Comparison of subcutaneous and intraperitoneal injection of <Emphasis Type="SmallCaps">d</Emphasis>-luciferin for in vivo bioluminescence imaging

Purpose  We compared subcutaneous (SC) injection and intraperitoneal (IP) injection of d-luciferin for in vivo bioluminescence imaging (BLI) to determine the utility of SC injection. Methods  Mice bearing SC tumours stably expressing firefly luciferase underwent in vivo BLI using SC and IP injection of d-luciferin. BLI studies were repeated at an interval of 3 h using a given injection route to assess repeatability and using different injection routes to assess correlation. In mice bearing both SC and IP tumours, BLI was performed successively using intravenous (IV), SC, and IP injection of d-luciferin. Haematological malignancy model mice underwent BLI using SC and IP injection. Results  In SC tumours, the peak time was slightly shorter and the peak signal was greater using SC injection than using IP injection. The repeatability of determining peak signals was comparable between the two injection routes, and a good correlation was observed between them. In mice bearing both SC and IP tumours, signals from IP tumours relative to those from SC tumours were much greater using IP injection than using IV or SC injection. In the haematological malignancy model, signals from the spleen relative to those from the bone marrow were greater using IP injection than using SC injection. Conclusion  In addition to rare injection failure, the IP injection of d-luciferin led to the overestimation of signals from IP tissues. For BLI, SC injection was shown to be a convenient alternative to IP injection.     

Uptake kinetics and biodistribution of <Superscript>14</Superscript>C-<Emphasis Type="SmallCaps">d</Emphasis>-luciferin—a radiolabeled substrate for the firefly luciferase catalyzed bioluminescence reaction: impact on bioluminescence based reporter gene imaging

Purpose  Firefly luciferase catalyzes the oxidative decarboxylation of d-luciferin to oxyluciferin in the presence of cofactors, producing bioluminescence. This reaction is used in optical bioluminescence-based molecular imaging approaches to detect the expression of the firefly luciferase reporter gene. Biokinetics and distribution of the substrate most likely have a significant impact on levels of light signal and therefore need to be investigated. Methods  Benzene ring ¹⁴C(U)-labeled d-luciferin was utilized. Cell uptake and efflux assays, murine biodistribution, autoradiography and CCD-camera based optical bioluminescence imaging were carried out to examine the in vitro and in vivo characteristics of the tracer in cell culture and in living mice respectively. Results  Radiolabeled and unlabeled d-luciferin revealed comparable levels of light emission when incubated with equivalent amounts of the firefly luciferase enzyme. Cell uptake assays in pCMV-luciferase-transfected cells showed slow trapping of the tracer and relatively low uptake values (up to 22.9-fold higher in firefly luciferase gene-transfected vs. nontransfected cells, p = 0.0002). Biodistribution studies in living mice after tail-vein injection of ¹⁴C-d-luciferin demonstrated inhomogeneous tracer distribution with early predominant high radioactivity levels in kidneys (10.6% injected dose [ID]/g) and liver (11.9% ID/g), followed at later time points by the bladder (up to 81.3% ID/g) and small intestine (6.5% ID/g), reflecting the elimination routes of the tracer. Kinetics and uptake levels profoundly differed when using alternate injection routes (intravenous versus intraperitoneal). No clear trapping of ¹⁴C-d-luciferin in firefly luciferase-expressing tissues could be observed in vivo. Conclusions  The data obtained with ¹⁴C-d-luciferin provide insights into the dynamics of d-luciferin cell uptake, intracellular accumulation, and efflux. Results of the biodistribution and autoradiographic studies should be useful for optimizing and adapting optical imaging protocols to specific experimental settings when utilizing the firefly luciferase and d-luciferin system. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Non-invasive visualisation of the development of peritoneal carcinomatosis and tumour regression after <Superscript>213</Superscript>Bi-radioimmunotherapy using bioluminescence imaging

