SU-E-T-635: Effect of Planning Parameters on Tomotherapy Dosimetric Quality and Treatment Efficiency

PURPOSE

To investigate how the setting of optimization parameters, fractional dose and tuning structure in tomotherapy treatment planning affects plan dosimetric quality and treatment efficiency.

METHODS

A digital phantom to simulate head and neck radiotherapy was constructed for this study. Tumor was 10cm long C-shaped with two surrounding parallel normal structures (P-NS) and one serial normal structure (S-NS). Dose prescription was 54 Gy in total. Fourteen treatment plans were generated with varied parameters in five categories: a) jaw size (1 to 5cm), b) pitch (0.215 to 0.43), c) modulation factor (1.5 to 4), d) dose per fraction (100 to 600cGy) and e) whether to use tuning structure. Plans were compared with multiple dosimetric endpoints including target minimum/maximum/mean dose, V100%, conformity, heterogeneity, S-NS maximum dose, P-NS and body mean dose, and treatment times. The reference plan was defined for the plan with conventional parameters: jaw 2.5cm, pitch 0.287, modulation factor 3.0, 200cGy per fraction and use of a 2cm ring structure in optimization.

RESULTS

Compared with 2.5cm jaw reference plan, 1cm jaw plan decreased the mean body dose 10.7% while 5 cm jaw plan increased the dose 17.9%. Smaller pitch (p=0.215) made the plan more conform than reference plan, and bigger pitch (p=0.43) had opposite effect. A small modulation factor (M=1.5) failed to spare critical structures. A medium modulation factor (M=2) resulted in similar plan to the reference but with 29% less treatment time. A low fractional dose (100 cGy) planned with similar parameter as reference had much inferior target coverage (V100%=85.6% vs V100%=96.4). Lastly, the use of tuning structure improved the conformity of target.

CONCLUSIONS

Selection of optimization parameters in tomotherapy treatment planning affects target coverage, critical structure sparing, body dose, and treatment time. Target coverage is compromised if fractional dose is low to the range of 100 cGy.

Trafficking-deficient G572R-hERG and E637K-hERG activate stress and clearance pathways in endoplasmic reticulum

Background

Long QT syndrome type 2 (LQT2) is the second most common type of all long QT syndromes. It is well-known that trafficking deficient mutant human ether-a-go-go-related gene (hERG) proteins are often involved in LQT2. Cells respond to misfolded and trafficking-deficient proteins by eliciting the unfolded protein response (UPR) and Activating Transcription Factor (ATF6) has been identified as a key regulator of the mammalian UPR. In this study, we investigated the role of ER chaperone proteins (Calnexin and Calreticulin) in the processing of G572R-hERG and E637K-hERG mutant proteins.

Methods

pcDNA3-WT-hERG, pcDNA3-G572R-hERG and pcDNA3-E637K-hERG plasmids were transfected into U2OS and HEK293 cells. Confocal microscopy and western blotting were used to analyze subcellular localization and protein expression. Interaction between WT or mutant hERGs and Calnexin/Calreticulin was tested by coimmunoprecipitation. To assess the role of the ubiquitin proteasome pathway in the degradation of mutant hERG proteins, transfected HEK293 cells were treated with proteasome inhibitors and their effects on the steady state protein levels of WT and mutant hERGs were examined.

Conclusion

Our results showed that levels of core-glycosylated immature forms of G572R-hERG and E637K-hERG in association with Calnexin and Calreticulin were higher than that in WT-hERG. Both mutant hERG proteins could activate the UPR by upregulating levels of active ATF6. Furthermore, proteasome inhibition increased the levels of core-glycosylated immature forms of WT and mutant hERGs. In addition, interaction between mutant hERGs and Calnexin/Calreticulin was stronger after proteasome inhibition, compared to WT-hERG. These results suggest that trafficking-deficient G572R-hERG and E637K-hERG mutant proteins can activate ER stress pathways and are targeted to the proteasome for degradation. Calnexin and Calreticulin play important roles in these processes.

P4-07-02: Detection, Enrichment, Characterization and Propagation of Circulating Tumour Cells from Patients with Advanced Metastatic Breast Cancer

Background: Circulating tumour cells (CTCs) have attracted much attention lately due to their potential utility in diagnostic, therapeutic and prognostic applications. Characterization of these cells may indeed permit more targeted and individualized therapeutic approaches, as well as provide a means to monitor treatment response. Although detection of CTCs in peripheral blood (PB) is relatively easy using current methodologies, characterization of the CTC pool has proven more challenging due to their low abundance. Furthermore, in-vitro expansion of this elusive cell pool in mammosphere cultures has not yet been reported. In order to achieve a more complete characterization of CTCs and attempt to obtain live cells in sufficient quantity for in vitro expansion, we have used aphaeresis as a means to collect a large initial cell fraction from which to enrich CTCs from peripheral blood.

