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Mark Phillips

Publications and source records attributed to Mark Phillips.

10 recordsLinked to original sources
PubMed2006

Tumor delineation using PET in head and neck cancers: threshold contouring and lesion volumes.

Tumor boundary delineation using positron emission tomography (PET) is a promising tool for radiation therapy applications. In this study we quantify the uncertainties in tumor boundary delineation as a function of the reconstruction method, smoothing, and lesion size in head and neck cancer patients using FDG-PET images and evaluate the dosimetric impact on radiotherapy plans. FDG-PET images were acquired for eight patients with a GE Advance PET scanner. In addition, a 20 cm diameter cylindrical phantom with six FDG-filled spheres with volumes of 1.2 to 26.5 cm3 was imaged. PET emission scans were reconstructed with the OSEM and FBP algorithms with different smoothing parameters. PET-based tumor regions were delineated using an automatic contouring function set at progressively higher threshold contour levels and the resulting volumes were calculated. CT-based tumor volumes were also contoured by a physician on coregistered PET/CT patient images. The intensity value of the threshold contour level that returns 100% of the actual volume, I(V100), was measured. We generated intensity-modulated radiotherapy (IMRT) plans for an example head and neck patient, treating 66 Gy to CT-based gross disease and 54 Gy to nodal regions at risk, followed by a boost to the FDG-PET-based tumor. The volumes of PET-based tumors are a sensitive function of threshold contour level for all patients and phantom datasets. A 5% change in threshold contour level can translate into a 200% increase in volume. Phantom data indicate that I(V100) can be set as a fraction, f, of the maximum measured uptake. Fractional threshold values in the cylindrical water phantom range from 0.23 to 0.51. Both the fractional threshold and the threshold-volume curve are dependent on lesion size, with lesions smaller than approximately 5 cm3 displaying a more pronounced sensitivity and larger fractional threshold values. The threshold-volume curves and fractional threshold values also depend on the reconstruction algorithm and smoothing filter with more smoothing requiring a higher fractional threshold contour level. The threshold contour level affects the tumor size, and therefore the ultimate boost dose that is achievable with IMRT. In an example head and neck IMRT plan, the D95 of the planning target volume decreased from 7770 to 7230 cGy for 42% vs. 55% contour threshold levels. PET-based tumor volumes are strongly affected by the choice of threshold level. This can have a significant dosimetric impact. The appropriate threshold level depends on lesion size and image reconstruction parameters. These effects should be carefully considered when using PET contour and/or volume information for radiotherapy applications.

Head and Neck Neoplasms↗
PubMed2005

FDG-PET/CT imaging for preradiotherapy staging of head-and-neck squamous cell carcinoma.

PURPOSE: Image localization of head-and-neck squamous cell carcinoma lags behind current techniques to deliver a precise radiation dose with intensity-modulated radiotherapy. This pilot study prospectively examined the use of registered 18-F-fluorodeoxyglucose (FDG)-positron emission tomography (PET)/CT for preradiotherapy staging of the neck. METHODS AND MATERIALS: Sixty-three patients with squamous cell carcinoma of the oral cavity, oropharynx, larynx, or hypopharynx were enrolled into an institutional FDG-PET imaging protocol between September 2000 and June 2003. Of these patients, 20 went on to immediate neck dissection surgery and were studied further. Of these 20, 17 (85%) had American Joint Committee on Cancer Stage III or IV disease. All patients underwent preoperative FDG-PET and contrast-enhanced CT of the head and neck. FDG-PET/CT images were created using a nonrigid image registration algorithm developed at the University of Washington. Alternate primary and nodal gross tumor volumes were contoured with radiotherapy treatment planning software, blinded to each other and to the pathology results. One set of volumes was designed with CT guidance alone and the other with the corresponding FDG-PET/CT images. Neck dissection specimens were subdivided into surgical nodal levels intraoperatively, and the histopathologic findings were correlated with the CT and FDG-PET/CT nodal level findings. RESULTS: FDG-PET/CT detected 17 of 17 heminecks and 26 of 27 nodal zones histologically positive by dissection (100% and 96% sensitivity, respectively). The nodal level staging sensitivity and specificity for FDG-PET/CT was 96% (26 of 27) and 98.5% (68 of 69), respectively. FDG-PET/CT correctly detected nodal disease in 2 patients considered to have node-negative disease by CT alone. Agreement between the imaging results and pathology findings was stronger for FDG-PET/CT (kappa 0.95, 95% confidence interval 0.82-0.99) than for CT alone (kappa 0.81, 95% confidence interval 0.63-0.91; p = 0.06 by two-sided McNemar's testing). CONCLUSION: These early findings suggest that FDG-PET/CT is superior to CT alone for geographic localization of diseased neck node levels. Confirmatory trials to substantiate the accuracy of FDG-PET/CT neck staging should be prioritized.

Adult↗
PubMed2005

FDG-PET/CT-guided intensity modulated head and neck radiotherapy: a pilot investigation.

