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Biomedical subjects

Yusuf Erdi

Publications and source records attributed to Yusuf Erdi.

7 recordsLinked to original sources
PubMed2005

Does registration of PET and planning CT images decrease interobserver and intraobserver variation in delineating tumor volumes for non-small-cell lung cancer?

PURPOSE: To compare tumor volume delineation using registered positron emission tomography (PET)/CT vs. side-by-side image sets. METHODS AND MATERIALS: A total of 19 patients with non-small-cell lung cancer had 18-fluorine-deoxyglucose (FDG)-PET scans registered with planning CT scans. The disease was Stage I-II in 26%, IIIA in 42%, and IIIB in 32%. Two radiation oncologists contoured 9 tumor volumes using registered images (registered) and 10 using separate FDG-PET images as a guide (nonregistered). A third physician, who had done the treatment planning for these patients a median of 40 months before using registered images, repeated all contours: 10 on registered images (registered/registered) and 9 without registration (registered/nonregistered). Each pair of volumes (A and B) was compared. Quantitative comparison used the concordance index, (A intersection B)/(A union or logical sum B). For qualitative analysis, pairs of volumes were projected onto digitally reconstructed radiographs. The differences were graded as insignificant, minor, moderate, or major. RESULTS: The median interobserver percentage of concordance among nonregistered pairs was 61% vs. 70% in the registered group (p <0.05). On qualitative analysis, in the nonregistered group, the differences were insignificant in 5, minor in 3, and moderate in 2 of 10. The differences in the registered group were insignificant in 7 and minor in 2 of 9. The median intraobserver percentage of concordance in the registered/nonregistered group was 58% vs. 71% in the registered/registered group (p = 0.10). On qualitative analysis, the intraobserver differences in the registered/nonregistered group were insignificant in 2, minor in 2, moderate in 0, and major in 5 of 9. In the registered/registered group, the differences were insignificant in 2, minor in 6, moderate in 2, and major in 0 of 10. CONCLUSION: Registration of FDG-PET and planning CT images results in greater consistency in tumor volume delineation.

Adult↗
PubMed2004

Tumor localization of 16beta-18F-fluoro-5alpha-dihydrotestosterone versus 18F-FDG in patients with progressive, metastatic prostate cancer.

UNLABELLED: This trial was an initial assessment of the feasibility, in vivo targeting, and biokinetics of 16beta-(18)F-fluoro-5alpha-dihydrotestosterone ((18)F-FDHT) PET in patients with metastatic prostate cancer to assess androgen receptor expression. METHODS: Seven patients with progressive clinically metastatic prostate cancer underwent (18)F-FDG and (18)F-FDHT PET scans in addition to conventional imaging methods. Three patients had their studies repeated 1 mo later, 2 while on testosterone therapy, and the third after treatment with 17-allylamino-17-demethoxygeldanamycin (17-AAG). High-pressure liquid radiochromatography was used to separate (18)F-FDHT from radiolabeled metabolites. Lesion-by-lesion comparisons between the (18)F-FDHT, (18)F-FDG, and conventional imaging methods were performed. RESULTS: Metabolism of (18)F-FDHT was rapid, with 80% conversion within 10 min to radiolabeled metabolites that circulated bound to plasma proteins. Tumor uptake was rapid and tumor retention was prolonged. Fifty-nine lesions were identified by conventional imaging methods. (18)F-FDG PET was positive in 57 of 59 lesions (97%), with an average lesion maximum standardized uptake value (SUV(max)) = 5.22. (18)F-FDHT PET was positive in 46 of 59 lesions (78%), with the average positive lesion SUV(max) = 5.28. Treatment with testosterone resulted in diminished (18)F-FDHT uptake at the tumor site. CONCLUSION: (18)F-FDHT localizes to tumor sites in patients with progressive clinically metastatic prostate cancer and may be a promising agent to analyze antigen receptors and their impact on the clinical management of prostate cancer.

Aged↗
PubMed2004

PET-based radiation dosimetry in man of 18F-fluorodihydrotestosterone, a new radiotracer for imaging prostate cancer.

UNLABELLED: 16 beta-fluoro-5 alpha-dihydrotestosterone (FDHT) is a promising new PET radiopharmaceutical for the imaging of prostate cancer. A recent clinical trial provided the opportunity for refinement of normal-tissue radiation-absorbed dose estimates based on quantitative PET. The objective of the current study was to derive estimates of normal-tissue absorbed doses for (18)F-FDHT administered to patients with advanced prostate cancer. METHODS: Absorbed dose estimates were derived from 10 (18)F-FDHT PET studies (administered activity, 111-407 MBq) of 7 prostate cancer patients. Activity concentrations in plasma and red marrow (assuming a plasmacrit of 0.58, an extracellular fluid fraction of 0.40, and equilibration of activity between plasma and marrow extracellular fluid) were measured ex vivo from a peripheral blood sample. Liver, spleen, urinary bladder contents, and total-body activities were measured by region-of-interest analysis of quantitative whole-body studies acquired with a dedicated PET scanner. Total organ activities and residence times were calculated from the respective PET scan-derived activity concentrations assuming standard (70 kg) man organ masses. Urinary excretion was corrected for hepatobiliary excretion (liver activity), and a first-order adjustment was made for the bladder-wall mass based on the patient's total-body mass. Mean organ absorbed doses were calculated with the MIRD formalism and the standard man model using the MIRDOSE3 software program. RESULTS: The absorbed doses (mean +/- SD) ranged from 0.00057 +/- 0.000281 cGy/MBq (to skin) to 0.00868 +/- 0.00481 cGy/MBq (to bladder wall) (voiding intervals, 1-2 h), and the effective dose equivalent was 0.00177 +/- 0.000152 cSv/MBq. CONCLUSION: The maximum absorbed dose among all tissues in all 10 studies, 0.0151 cGy/MBq, occurred for the urinary bladder wall (with hydration and 1- to 2-h voiding intervals). To ensure that the maximum normal-tissue absorbed dose is kept below the recommended maximum permissible dose of 5 cGy per single administration, a maximum administered activity of 331 MBq (5 cGy/[0.0151 cGy/MBq]) is recommended for (18)F-FDHT.

