Adaptive Dose Escalation using Serial Four-dimensional Positron Emission Tomography/Computed Tomography Scans during Radiotherapy for Locally Advanced Non-small Cell Lung Cancer.

AIMS: Computed tomography (CT)-based radiotherapy dose escalation for locally advanced non-small cell lung cancer (LA-NSCLC) has had limited success. In this planning study, we investigated the potential for adaptive dose escalation using respiratory-gated 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography scans (4DPET/4DCT) acquired before and during a course of chemoradiotherapy (CRT). MATERIALS AND METHODS: We prospectively enrolled patients with LA-NSCLC receiving curative intent CRT. Radiotherapy was delivered using intensity-modulated radiotherapy (IMRT) using the week 0 4DCT scan. Three alternative, dose-escalated IMRT plans were developed offline based on the week 0, 2 and 4 4DPET/4DCT scans. The FDG-avid primary (PET-T) and nodal disease (PET-N) volumes defined by the 50% of maximum standard uptake value threshold were dose escalated to as high as possible while respecting organ at risk constraints. RESULTS: Thirty-two patients were recruited, 27 completing all scans. Twenty-five patients (93%) were boosted successfully above the clinical plan doses at week 0, 23 (85%) at week 2 and 20 (74%) at week 4. The median dose received by 95% of the planning target volume (D95) at week 0, 2 and 4 to PET-T were 74.4 Gy, 75.3 Gy and 74.1 Gy and to PET-N were 74.3 Gy, 71.0 Gy and 69.5 Gy. CONCLUSIONS: Using 18F-FDG-4DPET/4DCT, it is feasible to dose escalate both primary and nodal disease in most patients. Choosing week 0 images to plan a course with an integrated boost to PET-avid disease allows for more patients to be successfully dose escalated with the highest boost dose.

Radiation dosimetry estimates for the PET serotonin transporter probe 11C-DASB determined from whole-body imaging in non-human primates.

The radiotracer 3-amino-4-(2-dimethylaminomethyl-phenylsulfanyl)-benzonitrile labelled in the N-methyl position (11C-DASB) is a selective radioligand for the in vivo quantification of serotonin transporters (SERTs) using positron emission tomography (PET). The current study quantified the distribution of activity in two rhesus monkeys after the injection of approximately 333 MBq (9 mCi) 11C-DASB. Whole-body images were acquired at 22 time points for a total of 120 min following injection of the radioligand. Source organs were identified at each time point from both tomographic images (using multiple regions of interest on each tomograph for each organ) and a single planar image (using a single region of interest for each organ). The peak activities in planar images in the five identified source organs (expressed as per cent injected dose (ID)) were lungs (24% ID at 1.5 min), kidneys (6.5% ID at 4 min), liver (8% ID at 3 min), brain (4% ID at 5 min) and spleen (0.42% ID at 3 min). Mono-exponential fitting of activity overlying the bladder suggested that approximately 14% of activity was excreted via the urine. The radiation burden to the body was calculated from residence times of these source organs and then scaled to corresponding human values. The calculated effective dose from tomographic and planar images was 6.0 and 6.4 microGy x MBq(-1) (22.3 and 23.7 mrad x mCi(-1)), respectively. The planar analysis was much easier to perform, and generally yielded slightly higher (i.e., more conservative) estimates of radiation burden than the tomographic analysis. The estimated radiation burden of 11C-DASB is relatively modest and would allow multiple scans per research subject per year.

Receptor-mediated regulation of plasminogen activator function: plasminogen activation by two directly membrane-anchored forms of urokinase.

