Significant dose reduction is feasible in FDG PET/CT protocols without compromising diagnostic quality.

PURPOSE: To reduce the radiation dose to patients by optimizing oncological FDG PET/CT protocols. METHODS: The baseline PET/CT protocol in our institution for oncological PET/CT examinations consisted of the administration of 5.18 MBq/kg of FDG and a CT acquisition with a reference current-time product of 120 mAs. In 2016, FDG activity was reduced to 4.44 and 3.70 MBq/kg and reference CT current-time-product was reduced to 100 and 80 mAs. 322 patients scanned with different protocols were retrospectively evaluated. For each patient, effective dose was calculated. The overall image quality was subjectively rated by the referring physician on a 4-point scale (IQ score: 1 excellent, 2 good, 3 poor but interpretable, 4 poor not interpretable). Image quality was quantitatively evaluated measuring noise in the liver. RESULTS: CT Results: Effective dose was progressively reduced from 9.5 ±â€¯2.8 to 8.0 ±â€¯2.3 and 6.2 ±â€¯1.5 mSv (p < 0.001). A mean dose reduction of 34.9% was achieved. There was a significant degradation of IQ score (p < 0.05) and noise (p < 0.001). Nevertheless, the number of poor quality studies (IQ score >2) did not increase. PET Results: Effective dose was gradually reduced from 6.5 ±â€¯1.4 to 5.7 ±â€¯1.3 and 5.0 ±â€¯1.0 mSv (p < 0.001). Average dose reduction was 23.4%. IQ score (p < 0.05) and noise (p < 0.001) significantly degraded for lower activity protocols. However, all images with reduced activity were scored as interpretable (IQ score ≤ 3). CONCLUSIONS: A significant radiation dose reduction of 28.7% was reached. Despite a slight reduction in image quality, the new regime was successfully implemented with readers reporting unchanged clinical confidence.

Impact of time-of-flight and point-spread-function in SUV quantification for oncological PET.

BACKGROUND: Accuracy in the quantification of the SUV is a critical point in PET because proper quantification of tumor uptake is essential for therapy monitoring and prognosis evaluation. Recent advances such as time-of-flight (TOF) and point-spread-function (PSF) reconstructions have dramatically improved detectability. However, first experiences with these techniques have shown a consistent tendency to measure markedly high SUV values, bewildering nuclear medicine physicians and referring clinicians. PURPOSE: We investigated different reconstruction and quantification procedures to determine the optimum protocol for an accurate SUV quantification in last generation PET scanners. METHODS: Both phantom and patient images were evaluated. A complete set of experiments was performed using a body phantom containing 6 spheres with different background levels and contrasts. Whole-body FDG PET/CT of 20 patients with breast and lung cancer was evaluated. One hundred five foci were identified by 2 experienced nuclear medicine physicians.Each acquisition was reconstructed both with classical and advanced (TOF, PSF) reconstruction techniques. Each sphere and each in vivo lesion was quantified with different parameters as follows: SUV(max), SUV(mean), and SUV(50) (mean within a 50% isocontour). RESULTS: This study has confirmed that quantification with SUV(max) produces important overestimation of metabolism in new generation PET scanners. This is a relevant result because, currently, SUV(max) is the standard parameter for quantification. SUV(50) has been shown as the best alternative, especially when applied to images reconstructed with PSF + TOF. CONCLUSIONS: SUV(50) provides accurate quantification and should replace SUV(max) in PET tomographs incorporating advanced reconstruction techniques. PSF + TOF reconstruction is the optimum for both detection and accurate quantification.

Molecular imaging techniques to study the biodistribution of orally administered (99m)Tc-labelled naive and ligand-tagged nanoparticles.