Purpose Non-invasive imaging of tumour development remains a challenge, especially for tumours in the intraperitoneal cavity. Therefore, the aim of this study was the visualisation of both the development of peritoneal carcinomatosis and tumour regression after radioimmunotherapy with tumour-specific ²¹³Bi-Immunoconjugates, via in vivo bioluminescence imaging of firefly luciferase-transfected cells. Methods Human diffuse-type gastric cancer cells expressing mutant d9-E-cadherin were stably transfected with firefly luciferase (HSC45-M2-luc). For bioluminescence imaging, nude mice were inoculated intraperitoneally with 1 × 10⁷ HSC45-M2-luc cells. On days 4 and 8 after tumour cell inoculation, imaging was performed following D-luciferin injection using a cooled CCD camera with an image intensifier unit. For therapy, mice were injected with 2.7 MBq ²¹³Bi-d9MAb targeting d9-E-cadherin on day 8 after tumour cell inoculation. Bioluminescence images were taken every 4 days to monitor tumour development. Results After i.p. inoculation of HSC45-M2-luc cells into nude mice, development as well as localisation of peritoneal carcinomatosis could be visualised using bioluminescence imaging. Following ²¹³Bi-d9MAb therapy on day 8 after intraperitoneal inoculation of HSC45-M2-luc cells, small tumour nodules were totally eliminated and larger nodules showed a clear reduction in size on day 12 after tumour cell inoculation. Subsequently a recurrence of tumour mass was observed, starting from the remaining tumour spots. By measuring the mean grey level intensity, tumour development over time could be demonstrated. Conclusion Non-invasive bioluminescence imaging permits visualisation of the development of peritoneal carcinomatosis, localisation of tumour in the intraperitoneal cavity and evaluation of therapeutic success after ²¹³Bi-d9MAb treatment.     

In vivo fluorescence imaging of the reticuloendothelial system using quantum dots in combination with bioluminescent tumour monitoring

Purpose We characterised in vivo fluorescence imaging (FLI) of the reticuloendothelial system using quantum dots (QD) and investigated its use in combination with in vivo bioluminescence imaging (BLI). Materials and methods In vivo FLI was performed in five mice repeatedly after the intravenous administration of QD without conjugation to targeting ligands. Ex vivo FLI of the excised organs was performed 24 h after QD injection in three mice. Seven days after intravenous inoculation of luciferase-expressing model cells of a haematological malignancy, mice were injected with the QD or saline (n = 5 each), and combined BLI/FLI was performed repeatedly. Additional five mice inoculated with the tumour cells were examined by in vivo BLI/FLI, and the structures harbouring bioluminescent foci were determined by ex vivo BLI. The utility of combining FLI with bioluminescent tumour monitoring was evaluated. Results In vivo FLI after QD injection allowed long-term, repeated observation of the reticuloendothelial system in individual mice, although fluorescence intensity and image contrast gradually decreased over time. Ex vivo FLI verified selective accumulation in reticuloendothelial structures. The administration of QD did not affect whole-body bioluminescent signal intensities during longitudinal tumour monitoring. In vivo BLI/FLI, accompanied by fusion of both images, improved the accuracy and confidence level of the localisation of the bioluminescent foci. Conclusions In vivo FLI using QD provides an overview of the reticuloendothelial system in living mice. In combination with bioluminescent tumour monitoring, fluorescent reticuloendothelial imaging is expected to provide valuable information for lesion localisation.     

FET PET for the evaluation of untreated gliomas: correlation of FET uptake and uptake kinetics with tumour grading

Purpose Treatment and prognosis of gliomas depend on their histological tumour grade. The aim of the study was to evaluate the potential of [¹⁸F]fluoroethyltyrosine (FET) PET for non-invasive tumour grading in untreated patients. Methods Dynamic FET PET studies were performed in 54 patients who, based on MRI, were estimated to have low grade (LG; n = 20), intermediate (WHO II–III; n = 4) or high grade (HG; n = 30) tumours. For standard evaluation, tumour SUV_max and the ratio to background (SUV_max/BG) were calculated (sum image: 20–40 min). For dynamic evaluation, mean SUV values within a 90% isocontour ROI (SUV90) and the SUV90/BG ratios were determined for each time frame to evaluate the course of FET uptake. Results were correlated with histopathological findings from PET-guided stereotactic biopsies. Results Histology revealed gliomas in all patients. Using the standard method a statistically significant difference (p = 0.001) was found between LG (n = 20; SUV_max/BG: 2.16 ± 0.98) and HG (n = 34; SUV_max/BG: 3.29 ± 1.06) gliomas (opt. threshold 2.58: SN71%/SP85%/area under ROC curve [AUC]:0.798), however, with a marked overlap between WHO II to IV tumours. Time activity curves showed slight increase in LG, whereas HG tumours presented with an early peak (10–20 min) followed by a decrease. Dynamic evaluation successfully separated LG from HG gliomas with higher diagnostic accuracy (SN94%/SP100%/AUC:0.967). Conclusions Based on the ratio-based method, a statistically significant difference was found between LG and HG gliomas. Due to the interindividual variability, however, no reliable individual grading was possible. In contrast, dynamic evaluation allowed LG and HG gliomas to be differentiated with high diagnostic power and, thus, should supplement the conventional method.     