The generation of the broad specificity serine protease plasmin in the pericellular environment is regulated by binding of the urokinase-type plasminogen activator (uPA) to its specific glycosylphosphatidylinositol (GPI)-anchored cell-surface receptor, uPAR. This interaction potentiates the reciprocal activation of the cell-associated zymogens pro-uPA and plasminogen. To further study the role of uPAR in this mechanism, we have expressed two directly membrane-anchored chimeric forms of uPA, one anchored by a C-terminal GPI-moiety (GPI-uPA), the other with a C-terminal transmembrane peptide (TM-uPA). These were expressed in the monocyte-like cell lines U937 and THP-1, which are excellent models for kinetic and mechanistic studies of cell-surface plasminogen activation. In both cell-lines, GPI-uPA activated cell-associated plasminogen with characteristics both qualitatively and quantitatively indistinguishable from those of uPAR-bound uPA. By contrast, TM-uPA activated cell-associated plasminogen less efficiently. This was due to effects on the K, for plasminogen activation (which was increased up to five-fold) and the efficiency of pro-uPA activation (which was decreased approximately four-fold). These observations suggest that uPAR serves two essential roles in mediating efficient cell-surface plasminogen activation. In addition to confining uPA to the cell-surface, the GPI-anchor plays an important role by increasing accessibility to substrate plasminogen and, thus, enhancing catalysis. However, the data also demonstrate that, in the presence of an alternative mechanism for uPA localization, uPAR is dispensable and, therefore, unlikely to participate in any additional interactions that may be necessary for the efficiency of this proteolytic system. In these experiments zymogen pro-uPA was unexpectedly found to be constitutively activated when expressed in THP-1 cells, suggesting the presence of an alternative plasmin-independent proteolytic activation mechanism in these cells.

Normal patterns on 99mTc-ECD brain SPECT scans in adults.

UNLABELLED: Normative ethyl cysteinate dimer (ECD) SPECT data must be available to successfully apply ECD SPECT to clinical studies. The purpose of this study was to determine ECD SPECT scan patterns of healthy adults. METHODS: Forty-eight healthy volunteers (22 men, 26 women; age range, 22-95 y; mean age, 47.6 +/- 19.2 y) underwent high-resolution ECD SPECT. For visual analysis of regional brain ECD uptake, we used a scale of +3 to -3, in which +3 and -3 indicated highest ECD uptake and deficit, respectively. For quantitative analysis, we measured the region-to-cerebellum ratio (R/CE) and the region-to-cerebral cortex ratio (R/CO) for 17 regions (13 cortical, 3 subcortical, and 1 cerebellar). RESULTS: On visual analysis, no subject had a score of -3. All subjects had a score of -2 for the hippocampus and a score of +3 for the medial occipital cortex, except for 2 subjects who had a score of +3 for the striatum and thalamus. A frontal eye field and posterior parieto-occipital junction were identified in 60% of subjects with a score of +1 and 79% of subjects with a score of +2. On quantitative analysis, a significant regional variation (ANOVA, P < 0.0001) was seen in R/CE, ranging from 0.709 (hippocampus) to 1.26 (medial occipital cortex). However, regional right-to-left differences and intersubject variability of R/CE were small (asymmetry index, 3.6% +/- 0.8%; coefficient variation, 6.6% +/- 0.7%). R/CE declined significantly with age in 6 regions, including the anterior and posterior cingulate cortex, superior prefrontal and parietal cortex, striatum, and hippocampus (1.0%-2.0% per decade, P < 0.05), whereas R/CO in the cerebellum increased significantly with age (1.0% per decade, P < 0.05). CONCLUSION: Although regional ECD brain perfusion patterns vary significantly, including variability caused by the age-related effect, intersubject variability is small. Recognition of these normal patterns is important for clinical interpretation of ECD SPECT studies.

Evaluation of differential magnification during brain SPECT acquisition.