PURPOSE: Study by molecular imaging the biodistribution of poly(anhydride) nanoparticles after oral administration. PROCEDURES: Poly (anhydride) nanoparticles (NP) and cyclodextrin-tagged nanoparticles (CD-NP) were radiolabelled with (99m)Tc. Radiochemical purity was measured with a double-solvent chromatography system and the absence of undesirable components was confirmed by size and polydispersion measurement of the technetium-labelled nanoparticles by photon correlation spectroscopy. Single photon emission computed tomography (SPECT) fused computed tomography (CT) in vivo molecular imaging was used for biodistribution studies in small animals. RESULTS: SPECT-CT images revealed activity only in the gastrointestinal tract. Thirteen percent of the given dose of CD-NP and 3% of the given dose of conventional NP were found in the stomach at 8 h. CONCLUSION: No evidence of translocation or distribution out of gastrointestinal tract was found. CD-NP moved significantly more slowly inside the gut than conventional NP, probably due to their physico-chemical structure that allows stronger interactions with the gut mucosa.

[Usefulness of PET scans in diagnosing recurrent prostate cancer. Prostate with PSA level < 5 ng/ml]. / Valor de la PET en la recurrencia del cáncer de próstata con PSA < 5 ng/ml.

INTRODUCTION AND OBJECTIVES: We intend to evaluate the usefulness of PET scans in diagnosing recurrent prostate cancer after a curative attempt using radical treatment. MATERIAL AND METHODS: 92 consecutive prostate cancer patients in biochemical progression following radical surgery (63) or radiation treatment (29) were studied with positron emission tomography (PET). In all cases two scans were performed in the same day (11C-choline and 18F-FDG). PET efficacy was evaluated both globally (by employing the results achieved with both 11C-choline and 18F-FDG) and using both radiotracers independently to detect recurrence in patients with biochemical progression. For this purpose, we used comparison of means for k-independent samples, 2 x 2 and 2 x X contingency tables and ROC curves. RESULTS: 1. Global PET: there is evidence of PET alteration regarding the PSA level (P=.003): the clinical stage (P=.01). There are no statistically significant PET alterations regarding the affected biopsy (uni or bilateral), surgical margins, pathological stage and time to progression. ROC curve PET-PSA is statistically significant (P< .0001) permitting calculation of different cut-off points, with a specificity of 91% (highest) for a PSA of 4.3 ng/ml. 2. PET 18FDG: the area under the ROC curve is statistically significant (P< .0001) with a specificity of 91% for a PSA of 6.51 ng/ml. 3. PET 11choline: the area under the ROC curve is statistically significant (P< .0001) with a specificity of 91% for a PSA of 5.15 ng/ml. CONCLUSIONS: PET is a useful tool for diagnosing prostate cancer recurrence after a curative attempt using radical treatment.

Valor de la PET en la recurrencia del cáncer de próstata con PSA < 5 ng/ml / Usefulness of PET scans in diagnosing recurrent prostate cancer. Prostate with PSA level < 5 ng/ml

Introducción y objetivo: Evaluamos la utilidad de la tomografía por emisión de positrones (PET) en el diagnóstico de la recurrencia del cáncer de próstata tras tratamiento con intención curativa. Material y métodos: Se sometió a 92 pacientes consecutivos en progresión bioquímica tras cirugía radical (63) o radioterapia (29) a una PET. En todos los casos, se realizaron dos escáneres PET en el mismo día (11C-colina y 18F-FDG). Se evalúa la eficacia de la PET de manera global (utilizando los resultados con 11C-colina y 18F-FDG) y de manera independiente para detectar recurrencia en pacientes con progresión bioquímica. Para ello, se utilizan la comparación de medias para k muestras independientes, tablas de contingencia 2 × 2 y 2× X y curvas ROC. Resultados: 1. PET global: hay evidencia de la alteración de la PET en función del antígeno prostático específico (PSA) (p = 0,003), estadio clínico (p = 0,01). No existe una alteración de la PET estadísticamente significativa en función de la afectación de la biopsia (unilateral o bilateral), los márgenes quirúrgicos, el estadio patológico y el tiempo a progresión. La curva ROC PET-PSA es significativa (p < 0,0001) y permite calcular distintos puntos de corte; PSA = 4,3 ng/ml el que presenta una mayor especificidad (91%). 2. PET 18FDG: el área bajo la curva ROC es significativa (p < 0,0001), con una especificidad del 91% para un PSA =6,51 ng/ml. 3. PET 11colina: el área bajo la curva ROC es significativa (p < 0,0001), con una especificidad del 91% para un PSA = 5,15 ng/ml. Conclusiones: La PET es una herramienta útil en el diagnóstico de la recurrencia de cáncer de próstata tras tratamiento radical con intención curativa (AU)

