. These in vitro data suggest that the RBE of the proton beam at certain depths is greater than 1.1, a value currently used in most treatment planning algorithms. Thus, the potential for increased cell killing and normal tissue damage in the distal regions of the proton SOBP may be greater than originally thought.

Proton therapy for exudative age-related macular degeneration: a randomized, sham-controlled clinical trial☆

PURPOSE To examine the effect of proton beam irradiation on subfoveal choroidal neovascular membranes (CNVM) associated with age-related macular degeneration (AMD).Randomized, prospective, sham-controlled, double-masked treatment trial. METHODS Thirty-seven subjects with subfoveal CNVM due to AMD were randomly assigned to 16-Gy proton irradiation delivered in two fractions 24 hours apart or to sham control treatment. Recruitment was halted at 37 subjects for ethical reasons regarding randomization to sham treatment when Food and Drug Administration approval of Visudyne was anticipated. RESULTS Proton irradiation was associated with a trend toward stabilization of visual acuity, but this association did not reach statistical significance. No correlations were found within the fluorescein angiography data, including greatest linear dimension of CNVM total size, area of active leakage, area of associated subretinal hemorrhage, and intensity. CONCLUSIONS With the acceptance of photodynamic therapy, future studies will require more complex design and larger sample size to determine whether radiation can play either a primary or adjunctive role in treating these lesions.

EPR measurements showing that plasma membrane viscosity can vary from 30 to 100 cP in human epidermal cell strains

Abstract A rigorous technique for the measurement of human membrane viscosity by electron paramagnetic resonance (EPR) spectroscopy has been developed by designing a sample preparation procedure to optimize the spin labeling process and using a special (grown in essential fatty acid free medium) epidermal cell strain. The essential fatty acid deficient cell strains (keratinocytes) were also grown in fatty acid supplemented media formulated to alter the fatty acid composition of the phospholipids that form the cell membrane. Fatty acid free bovine serum albumin was used as a carrier for the spin label (16-doxyl stearate methyl ester) at an approximately equimolar ratio. Monolayers grown in T-75 flasks were labeled for 15 min at 4°C with 12 μM bovine serum albumin plus 20 μM spin label. The cells were then washed and transferred (at 4°C) to a flatcell for EPR studies at 37°C. The spectra were computer simulated and the results were interpreted by comparison with a “standard curve” obtained from the EPR spectra of the spin label in oil at multiple temperatures. Arguments are presented for preferring this measurement technique over the more conventional use of order parameters and over the use of some other spin labels. The EPR spectra were completely insensitive to the effects of molecular dioxygen in the growth medium and cytoplasm, but remarkabley sensitive to the fatty acid composition of the cellular phospholipids. Fatty acid modified epidermal cells showed a very strong correlation between membrane fluidity (a three-fold change in the membrane viscosity) and a fatty acid double bond index.

Comparison of Indiana University Cyclotron Facility Faraday cup proton dosimetry with radiochromic films, a calorimeter, and a calibrated ion chamber

The accuracy and utility of the dosimetry system used for radiation effects research with high energy protons at the Indiana University Cyclotron Facility, IUCF, has been confirmed by comparison with an independently calibrated Markus ion chamber, a Schulz water calorimeter and GAFCHROMIC/sup TM/ films.

Rapid RBE-Weighted Proton Radiation Dosimetry Risk Assessment.

Proton therapy dose is affected by relative biological effectiveness differently than X-ray therapies. The current clinically accepted weighting factor is 1.1 at all positions along the depth–dose profile. However, the relative biological effectiveness correlates with the linear energy transfer, cell or tissue type, and the dose per fraction causing variation of relative biological effectiveness along the depth–dose profile. In this article, we present a simple relative biological effectiveness-weighted treatment planning risk assessment algorithm in 2-dimensions and compare the results with those derived using the standard relative biological effectiveness of 1.1. The isodose distribution profiles for beams were accomplished using matrices that represent coplanar intersecting beams. These matrices were combined and contoured using MATLAB to achieve the distribution of dose. There are some important differences in dose distribution between the dose profiles resulting from the use of relative biological effectiveness = 1.1 and the empirically derived depth-dependent values of relative biological effectiveness. Significant hot spots of up to twice the intended dose are indicated in some beam configurations. This simple and rapid risk analysis could quickly evaluate the safety of various dose delivery schema.