OBJECTIVE: We developed a modification of the acquisition zoom technique, referred to as differential magnification (DM), to improve the pixel resolution with fanbeam collimators. This study evaluated the effects of DM on brain SPECT image quality. METHODS: SPECT imaging was performed using a triple-head camera with and without DM for a line source in air, Jaszczak and Hoffman phantoms, and 15 clinical patients having regional cerebral blood-flow scans with 99mTc ECD. Full width at half maximum (FWHM) and contrast ratios were measured on the line source and Jaszczak phantom data, respectively. Visual image evaluation was performed by 2 independent, blinded observers for the Hoffman brain phantom images and clinical patient studies. RESULTS: FWHM improved on the fanned axis (transverse plane) by 0.05 mm (P < 0.001), and the unfanned axis (longitudinal plane) by 0.66 mm (P < 10(-6)), when DM was used. The mean improvement of contrast ratios for the spheres on the Jaszczak phantom with DM was 11.4% (P < 0.004). The images with DM were rated superior to those without, for the Hoffman brain phantom and the clinical patients. CONCLUSION: This study has demonstrated that SPECT acquisition with fanbeam collimators and DM significantly improves both FWHM and image contrast, resulting in superior image quality. DM techniques may be useful in improving clinical brain SPECT images.

External radioactive reference markers in SPECT imaging of the dopamine system.

OBJECTIVE: External radioactive reference markers have been used to localize the canthomeatal (CM) line and correct for head rotation in perfusion brain SPECT. This ensures that regardless of the subject's head position or rotation under the SPECT camera, reconstructed transaxial slices are reoriented parallel to the CM line. This study was undertaken to demonstrate the value of external radioactive reference markers in dopamine SPECT imaging. METHODS: We compared visual and marker methods of reorienting the transaxial slices between dopamine and perfusion brain SPECT studies, respectively. These consisted of imaging normal controls and patients with Alzheimer's or Parkinson's disease using a triple-head camera. Intra- and interoperator variability of the visual and marker methods of reorientation was determined for both perfusion and dopamine studies. RESULTS: In both intra- and interoperator studies, the variability of image reorientation was significantly reduced (P = 0.0066 and 0.014, respectively) by using the marker method on dopamine images. The variability of reorientation using the marker method for a single operator with dopamine images was 3.0% coefficient of variation (CV), and for the interoperator study (5 different operators) this was 7.0% CV. CONCLUSION: This study demonstrated that SPECT imaging of the dopamine system with external radioactive reference markers significantly reduced the variability of determining the angle of reorientation. This resulted in a standardized and consistent method of reorienting transaxial slices, allowing comparison within and between subjects of pre- and postsynaptic dopamine SPECT studies.

SPECT imaging of pre- and postsynaptic dopaminergic alterations in L-dopa-untreated PD.

BACKGROUND: In PD, presynaptic dopamine transporters are known to be decreased, whereas postsynaptic striatal D2 receptors are proposed to be upregulated. However, the relationship between these alterations is not clear. OBJECTIVE: To evaluate the ability of SPECT to detect both the pre- and postsynaptic dopaminergic alterations of the striatum in patients with L-dopa-untreated PD. METHODS: We studied 10 L-dopa-untreated patients with clinically mild PD and 21 age-matched normal controls. Individuals had both presynaptic [123I]beta-CIT dopamine transporter and postsynaptic [123I]IBF D2 SPECT studies 1 week apart. RESULTS: In PD patients, the dopamine transporter binding potential Rv ipsilateral/contralateral to the most affected limbs was 30%/41%, 41%/50%, and 59%/68% lower than controls for caudate, anterior putamen, and posterior putamen, respectively. These bilateral Rv decreases showed a lateralized difference more reduced in the contralateral striatum as well as intrastriatal differences most reduced in the posterior putamen. In contrast, in PD patients the D2 binding potential Rv ipsilateral/contralateral was 15%/16% higher for caudate, 18%/14% higher for anterior putamen, and 28%/31% higher for posterior putamen. These bilateral Rv increases showed no lateralized differences and less marked intrastriatal differences. The motor Unified Parkinson's Disease Rating Scale scores negatively correlated with dopamine transporter Rv but not with D2 Rv. CONCLUSIONS: SPECT imaging can detect characteristic dopaminergic alterations in the striatum of dopa-untreated PD patients including the upregulation of postsynaptic D2 receptors (denervation supersensitivity). SPECT is widely available and is a promising clinical tool to evaluate PD patients.