Introduction and objectives: We intend to evaluate the usefulness of PET scans in diagnosing recurrent prostate cancer after a curative attempt using radical treatment. Material and methods: 92 consecutive prostate cancer patients in biochemical progression following radical surgery (63) or radiation treatment (29) were studied with positron emission tomography (PET). In all cases two scans were performed in the same day (11C-cholineand 18F-FDG). PET efficacy was evaluated both globally (by employing the results achieved with both 11C-choline and 18F-FDG) and using both radiotracers independently to detect recurrence in patients with biochemical progression. For this purpose, we used comparison of means for k-independent samples, 2 × 2 and 2 × X contingency tables and ROC curves. Results: 1. Global PET: there is evidence of PET alteration regarding the PSA level (P=0.003): the clinical stage (P=0.01). There are no statistically significant PET alterations regarding the affected biopsy (uni or bilateral), surgical margins, pathological stage and time to progression. ROC curve PET-PSA is statistically significant (P<0.0001) permitting calculation of different cut-off points, with a specificity of 91% (highest) for a PSA of 4.3 ng/ml. 2. PET18FDG: the area under the ROC curve is statistically significant (P<0.0001) with a specificity of91% for a PSA of 6.51 ng/ml. 3. PET 11choline: the area under the ROC curve is statistically significant (P<0.0001) with a specificity of 91% for a PSA of 5.15 ng/ml. Conclusions: PET is a useful tool for diagnosing prostate cancer recurrence after a curative attempt using radical treatment (AU)

Diagnostic accuracy of FDG PET in the follow-up of platinum-sensitive epithelial ovarian carcinoma.

PURPOSE: This study was designed to retrospectively evaluate the diagnostic yield of FDG PET for the diagnosis of recurrent ovarian cancer. METHODS: Eighty FDG PET scans were performed on 55 patients owing to suspicion of relapse, and 45 FDG PET scans were performed on 31 patients who were clinically disease free. PET results were compared with the results of conventional radiological imaging (CIM) and serum CA 125 levels, and related to pathological findings in 54 cases or clinical follow-up in 71 cases. RESULTS: CIM correctly identified 49 cases with recurrence [sensitivity (SE) 53.3%] ,and there were 27 true negatives [specificity (SP) 81.8%] However, 43 cases were false negative and six were false positive. The positive predictive value (PPV), negative predictive value (NPV) and accuracy (ACC) of CIM were 89%, 38.6% and 60.8%, respectively. FDG PET correctly detected recurrent disease in 80/92 cases (SE 86.9%, p<0.05) and ruled out relapse in 26/33 cases (SP=78.8%). The PPV, NPV and ACC of PET were 91.9%, 68.4% and 84.8%, respectively. Standardised uptake values did not provide additional diagnostic accuracy compared with visual analysis. The CA 125 results showed an SE of 57.6%, an SP of 93.9% and an ACC of 67.2%. In 23 patients with positive serum CA 125 levels, but negative CIM, FDG PET was positive and relapse was confirmed. Furthermore, FDG PET was positive and relapse was confirmed in 11 patients with negative serum CA 125 levels and CIM. CONCLUSION: FDG PET may detect recurrent ovarian cancer earlier than CIM, with higher sensitivity and even higher diagnostic accuracy.

Simple automated system for simultaneous production of 11C-labeled tracers by solid supported methylation.

We herein describe a simple setup for the automated simultaneous synthesis of L-[methyl-11C]methionine and N-[methyl-11C]choline by solid-supported methylation. The setup is extremely simple and easy to adapt to other automated systems and due to its versatility, the method can be utilized for the production of other radiopharmaceuticals requiring a simple [11C]methylation step. Furthermore, it can be used for multiple simultaneous synthesis.