An interferon resistant variant of the hairy-cell leukemic cell line, eskol : biochemical and immunological characterization

The B-lymphoblastoid cell line Eskol, which is composed of differentiated cells resembling hairy-cell leukemia, has been used to study the effects of type I interferon in vitro. In order to study the mechanism of delayed interferon therapy resistance, a hairy-cell leukemia-like clonal cell line (IREs-4) was isolated from Eskol after 4 months of exposure to r-metIFN-con1. When compared to Eskol cells, the IREs-4 cells were resistant to the antiproliferative effect of type I interferons as well as interferon induced protection against LAK cells. Treatment of IREs-4 with type I interferon did not induce MHC antigens, although both MHC class I and II antigens were induced in Eskol. Binding studies indicated the presence of equal numbers of high affinity binding sites with similar affinities on both cell lines. The resistant phenotype appears to result from an intracellular event which is essential to interferon signal transduction. It is hypothesized that this variant may reflect heterogeneity in the normal population of hairy-cell leukemia cells, and may explain the partial resistance of HCL patients to IFN therapy.

Status of the Proton Therapy Project at IUCF and the Midwest Proton Radiotherapy Institute

The first proton therapy patient was successfully treated for astrocytoma using a modified nuclear experimentation beam line and in‐house treatment planning in 1993. In 1998, IUCF constructed an eye treatment clinic, and conducted a phase III clinical trial investigating proton radiation treatment of AMD. Treatment was planned using Eyeplan modified to match the IUCF beam characteristics. MPRI was conceptualized in 1996 by a consortium of physicians and physicists. Reconfiguration began in 2000; construction of the achromatic trunk line began in 2001, followed by manufacture of 4 energy selection lines and two fixed horizontal beam treatment lines. Two isocentric, rotational gantries will be installed following completion of the horizontal beam lines. A fifth line will supply the full‐time radiation effects research station. Standard proton delivery out of the main stage is specified at 500 nA of 205 MeV. Clinic construction began in April, 2002 and will be completed by mid‐December. Design, construction ...

Radiation effects facilities, dosimetry, and program at the Indiana University cyclotron facility

High energy protons are useful for ground based simulation of the effects of space radiation on electronic devices and systems. Present and planned facilities to support the ongoing IUCF radiation effects research program (RERP), which uses protons with energies as high as 200 MeV, are described and results of high energy proton dosimetry studies are presented.

Chapter 13 The Nucleoprotein Hybridization Method for Isolating Active and Inactive Genes as Chromatin

Publisher Summary This chapter describes a method for fractionating chromatin that is based on specific hybridization between soluble chromatin fragments and oligonucleotides. This method, termed “nucleoprotein hybridization,” targets a specific gene on the basis of its DNA sequence. This technique makes it possible to isolate the chromatin of defined DNA sequence irrespective of its functional state. Alternative protocols for chromatin fractionation have employed differential solubility of chromatin fragments after mild nuclease digestion, immunoprecipitation, and mercury affinity columns. These alternative techniques yield a fraction enriched in active or inactive chromatin representing an ensemble of different genes. The chapter schematically represents seven steps of nucleoprotein hybridization. The feasibility of the technique has been proved with the SV40 model system. SV40 could be mixed with an excess of exogenous sea-urchin chromatin and then isolated to 88% purity corresponding to a 115-fold enrichment. The chapter also describes the first purification of active and inactive cellular genes as chromatin using the nucleoprotein hybridization. The Strongylocentrotus purpuratus sea urchin early histone gene repeat (SUEHGR) was chosen as a target for the first application of the technique.

Radiation Biology of Choroidal Neovascularisation of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a disorder of older people where there is progressive deterioration of central vision due to degenerative changes within the macula of the eye. The wet form of this disease is present in only one tenth of the individuals with AMD although it accounts for over 90% of those who suffer severe central visual loss (Ferris 1983). In the subgroup with wet AMD, the degenerative process results in the breakdown of the barrier between the choroid and the retina in the macular region and provokes growth of new vessels originating from the choriocapillaris (Gass 1967). These new vessels invade the sub-pigment epithelial and sub-retinal spaces and are accompanied by inflammatory cells, detached retinal pigment epithelial cells and fibroblasts. The new vessels are incompetent and leak fluid and blood, which are inimical to the health of the retinal pigment epithelium (RPE) and the photoreceptors.