Body Burden↗
PubMed2003

Respiratory artefact causing malpositioning of liver dome lesion in right lower lung.

The new combined positron emission (PET)/computed tomographic (CT) scanners have many advantages over PET scanners alone. However, physicians must be aware of the potential artefacts observed in PET/CT scanners. A body PET/CT was performed on an 81-year-old man with colorectal cancer. The CT-based, attenuation-corrected PET image showed a right lower lung lesion. However, there was no lung lesion on the transmission CT image. Nonattenuation-corrected PET, and rod source-based, attenuation-corrected PET images demonstrated focal uptake in the dome of the liver. Dedicated CT with intravenous contrast confirmed that the lesion was in the liver dome and not in the right lower lung. The liver lesion was misplaced to the right lower lung in the CT-based, attenuation-corrected PET image because of a respiratory artefact. To overcome this respiration artefact the authors suggest a routine review of the nonattenuation-corrected PET images, particularly when evaluating liver dome and lower lung lesions.

Aged↗
PubMed1999

Tumor Treatment Response Based on Visual and Quantitative Changes in Global Tumor Glycolysis Using PET-FDG Imaging. The Visual Response Score and the Change in Total Lesion Glycolysis.

"Functional" tumor treatment response parameters have been developed to measure treatment induced biochemical changes in the entire tumor mass, using positron emission tomography (PET) and [F-18] fludeoxyglucose (FDG). These new parameters are intended to measure global changes in tumor glycolysis. The response parameters are determined by comparing the pre- and posttreatment PET-FDG images either visually from the change in image appearance in the region of the tumor, or quantitatively based on features of the calibrated digital PET image. The visually assessed parameters are expressed as a visual response score (VRS), or visual response index (VRI), as the estimated percent response of the tumor. Visual Response Score (VRS) is recorded on a 5 point response scale (0-4): 0: no response or progression; 1: 1-33%; 2: >33%-66%; 3: >66%-99%; and 4: >99%, estimated response, respectively. The quantitative changes are expressed as total lesion glycolysis TLG or as the change in TLG during treatment, also called deltaTLG or Larson-Ginsberg Index (LGI), expressed as percent response. The volume of the lesion is determined from the PET-FDG images by an adaptive thresholding technique. This response index is computed as, deltaTLG (LGI) = {[(SUV(ave))(1) * (Vol)(1) - (SUV(ave))(2) * (Vol)(2)]/[(SUV(ave))(1) * (Vol)(1)]} * 100. Where "1" and "2" denote the pre- and posttreatment PET-FDG, scans respectively. Pre- and posttreatment PET-FDG scans were performed on a group of 41 locally advanced lung (2), rectal (17), esophageal (16) and gastric (6) cancers. These patients were treated before surgery with neoadjuvant chemo-radiation. Four experienced PET readers determined individual VRS and VRI blinded to each other as well as to the clinical history. Consensus VRS was obtained based on a discussion. The interobserver variability captured by intraclass correlation coefficient was 89.7%. In addition, reader reliability was assessed for the categorized VRS using Kendall's coefficient of concordance for ordinal data and was found to be equal to 85% This provided assurance that these response parameters were highly reproducible. The correlation of deltaTLG with % change in SUV(ave) and % change in SUV(max), as widely used parameters of response, were 0.73 and 0.78 (P <.0001) respectively. The corresponding correlation of VRI were 0.63 and 0.64 (P <.0001) respectively. Both deltaTLG and VRI showed greater mean changes than SUV maximum or average (59.7% and 76% vs. 46.9% and 46.8%). We conclude that VRS and deltaTLG are substantially correlated with other response parameters and are highly reproducible. As global measures of metabolic response, VRS, VRI and deltaTLG (LGI) should provide complementary information to more commonly used PET response parameters like the metabolic rate of FDG (MRFDG), or the standardized uptake value (SUV), that are calculated as normalized per gram of tumor. These findings set the stage for validation studies of the VRS and deltaTLG as objective measures of clinical treatment response, through comparison to the appropriate gold standards of posttreatment histopathology, recurrence free survival, and disease specific survival in well characterized populations of patients with locally advanced cancers.

Journal Article↗
PubMed1999

Changes in FDG Tumor Uptake during and after Fractionated Radiation Therapy in a Rodent Tumor Xenograft.

OBJECTIVE: The uptake of FDG was measured before, during, and after fractionated radiation in order to evaluate the potential of FDG-PET imaging as an indicator of tumor response.METHODS: The study was performed with nude rats bearing the human neuroblastoma BE(2)C tumor xenografts. Tumors were irradiated with 10 fractions of 2 Gy using a 320 kV(p) X-ray unit. Following a baseline FDG-PET scan, repeat scans were performed weekly until animal sacrifice. The rodents were given up to 10 FDG-PET scans, over a period of up to 75 days posttreatment.RESULTS AND CONCLUSIONS: Neither, the average and maximum activity/cc of FDG tumor uptake, nor the respective standardized uptake values (SUV), correlated with tumor response. Instead, the total FDG uptake (defined as the product of the average FDG activity/cc with the tumor volume) correlated better with tumor response.

Journal Article↗