<Superscript>11</Superscript>C-methionine (MET) and <Superscript>18</Superscript>F-fluorothymidine (FLT) PET in patients with newly diagnosed glioma

Purpose  The purpose of this prospective study was to clarify the individual and combined role of l-methyl-¹¹C-methionine-positron emission tomography (MET-PET) and 3′-deoxy-3′-[¹⁸F]fluorothymidine (FLT)-PET in tumor detection, noninvasive grading, and assessment of the cellular proliferation rate in newly diagnosed histologically verified gliomas of different grades. Materials and methods  Forty-one patients with newly diagnosed gliomas were investigated with MET-PET before surgery. Eighteen patients were also examined with FLT-PET. MET and FLT uptakes were assessed by standardized uptake value of the tumor showing the maximum uptake (SUV_max), and the ratio to uptake in the normal brain parenchyma (T/N ratio). All tumors were graded by the WHO grading system using surgical specimens, and the proliferation activity of the tumors were determined by measuring the Ki-67 index obtained by immunohistochemical staining. Results  On semiquantitative analysis, MET exhibited a slightly higher sensitivity (87.8%) in tumor detection than FLT (83.3%), and both tracers were 100% sensitive for malignant gliomas. Low-grade gliomas that were false negative on MET-PET also were false negative on FLT-PET. Although the difference of MET SUV_max and T/N ratio between grades II and IV gliomas was statistically significant (P < 0.001), there was a significant overlap of MET uptake in the tumors. The difference of MET SUV_max and T/N ratio between grades II and III gliomas was not statistically significant. Low-grade gliomas with oligodendroglial components had relatively high MET uptake. The difference of FLT SUV_max and T/N ratio between grades III and IV gliomas was statistically significant (P < 0.01). Again, the difference of FLT SUV_max and T/N ratio between grades II and III gliomas was not statistically significant. Grade III gliomas with non-contrast enhancement on MR images had very low FLT uptake. In 18 patients who underwent PET examination with both tracers, a significant but relatively weak correlation was observed between the individual SUV_max of MET and FLT (r = 0.54, P < 0.05) and T/N ratio of MET and FLT (r = 0.56, P < 0.05). Total FLT uptake in the tumor had a higher correlation (r = 0.89, P < 0.001) with Ki-67 proliferation index than MET uptake (r = 0.49, P < 0.01). Conclusions  PET studies using MET and FLT are useful for tumor detection in newly diagnosed gliomas. However, there is no complimentary information in tumor detection with simultaneous measurements of MET- and FLT-PET in low grade gliomas. FLT-PET seems to be superior than MET-PET in noninvasive tumor grading and assessment of proliferation activity in gliomas of different grades.     

Detection of gastric cancer using <Superscript>18</Superscript>F-FLT PET: comparison with <Superscript>18</Superscript>F-FDG PET

Purpose  We prospectively investigated the feasibility of 3′-deoxy-3′-¹⁸F-fluorothymidine (FLT) positron emission tomography (PET) for the detection of gastric cancer, in comparison with 2-deoxy-2-¹⁸F-fluoro-d-glucose (FDG) PET, and determined the degree of correlation between the two radiotracers and proliferative activity as indicated by Ki-67 index. Methods  A total of 21 patients with newly diagnosed advanced gastric cancer were examined with FLT PET and FDG PET. Tumour lesions were identified as areas of focally increased uptake, exceeding that of surrounding normal tissue. For semiquantitative analysis, the maximal standardized uptake value (SUV) was calculated. Results  For detection of advanced gastric cancer, the sensitivities of FLT PET and FDG PET were 95.2% and 95.0%, respectively. The mean (±SD) SUV for FLT (7.0 ± 3.3) was significantly lower than that for FDG (9.4 ± 6.3 p < 0.05). The mean FLT SUV and FDG SUV in nonintestinal tumours were higher than in intestinal tumours, although the difference was not statistically significant. The mean (±SD) FLT SUV in poorly differentiated tumours (8.5 ± 3.5) was significantly higher than that in well and moderately differentiated tumours (5.3 ± 2.1; p < 0.04). The mean FDG SUV in poorly differentiated tumours was higher than in well and moderately differentiated tumours, although the difference was not statistically significant. There was no significant correlation between Ki-67 index and either FLT SUV or FDG SUV. Conclusion  FLT PET showed as high a sensitivity as FDG PET for the detection of gastric cancer, although uptake of FLT in gastric cancer was significantly lower than that of FDG.     