Functional morphometry of the striatum in Parkinson's disease on three-dimensional surface display of 123I-beta-CIT SPECT data.

UNLABELLED: The purpose of this study was to evaluate whether striatal morphology on a three-dimensional surface display of 123I-2beta-carbomethoxy-3beta-(4-iodophenyl)tropane (123I-beta-CIT) SPECT data can be used as a diagnostic index for Parkinson's disease. METHODS: We studied 11 patients with mild Parkinson's disease and 21 age-matched controls. Triple-head SPECT scans were acquired for 30 min at 20 h after injection of 123I-beta-CIT. We measured the vertical height of the caudate head (H) and the length of the long axis of the striatum (L) on the three-dimensional surface display generated from SPECT data. The morphometric index of the striatum was defined as L/H. The power of L/H to discriminate Parkinson's disease and control groups was evaluated by discriminant function analysis and was compared with that of region of interest (ROI)-based 123I-beta-CIT binding measurements (V"3) and their ratios. RESULTS: The mean L/H ratios (ipsilateral/contralateral) to the most affected limbs were (33%/45%) lower in the Parkinson's disease group compared with the control group, respectively. All other ROI-based measures confirmed that dopamine transporter reductions were most severe in the contralateral posterior putamen (a 68% reduction in V"3). In 1 patient with a subsequent clinical diagnosis of drug-induced parkinsonism, all SPECT measures were normal. The contralateral putamen contributed most to the discriminatory power, and the contralateral L/H showed the best discriminatory power of all SPECT measures. CONCLUSION: These results suggest that striatal morphology on a three-dimensional display of 123I-beta-CIT SPECT data provides information of diagnostic significance for Parkinson's disease. This morphometry can be done without requiring technically demanding ROI analysis, and thus this technique may be suitable for routine clinical use.

Classical late infantile neuronal ceroid lipofuscinosis fibroblasts are deficient in lysosomal tripeptidyl peptidase I.

Tripeptidyl peptidase I (TPP-I) is a lysosomal enzyme that cleaves tripeptides from the N-terminus of polypeptides. A comparison of TPP-I amino acid sequences with sequences derived from an EST database suggested that TPP-I is identical to a pepstatin-insensitive carboxyl proteinase of unknown specificity which is mutated in classical late infantile neuronal ceroid lipofuscinosis (LINCL), a lysosomal storage disease. Both TPP-I and the carboxyl proteinase have an M(r) of about 46 kDa and are, or are predicted to be, resistant to inhibitors of the four major classes of proteinases. Fibroblasts from LINCL patients have less than 5% of the normal TPP-I activity. The activities of other lysosomal enzymes, including proteinases, are in the normal range. LINCL fibroblasts are also defective at degrading short polypeptides and this defect can be induced in normal fibroblasts by treatment with a specific inhibitor or TPP-I. These results suggest that the cell damage, especially neuronal, observed in LINCL results from the defective degradation and consequent lysosomal storage of small peptides.

Purification and characterisation of a tripeptidyl aminopeptidase I from rat spleen.

A tripeptidyl aminopeptidase I with an M(r) of 47,000 Da has been purified from rat spleen. The N-terminal sequence of the enzyme and internal sequences did not resemble that of any known protein. The enzyme cleaves tripeptides from synthetic substrates provided that the N-terminus is unsubstituted and the amino acid in the P1 position is not charged. The enzyme also cleaves small peptides (angiotensin II and glucagon) releasing tripeptides but does not appear to demonstrate any preference for amino acids on either side of the cleavage site. The enzyme had maximum activity at pH 4 but was unstable above pH 7. Rat spleen tripeptidyl peptidase I was not inhibited by classical inhibitors of serine, cysteine, aspartate or metalloproteinases. The peptidase was potently inhibited by a series of substrate-based tripeptidyl chloromethyl ketones (Ki's of 10(-6)-10(-8) M). Inhibition was rapid and reversible. This mode of inhibition is different to the interaction between chloromethyl ketones and cysteine or serine peptidases. These tripeptidyl chloromethyl ketones were also inhibitors of bone resorption using an in vitro assay suggesting that a tripeptidyl peptidase is involved in the degradation of bone matrix proteins.