Methods: A cohort (n=17) of late stage breast cancer patients were first screened using 10ml PB. Peripheral blood mononuclear cells (PBMCs) were isolated using a Ficoll gradient and then enriched for CTCs by anti-CD45 negative selection using an automated system (RoboSep) based on magnetic bead separation. CTCs were detected by immunocytochemistry (ICC) for cytokeratin expression and patients classified as CTC-positive were selected for the aphaeresis procedure. Following collection of aphaeresis material (APM), PBMCs were isolated using a Ficoll gradient, enriched by automated anti-CD45 negative selection and characterized for a variety of markers by ICC, immunofluorescence and flow cytometry. CTCs were then cultured in serum-free medium as monolayers and suspensions. Recovery at the various steps of the isolation process was determined using PB from healthy subjects spiked with MCF-7 breast cancer cells and processed using the same approach.

Results: Recovery of spiked MCF-7 cells was about 40% after Ficoll and magnetic bead separation. Using this negative selection procedure 17/17 (100%) of subjects tested were positive at screening. Most patients (14/17) underwent aphaeresis and a large number (9,600 to 108,000) of enriched CTCs was recovered from APM in all patients tested, either as individual cells or as CTC clusters. Using dual immunofluorescence labelling, co-localization of the epithelial cell marker CK8 and the chemokine receptor CXCR4 was observed within CTCs. Furthermore, over 20% of CTCs were positive for both CK8 and ALDH1, indicative of a stem-like phenotype. APM-derived CTCs from all patients (14/14) could be propagated, both as attached cells and in suspension culture. They formed colonies in monolayer culture, and clusters in mammosphere culture, indicating stem cell-like properties. They replicated for at least three passages in mammosphere culture.

Conclusion: Our CTC detection and enrichment method using negative selection offers a distinct advantage over current methodologies, including collection of clusters, and the ability to grow and expand CTCs in serum-free culture conditions. Furthermore, these cells demonstrate breast cancer stem cell-like characteristics, the ability to replicate for multiple passages as mammospheres in suspensions and a metastatic signature.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-07-02.

Ultralight metallic microlattices

Ultralight (<10 milligrams per cubic centimeter) cellular materials are desirable for thermal insulation; battery electrodes; catalyst supports; and acoustic, vibration, or shock energy damping. We present ultralight materials based on periodic hollow-tube microlattices. These materials are fabricated by starting with a template formed by self-propagating photopolymer waveguide prototyping, coating the template by electroless nickel plating, and subsequently etching away the template. The resulting metallic microlattices exhibit densities ρ ≥ 0.9 milligram per cubic centimeter, complete recovery after compression exceeding 50% strain, and energy absorption similar to elastomers. Young's modulus E scales with density as E ~ ρ(2), in contrast to the E ~ ρ(3) scaling observed for ultralight aerogels and carbon nanotube foams with stochastic architecture. We attribute these properties to structural hierarchy at the nanometer, micrometer, and millimeter scales.

Correlation of Formation Enthalpies with Critical Amorphization Temperature for Pyrochlore and Monazite

Systematic studies of a series of RE-titanate pyrochlore single crystals determined the formation enthalpies, ΔH0f-ox, and the critical amorphization temperature, Tc, the temperature above which the crystal can no longer be amorphized. A negative linear correlation was observed between ΔH0f-ox and Tc. In general as the cation radius ratio, RA/RB, decreases the formation enthalpy becomes less exothermic, i.e. the pyrochlore structure becomes less thermodynamically stable while the susceptibilty to ion beam-induced amorphization decreases. The opposite relation, i.e. a positive linear correlation between ΔH0f-ox and Tc was observed for a series of REPO4 single crystals with both the monazite and xenotime structures. Both relations can be understood in terms of pyrochlore and orthophosphate crystal chemistry, their formation of point defects, and the role of ion-irradiation induced phase transformations.

Ion Beam-Induced Amorphization of the Pyrochlore Structure-Type: A Review

This paper reviews the recent developments in the understanding of the radiation-damage processes in A2B2O7 (Fd3m; Z=8) pyrochlore-structure compounds. Pyrochlore structure compounds display a wide range of behaviors in response to ion beam irradiation. Some compositions, such as Gd2Ti2O7, are amorphized at relatively low doses (∼0.2 dpa at room temperature) while other compositions, such as Gd2Zr2O7, do not amorphize (even at doses of 36 dpa at 25 K) and instead disorder to a defect fluorite structure. The response to ion beam irradiation is highly dependent on compositional changes that affect both the structural distortion from the ideal fluorite structure and the associated energetics of the disordering process. Generally, the ionic size of the cations plays a dominant role in determining the radiation response of different pyrochlore compositions. However, the cation ionic radius ratio criteria cannot be applied all-inclusively in predicting the radiation “tolerance” of a pyrochlore. Systematic irradiation studies of the radiation response of rare-earth (A-site) pyrochlores in which B = Ti, Zr, and Sn have shown that the behavior of the pyrochlore also depends on the cation electronic structure, i.e., the type of bonding, which is closely related to the polyhedral distortion and structural deviation from the ideal fluorite structure. These structural changes affect the dynamic defect recovery process directly linked to the material's response to and recovery from irradiation.