PET/CT with Gluc-Lys-([<Superscript>18</Superscript>F]FP)-TOCA: correlation between uptake,size and arterial perfusion in somatostatin receptor positive lesions

Purpose Somatostatin receptor (sstr) positive tumours vary widely in uptake of radiolabelled somatostatin (sst) analogues. This study determinates variability in lesion uptake of the glycosylated sst analogon N^α-(1-deoxy-d-fructosyl)-N^ɛ-(2-[¹⁸F]fluoropropionyl)-Lys⁰-Tyr³-octreotate (Gluc-Lys([¹⁸F]FP)-TOCA) and correlates it with lesion size and arterial perfusion as measured on computed tomography (CT). Methods Ten patients with metastasized neuroendocrine carcinomas were investigated with positron emission tomography PET/CT (Biograph 16, Siemens, Germany). Lesion standardized uptake values (SUVs) were determined at ∼50 min post tracer injection according to a 60% isocontour volume of interest around each lesion. Lesion size and enhancement in the arterial phase (hounsfield units, HUs) were derived from CT. Results 114 lesions in the upper abdomen had a correlate on both, PET and CT. Variability in lesion SUVs was high (SUV_mean 22 ± 13). Intraindividually, there was a sigmoid positive correlation between lesion SUV and lesion diameter indicating partial volume effects. Residual variability in lesions ≥3 cm (≥2.5 cm) ranged down to about half (third) of the maximum lesion uptake and remained unexplained by partial volume effects. No correlation with measured HU in the arterial phase was found, neither intraindividually nor interindividually. Conclusion Partial volume effects were a major source of intraindividual variability in tumour tracer uptake. Lesions below 2.5 to 3 cm should thus be used with caution when performing dose calculations. In larger lesions residual variability in uptake must be considered; it may be due to variable sstr2 expression on the tumours’ cell surfaces.     

Double-phase <Superscript>18</Superscript>F-FDG PET-CT for determination of pulmonary tuberculoma activity

Purpose The aim of this study is to evaluate the potential role of double phase acquisition of ¹⁸F fluorodeoxyglucose (FDG) positron emission tomography (PET) for the differentiation of active pulmonary tuberculoma. Methods A total of 25 consecutive patients with pulmonary tuberculoma were enrolled. PET/CT imaging was performed 60 (range 53–71) and 120 min (range 109–131) after injection of ¹⁸F-FDG. The intensity of ¹⁸F-FDG uptake by pulmonary lesions was assessed visually, and the intensity was scored with a four-point scale (grade 1: absent, grade 2: faint, grade 3: moderate, grade 4: intense). Results Active tuberculoma shows statistically significant higher values in maximal standardized uptake values SUV_maxE (active = 2.3 ± 0.75, inactive = 0.79 ± 0.15), SUV_maxD (active = 2.48 ± 0.79, inactive = 0.75 ± 0.13), and %ΔSUV_max (active = 8.07 ± 7.77%, inactive = −3.83 ± 6.59) than those of inactive tuberculoma. When greater than or equal to visual grade 2 was used as the cutoff value, the sensitivity and specificity were 100 and 81.8%. When SUV_maxE 1.05 was used as the cutoff point, the sensitivity and specificity were 100 and 100%. When SUV_maxD 0.97 was used as the cutoff value, the sensitivity and specificity were 92.8 and 100%. When %ΔSUV_max 6.59 was used as the cutoff value, the sensitivity and specificity were 71.4 and 100%. The %ΔSUV_max was the potent predictor by logistic regression analysis. Conclusion The ΔSUV_max is a potential predictor for activity of pulmonary tuberculoma. However, the diagnostic performances were similar between visual and quantitative analyses. The visual assessment may be sufficient for determination of pulmonary tuberculoma activity. Further studies are needed to confirm these results and improve statistical accuracy. In-Ju Kim and Jung Sub Lee equally contributed to the current study.     

2-deoxy-2-[18F]fluoro-d-galactose: A new tracer for the measurement of galactose metabolism in the liver by position emission tomography

We prepared 2-deoxy-2-[¹⁸F]fluoro-d-galactose as a potential radiopharmaceutical for liver imaging and for the assessement by position emission tomography of regional metabolic function of the liver. In biodistribution studies of rats, the liver uptake of the compound was very high, almost reaching a plateau (6.33% dose/g) at 30 min and remaining constant until 120 min. This high uptake was reduced by simultaneous administration of d-galactose, but d-glucose had no effect. The compound was much less concentrated in the liver that had been damaged by CCl₄ treatment. Positron imaging of a rabbit liver showed a remarkable uptake of the compound with a high liver-to-blood ratio. The high concentration in the liver was also reduced by the administration of d-galactose. These data suggest that the compound was trapped in the liver by a metabolic process and could be used for the measurement by position emission tomography of galactose metabolism in the liver.     