Off-site determinations of effective renal plasma flow using technetium-99m-MAG3 and single blood sampling.

UNLABELLED: This study evaluated the feasibility of determining effective renal plasma flow (ERPF) at an off-site central laboratory by transferring blood samples from the on-site laboratory. METHODS: Blood samples were obtained from 66 patients referred for renal imaging with 99mTc-MAG3. ERPF values were determined using the single blood sample method (BSM) at both on- and off-site laboratories. The ERPF values were classified clinically as normal or abnormal. Both the ERPF values and clinical classification were compared between on- and off-site laboratories. RESULTS: The off-site ERPF overestimated those on-site by 2.8% (paired Student's t-test p < 10(-5)). However, off-site ERPF values highly correlated with the values obtained on-site (r = 0.99; p < 10(-5)). In addition, the clinical classification for each patient determined at each site was identical. CONCLUSION: ERPF can be determined accurately off-site. This method should allow many nuclear medicine departments access to the ERPF determination by the BSM at a central off-site laboratory.

Regional differences in technetium-99m-ECD clearance on brain SPECT in healthy subjects.

UNLABELLED: The aim of this study was to evaluate the in vivo stability of ECD brain SPECT. METHODS: Twenty normal volunteers (35.4 +/- 9.1 yr) each had six ECD scans at 30, 60, 120, 240, 360 and 480 min postinjection. Each scan was acquired for 24 min using a triple-head SPECT system. Average counts per pixel were measured from frontal, temporal, parietal, occipital, cerebellum, basal ganglia, thalamus and white matter regions. ECD clearance rates were calculated by fitting regional time activity data to a monoexponential equation. Regional gray-to-white matter (G/W) and gray-to-cerebellum (G/C) ratios were calculated for each scan. Analysis of variance was used to compare regional ECD clearance and ratio measurements. RESULTS: The average ECD clearance was 4.3%/hr. There was a significant regional variation in the ECD clearance, being higher for occipital (6.34%/hr) but lower for both white matter (2.39%/hr) and thalamus (2.45%/hr). Both G/W and G/C ratios showed a significant regional variation with time. The overall G/W ratio was 2.13 at 30 min and became progressively lower after 2 hr, reaching 1.78 at 8 hr. All regional G/W ratios declined with time except for thalamus where it remained constant at 2.15. The overall G/C ratio was 0.984 at 30 min but it declined after 4 hr, reaching 0.955 at 8 hr. All regional G/C ratios declined with time except for thalamus where it increased progressively from 0.955 to 1.120 at 8 hr. CONCLUSION: ECD clears from normal brain slowly and shows a significant regional variation. As a result, G/W contrast begins to decrease after 2 hr and the gray-matter activity pattern becomes significantly different after 4 hr. Therefore, the optimal imaging time may be between 30-120 min. However, images obtained up to 4 hr still maintain the initial gray-matter activity pattern.

Simplified quantification and reproducibility studies of dopamine D2-receptor binding with iodine-123-IBF SPECT in healthy subjects.

