PubMed Health⌕ Search

Biomedical subjects

Craig Lewis

Publications and source records attributed to Craig Lewis.

5 recordsLinked to original sources
PubMed2006

Prostate contouring uncertainty in megavoltage computed tomography images acquired with a helical tomotherapy unit during image-guided radiation therapy.

PURPOSE: To evaluate the image-guidance capabilities of megavoltage computed tomography (MVCT), this article compares the interobserver and intraobserver contouring uncertainty in kilovoltage computed tomography (KVCT) used for radiotherapy planning with MVCT acquired with helical tomotherapy. METHODS AND MATERIALS: Five prostate-cancer patients were evaluated. Each patient underwent a KVCT and an MVCT study, a total of 10 CT studies. For interobserver variability analysis, four radiation oncologists, one physicist, and two radiation therapists (seven observers in total) contoured the prostate and seminal vesicles (SV) in the 10 studies. The intraobserver variability was assessed by asking all observers to repeat the contouring of 1 patient's KVCT and MVCT studies. Quantitative analysis of contour variations was performed by use of volumes and radial distances. RESULTS: The interobserver and intraobserver contouring uncertainty was larger in MVCT compared with KVCT. Observers consistently segmented larger volumes on MVCT where the ratio of average prostate and SV volumes was 1.1 and 1.2, respectively. On average (interobserver and intraobserver), the local delineation variability, in terms of standard deviations [Deltasigma = radical(sigma2MVCT-sigma2KVCT)], increased by 0.32 cm from KVCT to MVCT. CONCLUSIONS: Although MVCT was inferior to KVCT for prostate delineation, the application of MVCT in prostate radiotherapy remains useful.

Humans↗
PubMed2005

Measurement of dynamical forces between deformable drops using the atomic force microscope. I. Theory.

Recent experimental developments have enabled the measurement of dynamical forces between two moving liquid drops in solution using an atomic force microscope (AFM). The drop sizes, interfacial tension, and approach velocities used in the experiments are in a regime where surface forces, hydrodynamics, and drop deformation are all significant. A detailed theoretical model of the experimental setup which accounts for surface forces, hydrodynamic interactions, droplet deformation, and AFM cantilever deflection has been developed. In agreement with experimental observations, the calculated force curves show pseudo-constant compliance regions due to drop flattening, as well as attractive pull-off forces due mainly to hydrodynamic lubrication forces.

Journal Article↗
PubMed2004

Computed tomographic volumetric analysis as a predictor of local control in laryngeal cancers treated with conventional radiotherapy.

BACKGROUND: There is still controversy regarding the appropriate management of large T2 and T3 laryngeal cancers, with some investigators finding little correlation between the current TNM staging system and tumour control following external beam radiotherapy. OBJECTIVE: To establish the utility of computed tomography (CT)-determined tumour volume as a predictor of local control of moderately advanced (T2 and T3) squamous cell carcinoma of the larynx. MATERIALS AND METHODS: A retrospective chart review and CT volumetric analysis were performed on 47 patients who were treated for T2 or T3 laryngeal squamous cell carcinoma with radiotherapy alone at the London Regional Cancer Centre between 1995 and 2000. Of these 47 patients, there were 30 with glottic tumours and 17 with supraglottic tumours. Forty-two males and five females were included in the analysis, with ages ranging from 40 to 84 years. Each patient's CT scan was redigitized, and the tumours were outlined by the chief investigator and by a head and neck radiologist using anatomy modelling software. Patient demographics, tumour characteristics, and tumour stage were analyzed, with local failure rates described and related to the variables through univariate and multivariate analyses. RESULTS: Tumour size ranged from 0.15 to 16.64 cm3, with a mean volume of 3.5 cm3. The local recurrence rate in this group of patients was 40% (19/47). Local control was correlated on multivariate analysis to tumour size for all patients combined (> 3 cm3 vs < 3 cm3; p = .003) and for glottic tumours alone (> 1 cm3 vs < 1 cm3; p = .001). A correlation was also demonstrated on multivariate analysis between local control and overall stage (p = .023), patient age (p = .029), and hypopharyngeal involvement (p = .032). CONCLUSIONS: There is a significant and independent relationship between CT-determined tumour volume and local recurrence in moderately advanced squamous cell carcinoma of the larynx treated with conventional radiotherapy. Based on these results and those of similar studies, CT should therefore become a routine part of the staging system for T2 tumours and above.

Adult↗
PubMed1995

A pre-induction sporulation gene from Aspergillus nidulans.

Asexual sporulation in Aspergillus nidulans is an inducible developmental process controlled by genes that act before and after the inductive stimulus is applied. Genes that act before induction (pre-induction genes) potentially represent functions required for response to induction. This report describes the isolation and characterization of the acoB pre-induction gene which was cloned by complementation of a thermosensitive aconidial mutant followed by gene rescue. Genetic analysis and gene disruption confirmed the identity of the cloned gene. The mRNA of the acoB gene was present in uninduced vegetative hyphae, induced conidiating cultures and in both conidiospores and ascospores. An ORF in the nucleotide sequence of the acoB cDNA specifies a 327-residue protein unrelated to any known peptide sequence. Sequence analysis of the thermosensitive mutant allele, acoB202, revealed that the mutant phenotype is due to a frame-shift mutation that severely truncates the putative ACOB protein. Disruption of the acoB gene also produced a strain that was thermosensitive for conidiation. These properties suggest that acoB may be a gene that is required for sporulation only at elevated temperatures. Hybridization of acoB DNA with DNA from a variety of Aspergillus species showed that homology to this gene is largely restricted to sexually sporulating species that belong to the nidulans group.

Amino Acid Sequence↗