Tumour enhancing fraction (EnF) in glioma: relationship to tumour grade

The aim of this research was to determine whether the proportion of a tumour that enhances (enhancing fraction, EnF) and changes in EnF with enhancement threshold differ between low and high grade glioma. Forty-four patients (45 gliomas comprising 16 grade II, 5 grade III and 24 grade IV) were studied. Imaging included pre- and post-contrast-enhanced T₁-weighted sequences and T₁-weighted DCE-MRI. Thresholded enhancement maps were generated for each tumour by using a range of values of the initial area under the contrast concentration curve (IAUC). A plot of EnF versus threshold value was generated. We examined the relationship between tumour grade and enhancement metrics including: EnF (threshold IAUC > 0 mMol s), EnF (threshold IAUC > 2.5 mMol s), initial slope of the EnF/threshold curve (∂EnF), IAUC, and two previously described signal-intensity-based metrics. EnF, defined as the proportion of tumour showing any enhancement (threshold IAUC > 0 mMol s), showed no difference between low and high grade glioma. All other measures demonstrated significant differences between grade II and IV, and low (grade II) and high grade (grades III/ IV) gliomas (p < 0.01). Two measures, ∂EnF and Pronin’s measure of enhancement, showed differences between grade III and IV (p < 0.05). No measure separated grade II from III. Metrics which describe the enhancing fraction and its variation with enhancement threshold ∂EnF show considerably different behaviour in low and high grade tumours. These observations suggest that these metrics may provide important biological information concerning tumour biology and therapeutic responses and encourage further research to characterise and validate these novel biomarkers.     

<Superscript>123</Superscript>I-Interleukin-2 uptake in squamous cell carcinoma of the head and neck carcinoma

Introduction Information obtained on the IL-2 receptor status of tumour infiltrating lymphocytes in patients suffering from squamous cell carcinoma of the head and neck (SSCHN) before and after IL-2 treatment may lead to a better understanding of the immunological changes and related kinetics induced at the tumour level and ultimately to a strategy that allows selection of those patients that will benefit from IL-2 therapy. This study set out to assess the relationship between ¹²³I-IL2 single-photon emission computed tomography (SPECT) findings and the presence of IL-2 receptors (CD25 staining) on tumour-infiltrating lymphocytes as well as on SCCHN tumour cells in patients suffering from SCCHN. Materials and methods Seventeen consecutive patients (12 men; mean age, 57 years) highly suspected to suffer from SSCHN were prospectively included in the study. All patients underwent planar and whole body ¹²³I-IL2 scintigraphy and underwent surgery or had a biopsy taken within 1 week from imaging. Surgical resected primary lesions as well as biopsy material from primary tumours were histologically analysed with respect to the presence and intensity of CD25 expression on tumour infiltrating lymphocytes and tumour cells (HSCORE). Tumor-to-background (T/N) ratios of the primary tumour derived from planar and tomographic ¹²³I-IL2 scintigraphy were related to the results derived from histology. Results All patients suffered from SSCHN. T/N ratios derived from SPECT images were significantly correlated with CD25 lymphocyte HSCOREs (r = 0.66; p = 0.03), but not with CD25 tumour cell HSCOREs. Conclusions ¹²³I-IL-2 SPECT imaging allows for non-invasive imaging of the relative amount of IL-2 receptors present on tumour infiltrating lymphocytes in SCCHN.     

Functional imaging of multidrug resistance in an orthotopic model of osteosarcoma using 99mTc-sestamibi

Purpose The purpose of this work was the development of an orthotopic model of osteosarcoma based on luciferase-expressing tumour cells for the in vivo imaging of multidrug resistance (MDR) with ^99mTc-sestamibi. Methods Doxorubicin-sensitive (143B-luc⁺) and resistant (MNNG/HOS-luc⁺) osteosarcoma cell lines expressing different levels of P-glycoprotein and carrying a luciferase reporter gene were inoculated into the tibia of nude mice. Local tumour growth was monitored weekly by bioluminescence imaging and X-ray. After tumour growth, a ^99mTc-sestamibi dynamic study was performed. A subset of animals was pre-treated with an MDR inhibitor (PSC833). Images were analysed for calculation of ^99mTc-sestamibi washout half-life (t _1/2), percentage washout rate (%WR) and tumour/non-tumour (T/NT) ratio. Results A progressively increasing bioluminescent signal was detected in the proximal tibia after 2 weeks. The t _1/2 of ^99mTc-sestamibi was significantly shorter (p < 0.05) in drug-resistant MNNG/HOS-luc⁺ tumours (t _1/2 = 87.3 ± 15.7 min) than in drug-sensitive 143B-luc⁺ tumours (t _1/2 = 161.0 ± 47.4 min) and decreased significantly with PSC833 (t _1/2 = 173.0 ± 24.5 min, p < 0.05). No significant effects of PSC833 were observed in 143B-luc⁺ tumours. The T/NT ratio was significantly lower (p < 0.05) in MNNG/HOS-luc⁺ tumours than in 143B-luc⁺ tumours at early (1.55 ± 0.22 vs 2.14 ± 0.36) and delayed times (1.12 ± 0.11 vs 1.62 ± 0.33). PSC833 had no significant effects on the T/NT ratios of either tumour. Conclusion The orthotopic injection of tumour cells provides an animal model suitable for functional imaging of MDR. In vivo bioluminescence imaging allows the non-invasive monitoring of tumour growth. The kinetic analysis of ^99mTc-sestamibi washout provides information on the functional activity of MDR related to P-glycoprotein expression and its pharmacological inhibition in osteosarcoma.     