Novel characteristics of a trafficking-defective G572R-hERG channel linked to hereditary long QT syndrome

BACKGROUND

The congenital long QT syndrome is a heterogeneous genetic disease associated with delayed cardiac repolarization, prolonged QT intervals, the development of ventricular arrhythmias and sudden death. Type 2 congenital long QT syndrome (LQT2) results from KCNH2 or hERG gene mutations. hERG encodes the K(v)11.1 alpha subunit of the rapidly activating delayed rectifier K(+) current in the heart. Studies of mutant hERG channels indicate that most LQT2 missense mutations generate trafficking-deficient K(v)11.1 channels.

OBJECTIVE

To identify the mechanism underlying G572R-hERG by using molecular and electrophysiological analyses.

METHODS AND RESULTS

To elucidate the electrophysiological properties of the G572R-hERG mutant channels, mutant hERG subunits were heterologously expressed in HEK293 cells alone or in combination with wild-type (WT)-hERG subunits. Patch-clamp techniques were used to record currents, and double immunofluorescence protein tagging and Western blotting were performed to examine the cellular trafficking of mutant subunits. When expressed alone, G572R-hERG subunits were not present in the cell membrane and did not produce detectable currents. When coexpressed with WT-hERG subunits, G572R-hERG decreased current density and altered gating properties of the WT-hERG channel.

CONCLUSION

The hERG-associated missense mutation G572R, like most LQT2 missense mutations, generates a trafficking-deficient phenotype. Furthermore, G572R-hERG causes a loss of function in hERG by a strong dominant negative effect on the WT-hERG channel.

Infrequent recovery of HIV from but robust exogenous infection of activated CD4(+) T cells in HIV elite controllers

BACKGROUND. Human immunodeficiency virus (HIV) elite controllers are able to control infection with HIV-1 spontaneously to undetectable levels in the absence of antiretroviral therapy, but the mechanisms leading to this phenotype are poorly understood. Although low frequencies of HIV-infected peripheral CD4(+) T cells have been reported in this group, it remains unclear to what extent these are due to viral attenuation, active immune containment, or intracellular host factors that restrict virus replication. METHODS. We assessed proviral DNA levels, autologous viral growth from and infectability of in vitro activated, CD8(+) T cell-depleted CD4(+) T cells from HIV elite controllers (mean viral load, <50 copies/mL), viremic controllers (mean viral load, <2000 copies/mL), chronic progressors, and individuals receiving highly active antiretroviral therapy. RESULTS. Although we successfully detected autologous virus production in ex vivo activated CD4(+) T cells from all chronic progressors and from most of the viremic controllers, we were able to measure robust autologous viral replication in only 2 of 14 elite controllers subjected to the same protocol. In vitro activated autologous CD4(+) T cells from elite controllers, however, supported infection with both X4 and R5 tropic HIV strains at comparable levels to those in CD4(+) T cells from HIV-uninfected subjects. Proviral DNA levels were the lowest in elite controllers, suggesting that extremely low frequencies of infected cells contribute to difficulty in isolation of virus. CONCLUSIONS. These data indicate that elite control is not due to inability of activated CD4(+) T cells to support HIV infection, but the relative contributions of host and viral factors that account for maintenance of low-level infection remain to be determined.

[A novel mutation of the KCNH2 gene in a family with congenital long QT syndrome]

OBJECTIVE

To perform mutation analysis in a family with long QT syndrome.

METHODS

The medical record of the affected child and his parents were collected. The locus of gene associated with the long QT syndrome was mapped by linkage analysis. Mutation analysis was done by PCR-single strand conformation polymorphism (SSCP) and direct sequencing.

RESULTS

A mutation (L539fs/47) and a SNP (L564L) were found in exon 7 of the KCNH2 gene of the proband. The mutation was from the father.

CONCLUSION

A novel mutation of L539fs/47 in the KCNH2 gene was identified in the LQTS family, which might be the disease-causing mutation for the family.

Fate of nonylphenol polyethoxylates and their metabolites in four Beijing wastewater treatment plants

Four Beijing wastewater treatment plants (WWTPs) were selected to investigate behaviours of nonylphenol polyethoxylates and their metabolites in different wastewater treatment processes. The results showed that the total concentrations of nonylphenolic compounds in the influents of the four WWTPs ranged from 0.115 to 0.347 mumol/L, as well as their removal efficiencies ranging from 75.7% to 90.8%. Both influent concentrations and removal efficiencies of nonylphenol polyethoxylates were correlated to seasons as follows: higher in the summer than in the winter, and influent concentrations were lower during the rain weather. The analysis revealed that 21.8-47.6% of nonylphenol polyethoxylates and their metabolites entering WWTPs were released via effluents and excess sludge, leaving a great part of them for biodegradation. Nonylphenol and short-chain nonylphenol polyethoxylates were disposed to the environment mainly via sewage sludge, while carboxylated nonylphenol polyethoxylates were the most abundant group of nonylphenol polyethoxylates in effluents.