UNLABELLED: The purpose of this study was to assess the feasibility of a simplified SPECT scan protocol to quantify D2-receptor binding using [123I]iodobenzofuran (IBF) and to evaluate reproducibility of quantitative IBF-SPECT imaging without blood data. METHODS: Twenty healthy volunteers participated in the study, six had test/retest studies separated by 1 wk. Scans were acquired every 5 min for 180 min using a triple-headed SPECT camera after a bolus injection of IBF (292 MBq). The receptor parameter was determined by using our previously proposed variation of graphical analysis that derives the distribution volume ratio (Rv = V3/V2) from multiple scan data without blood data. Rv' was determined from three 20-min scan data obtained at 0-20, 50-70 and 160-180 min postinjection and compared with Rv as determined from scans obtained at 0-180 min. RESULTS: The mean Rv' (2.93 +/- 0.59) underestimated the mean Rv (3.10 +/- 0.50) by 5%. The mean variability (mean percent absolute difference) between Rv' and Rv was low (10%) with excellent reliability (intraclass correlation coefficient, p = 0.90). The relationship between Rv' and Rv was linear (r = 0.95, p < 10(-5)). The mean test/retest Rv and mean test/retest Rv' were (3.19 +/- 0.70/3.18 +/- 0.80) and (3.16 +/- 0.81/3.01 +/- 0.94), respectively, and these measures were not significantly different between test/retest studies. The mean test/retest variability of Rv was low (5%) with excellent reliability (p = 0.98). In addition, the mean test/retest variability of Rv' was low (10%) with excellent reliability (p = 0.94). CONCLUSION: Three short (20 min) IBF-SPECT scans allowing for rest periods between scans permit reliable measurements of the dopamine D2-receptor parameter V3/V2. Quantitative IBF-SPECT imaging without blood data is reliable and reproducible.

Noninvasive quantification of dopamine D2 receptors with iodine-123-IBF SPECT.

UNLABELLED: Iodine-123-iodobenzofuran (IBF) is a potent dopamine D2 receptor ligand suited for quantitative receptor studies. The purpose of this study was to evaluate three noninvasive methods of estimating the receptor parameter k3/k4 in humans with IBF-SPECT. METHODS: Scans were acquired every 5 min for 180 min using a triple-headed SPECT system following a bolus injection of IBF (296 +/- 37 MBq) in 14 normal volunteers. k3/k4 was estimated by the peak equilibrium ratio (RPE) method and two proposed methods: a variation of the graphic method that derives the ratio of ligand distribution volumes (RV) and area ratio (RA) method, in which the ratio is calculated from the areas under the specific binding and nondisplaceable activity curves. RESULTS: The mean RPE, RV and RA were 2.74 +/- 0.40, 3.06 +/- 0.42 and 2.26 +/- 0.28, respectively. Both RPE and RA underestimated RV. The relationship between RPE or RA and RV was linear (p < or = 10(-5), RA showed higher correlation (r = 0.94) with RV than did RPE (r = 0.90). Simulations based on a tracer kinetic model showed that RV, unlike RPE or RA, is affected by neither regional cerebral blood flow (rCBF) nor peripheral clearance rate (CR) of IBF. All three measures showed a significant decline with increasing age (r = 0.54-0.58, p < 0.05). CONCLUSION: RV is preferred because it provides a theoretically valid estimate of k3/k4, independently of rCBF or CR. Alternatively, RA might be preferred to RPE because the former is simpler than the latter to implement yet the former provides a measure that equally well correlates with k3/k4.

Neuroanatomical localization for clinical SPECT perfusion brain imaging: a practical proportional grid method.

For the purpose of facilitating anatomical localization in interpretation of 99Tcm-hexamethylpropyleneamine oxime (HMPAO) brain single photon emission tomographic (SPECT) scans, a stereotaxic proportional grid system was applied in the form of an interactive computer program. This method takes advantage of a rotating gamma camera system which permits planar scout imaging for the determination of anatomical reference lines, and standardization of tomographic slices for brain size. Using measurements made on a lateral planar HMPAO image, proportional grids were constructed onto standardized transaxial images. This method was implemented for 33 clinical HMPAO SPECT studies. It required less than 15 min of an operator's time. This simple and practical neuroanatomical localization technique can be instrumental as an aid to the interpretation of routine clinical HMPAO SPECT images.