Target volume definition for <Superscript>18</Superscript>F-FDG PET-positive lymph nodes in radiotherapy of patients with non-small cell lung cancer

Purpose FDG PET is increasingly used in radiotherapy planning. Recently, we demonstrated substantial differences in target volumes when applying different methods of FDG-based contouring in primary lung tumours (Nestle et al., J Nucl Med 2005;46:1342–8). This paper focusses on FDG-positive mediastinal lymph nodes (LN_PET). Methods In our institution, 51 NSCLC patients who were candidates for radiotherapy prospectively underwent staging FDG PET followed by a thoracic PET scan in the treatment position and a planning CT. Eleven of them had 32 distinguishable non-confluent mediastinal or hilar nodal FDG accumulations (LN_PET). For these, sets of gross tumour volumes (GTVs) were generated at both acquisition times by four different PET-based contouring methods (visual: GTV_vis; 40% SUV_max: GTV₄₀; SUV=2.5: GTV_2.5; target/background (T/B) algorithm: GTV_bg). Results All differences concerning GTV sizes were within the range of the resolution of the PET system. The detectability and technical delineability of the GTVs were significantly better in the late scans (e.g. p = 0.02 for diagnostic application of SUV_max = 2.5; p = 0.0001 for technical delineability by GTV_2.5; p = 0.003 by GTV₄₀), favouring the GTV_bg method owing to satisfactory overall applicability and independence of GTVs from acquisition time. Compared with CT, the majority of PET-based GTVs were larger, probably owing to resolution effects, with a possible influence of lesion movements. Conclusion For nodal GTVs, different methods of contouring did not lead to clinically relevant differences in volumes. However, there were significant differences in technical delineability, especially after early acquisition. Overall, our data favour a late acquisition of FDG PET scans for radiotherapy planning, and the use of a T/B algorithm for GTV contouring.     

<Superscript>124</Superscript>I-L19-SIP for immuno-PET imaging of tumour vasculature and guidance of <Superscript>131</Superscript>I-L19-SIP radioimmunotherapy

Purpose  The human monoclonal antibody (MAb) fragment L19-SIP is directed against extra domain B (ED-B) of fibronectin, a marker of tumour angiogenesis. A clinical radioimmunotherapy (RIT) trial with ¹³¹I-L19-SIP was recently started. In the present study, after GMP production of ¹²⁴I and efficient production of ¹²⁴I-L19-SIP, we aimed to demonstrate the suitability of ¹²⁴I-L19-SIP immuno-PET for imaging of angiogenesis at early-stage tumour development and as a scouting procedure prior to clinical ¹³¹I-L19-SIP RIT. Methods   ¹²⁴I was produced in a GMP compliant way via ¹²⁴Te(p,n)¹²⁴I reaction and using a TERIMO™ module for radioiodine separation. L19-SIP was radioiodinated by using a modified version of the IODO-GEN method. The biodistribution of coinjected ¹²⁴I- and ¹³¹I-L19-SIP was compared in FaDu xenograft-bearing nude mice, while ¹²⁴I PET images were obtained from mice with tumours of <50 to ∼700 mm³. Results   ¹²⁴I was produced highly pure with an average yield of 15.4 ± 0.5 MBq/μAh, while separation yield was ∼90% efficient with <0.5% loss of TeO₂. Overall labelling efficiency, radiochemical purity and immunoreactive fraction were for ¹²⁴I-L19-SIP: ∼80 , 99.9 and >90%, respectively. Tumour uptake was 7.3 ± 2.1, 10.8 ± 1.5, 7.8 ± 1.4, 5.3 ± 0.6 and 3.1 ± 0.4%ID/g at 3, 6, 24, 48 and 72 h p.i., resulting in increased tumour to blood ratios ranging from 6.0 at 24 h to 45.9 at 72 h p.i.. Fully concordant labelling and biodistribution results were obtained with ¹²⁴I- and ¹³¹I-L19-SIP. Immuno-PET with ¹²⁴I-L19-SIP using a high-resolution research tomograph PET scanner revealed clear delineation of the tumours as small as 50 mm³ and no adverse uptake in other organs. Conclusions   ¹²⁴I-MAb conjugates for clinical immuno-PET can be efficiently produced. Immuno-PET with ¹²⁴I-L19-SIP appeared qualified for sensitive imaging of tumour neovasculature and for predicting ¹³¹I-L19-SIP biodistribution. Bernard M. Tijink and Lars R. Perk contributed equally to this article.     