BACKGROUND: 2-deoxy-2[(18)F]fluoro-D-glucose-positron emission tomography (FDG-PET) imaging can be registered with CT images and can potentially improve neck staging sensitivity and specificity in patients with head and neck squamous cell cancer. The intent of this study was to examine the use of registered FDG-PET/CT imaging to guide head and neck intensity modulated radiotherapy (IMRT) planning. METHODS: Twenty patients with squamous cell carcinoma of the oral cavity, oropharynx, larynx, or hypopharynx underwent FDG-PET and contrast-enhanced CT imaging of the head and neck before neck dissection surgery. Combined FDG-PET/CT images were created by use of a nonrigid image registration algorithm. All IMRT plans were theoretical and were not used for treatment. We prescribed 66 Gy in 30 fractions to FDG-avid CT abnormalities and nodal zones directly involved with disease, without prophylactic coverage of uninvolved neck levels. Matched CT-guided IMRT plans designed according to the specifications of Radiation Therapy Oncology Group (RTOG) H-0022 were available for comparison. We investigated the feasibility of FDG-PET/CT-directed IMRT dose escalation in five patients with FDG-avid disease located away from critical normal structures. After 66 Gy, FDG-avid disease with 0.5-cm margins was boosted in 220 cGy increments until dose-limiting criteria were reached. RESULTS: Elimination of prophylactic coverage to FDG-PET/CT-negative neck levels markedly reduced mean dose (Dmean) to the contralateral parotid gland (p < .001) and Dmean to the laryngeal cartilage (p = .001). No FDG-PET/CT-directed plan missed pathologically verified nodal disease. During the dose escalation exercise, we successfully increased the dose to 95% of the planning target volume (PTV95%) to a mean of 7490 cGy (range, 7153-8098 cGy). CONCLUSIONS: We demonstrate early proof of the principle that FDG-PET/CT-guided IMRT planning can selectively target and intensify treatment of head and neck disease while reducing critical normal tissue doses. Routine clinical use of such planning should not be engaged until the accuracy of FDG-PET/CT is fully validated. Future directions, including refinement of treatment to gross disease and radiologically uninvolved neck nodal levels, are discussed.

Adult↗
PubMed2005

AFLP analysis of the genetic diversity of Meloidogyne chitwoodi and M. fallax, major agricultural pests.

M. chitwoodi and M. fallax populations are clustered and separated from the other species studied. The genetic diversity observed for M. incognita, M. arenaria, M. javanica, M. hapla, and M. mayaguensis correlates well with the previously validated species. Two main groups can be identified within the M. chitwoodi/M. fallax cluster, the first group comprises only M. chitwoodi populations whereas the second group is made of M. chitwoodi and M. fallax populations. Moreover, M. chitwoodi displays a higher genetic diversity than M. fallax and is characterised by the presence of several clusters.

Animals↗
PubMed2005

Epidemiology of trauma in Minnesota.

Injury accounts for more than 2,500 deaths and 300,000 hospital admissions in Minnesota each year. Using the 2002 Minnesota hospital discharge database, we examined the subset of hospital-treated injuries that received trauma care and categorized claims into trauma-related deaths, cases of nonfatal major trauma, and other cases that received specialized trauma care. We also examined where trauma patients received their care, the leading diagnoses for trauma deaths and nonfatal major trauma, and whether a statewide trauma system that would identify and equip more hospitals as trauma centers would have significant potential for improving trauma care in Minnesota.

Cross-Sectional Studies↗
PubMed2003

Soil community composition and the regulation of grazed temperate grassland.

The effect of the community composition of soil microbes on ecosystem processes has received relatively little attention. Here we examined the variation in soil microbial composition in a Yellowstone National Park grassland and the effect of that variation on the growth, in a greenhouse, of the dominant grass in the community. Plants and their rhizospheric soil were collected from paired, Poa pratensis-dominated grassland plots located inside and outside a 40-year-old exclosure. P. pratensis aboveground, belowground, and whole plant growth were greater in pots with soil communities from grazed grassland compared to fenced grassland, indicating (1) soil microbial communities differed, and (2) this difference influenced the growth of the plant that dominated both grasslands. Treating pots with fungicide (benomyl) suppressed the soil community influence, indicating that different fungal communities caused the soil microbe effect. In addition, two lines of evidence are consistent with the hypothesis that arbuscular mycorrhizal fungal (AMF) species composition affected P. pratensis: (1) a divergence in AMF spore communities in the two field soils, and (2) little evidence of pathogenic fungi. These findings emphasize the need to examine the role that the composition of the soil microbial community plays in controlling terrestrial ecosystems.

Climate↗
PubMed2002

Spin coherence and electromagnetically induced transparency via exciton correlations.

We report experimental studies on exciton spin coherence induced via Coulomb correlations between excitons with opposite spins, including correlations associated with unbound as well as bound exciton pairs. Electromagnetically induced transparency resulting from the spin coherence is demonstrated in the transient optical response in GaAs quantum wells.

Journal Article↗
PubMed2002

Effects of management on the yield and high-molecular-weight polysaccharide content of shiitake (Lentinula edodes) mushrooms.

Shiitake (Lentinula edodes (Berk.) Pegler) mushroom production in the United States has increased greatly over the last twenty years. Additional expansion of the shiitake mushroom market should be possible if the product can be marketed as a functional food, i.e., a food that has health-promoting effects beyond its nutritional value. High-molecular-weight polysaccharides (HMWP) including lentinan in shiitake may promote human health. This study was conducted to determine if management protocols influence the HMWP of shiitake mushrooms. Results indicate that measuring the total carbohydrate content of water-extractable, ethanol-insoluble polysaccharides was a simple way to estimate HMWP. Results also indicate that log-grown shiitake contained more HMWP than did substrate-grown shiitake. Among log-grown shiitake, both mushroom strain and tree species influenced HMWP content. The results suggest that there is considerable variation among shiitake mushrooms in HMWP content and that production protocols influenced the HMWP content of mushrooms.

Agriculture↗