Value of <Emphasis Type="Italic">O</Emphasis>-(2-[<Superscript>18</Superscript>F]fluoroethyl)-<Emphasis Type="SmallCaps">l</Emphasis>-tyrosine PET for the diagnosis of recurrent glioma

Purpose The prognosis of patients with recurrent gliomas depends on reliable and early diagnosis of tumour recurrence after initial therapy. In this context, magnetic resonance imaging (MRI) and computed tomography (CT) often fail to differentiate between radiation- and tumour-induced contrast enhancement. Furthermore, absence of contrast enhancement, or even of ¹⁸F-fluorodeoxyglucose uptake in PET, does not exclude recurrence. The aim of this study was to establish the diagnostic value of O-(2-[¹⁸F]fluoroethyl)-l-tyrosine (FET) PET in recurrent gliomas.Methods Fifty-three patients with glioma (primary grading: 27=WHO grade IV, 16=grade III, 9=grade II, 1=grade I) and clinically suspected recurrence underwent FET PET scans 4–180 months after different treatment modalities. For semiquantitative evaluation, maximal SUV (SUV_max) and mean SUV within 80% and 70% isocontour thresholds (SUV₈₀/SUV₇₀) were evaluated and the respective ratios to the background (BG) were calculated. PET results were correlated with MRI/CT, clinical follow-up or biopsy findings.Results All patients presented with FET uptake, of varying intensity, in the area of the primary tumour after initial therapy. In the 42 patients with confirmed recurrence, there was additional distinct focal FET uptake with significantly higher values compared with those in the 11 patients without clinical signs of recurrence and showing only low and homogeneous FET uptake at the margins of the resection cavity. With respect to tumour grading, there was a slight but non-significant increase from WHO II (SUV_max/BG: 2.53±0.28) to WHO III (SUV_max/BG: 2.84±0.49) and WHO IV (SUV_max/BG: 3.55±1.07) recurrence.Conclusion FET PET reliably distinguishes between post-therapeutic benign lesions and tumour recurrence after initial treatment of low- and high-grade gliomas.     

Risk stratification and prediction of cancer of focal thyroid fluorodeoxyglucose uptake during cancer evaluation

Background  

Focal thyroid incidentaloma by F-18 2-deoxy-2-F18-fluoro-d-glucose (FDG) positron emission tomography (PET) has been reported 1–4% of cancer patients and normal healthy population, with a risk of cancer ranging 14–50%. The aim of this study was to investigate the prevalence of thyroid incidentaloma in F-18 FDG PET/CT and risk of cancer, usefulness of visual and SUV_max and SUV_mean differentiating malignant nodules and to define the predictable variables.     

Radioembolisation with <Superscript>90</Superscript>Y-microspheres: dosimetric and radiobiological investigation for multi-cycle treatment

Introduction  Radioembolisation with ⁹⁰Y-microspheres is a new locoregional treatment of hepatic lesions, usually applied as single cycle. Multi-cycle treatments might be considered as a strategy to improve the risk-benefit balance. With the aim to derive suitable information for patient tailored therapy, available patients’ dosimetric data were reviewed according to the linear–quadratic model and converted into biological effective dose (BED) values. Single vs. multi-cycle approaches were compared through radiobiological perspective. Materials and methods  Twenty patients with metastatic lesions underwent radioembolisation. The ⁹⁰Y-administered activity (AA) was established in order to respect a precautionary limit dose (40 Gy) for the non-tumoral liver (NTL). BED was calculated setting α/β = 2.5 Gy (NTL), 10 Gy (tumours); T _1/2,eff = T _1/2,phys = 64.2 h; T _1/2,rep = 2.5 h (NTL), 1.5 h (tumours). The BED to NTL was considered as a constraint for multi-cycle approach. The AA for two cycles and the percent variations of AA, tumour dose, BED were estimated. Results  In one-cycle, for a prescribed BED to NTL of 64 Gy (NTL dose = 40 Gy), AA was 1.7 (0.9–3.2) GBq, tumour dose was 130 (65–235) Gy, and tumour BED was 170 (75–360) Gy. Considering two cycles, ∼15% increase was found for AA and dose to NTL, with unvaried BED for NTL. Tumour dose increase was 20 (10–35) Gy; tumour BED increase was 10 (3–11) Gy. In different protocols allowing 80 Gy to NTL, the BED sparing estimated was ∼50 Gy (two cycles) and 65 Gy (three cycles). Conclusions  From a radiobiological perspective, multi-cycle treatments would allow administering higher activities with increased tumour irradiation and preserved radiation effects on NTL. Trials comparing single vs. multiple cycles are suggested.     

The somatostatin receptor-targeted radiotherapeutic [90Y-DOTA-dPhe1,Tyr3]octreotide (90Y-SMT 487) eradicates experimental rat pancreatic CA 20948 tumours

Somatostatin receptor-expressing tumours are potential targets for therapy with radiolabelled somatostatin analogues. We have synthesized a number of such analogues in the past and identified [DOTA-dPhe¹, Tyr³]octreotide (SMT 487) as the most promising candidate molecule because of its advantageous properties in cellular and in vivo tumour models. In the current paper we describe the radiotherapeutic effect of yttrium-90 labelled SMT 487 in Lewis rats bearing the somatostatin receptor-positive rat pancreatic tumour CA 20948. SMT 487 binds with nanomolar affinity to both the human and the rat somatostatin receptor subtype 2 (sst₂) (human sst₂ IC₅₀=0.9 nM, rat sst₂ IC₅₀=0.5 nM). In vivo, ⁹⁰Y-SMT 487 distributed rapidly to the sst₂ expressing CA 20948 rat pancreatic tumour, with a tumour-to-blood ratio of 49.15 at 24 h post injection. A single intravenous administration of 10 mCi/kg ⁹⁰Y-SMT 487 resulted in a complete remission of the tumours in five out of seven CA 20948 tumour-bearing Lewis rats. No regrowth of the tumours occurred 8 months post injection. Control animals that were treated with 30 μg/kg of unlabelled SMT 487 had to be sacrificed 10 days post injection due to excessive growth or necrotic areas on the tumour surface. Upon re-inoculation of tumour cells into those rats that had shown complete remission, the tumours disappeared after 3–4 weeks of moderate growth without any further treatment. The present study shows for the first time the curative potential of ⁹⁰Y-SMT 487-based radiotherapy for somatostatin receptor-expressing tumours. Clinical phase I studies with yttrium-labelled SMT 487 have started in September 1997. Received 14 January and in revised form 16 March 1998     

In vivo imaging of integrin ανβ<Subscript>3</Subscript> expression using fluorescence-mediated tomography

Purpose Optical imaging would be desirable for cancer diagnostics since it can potentially resolve relevant oncological target structures in vivo. We therefore synthesised an αvβ₃ targeted fluorochrome and imaged tumour xenografts with different αvβ₃ expression levels using both planar and tomographic optical imaging methods. Methods An αvβ₃-targeted RGD peptide was labelled with a cyanine dye (Cy 5.5). Binding of the optical tracer was tested on M21 melanoma (n = 5), HT-1080 fibrosarcoma (n = 6) and MCF-7 adenocarcinoma (n = 5) cells and their tumour xenografts. All optical imaging studies were performed using two-dimensional planar fluorescence reflectance imaging (FRI) technology and three-dimensional fluorescence-mediated tomography (FMT). Results In vitro, the peptide-dye conjugate showed a clear binding affinity to αvβ₃-positive M21 and HT-1080 cells while αvβ₃-negative MCF-7 cells and pre-dosing with the free RGD peptide revealed little to no fluorescence. In vivo, tumour xenografts were clearly visualised by FRI and FMT up to 24 h post injection. FMT allowed quantification of the fluorochrome distribution in deeper tissue sections showing an average fluorochrome concentration of 417.61 ± 105.82 nM Cy 5.5 (M21), 353.68 ± 54.02 nM Cy 5.5 (HT-1080) and 262.83 ± 155.36 nM Cy 5.5 (MCF-7) in the target tissue 60 min after tracer administration. Competition with the free RGD peptide resulted in a reduction in the fluorochrome concentration in M21 tumour tissue (294.35 ± 84.27 nM). Conclusion RGD-Cy 5.5 combined with novel tomographic optical imaging methods allows non-invasive imaging of tumour-associated αvβ₃ expression and may thus be a promising strategy for sensitive evaluation of tumour target expression.