[en] To optimize the efficacy of radioimmunotherapy (RIT), the ideal antibody-radioisotope combinations should be used to deliver the highest tumor and the lowest normal tissue doses. In a mouse model, tumor and critical organ-absorbed doses delivered by different radioimmunoconjugates were calculated and compared. We used a Medical Internal Radiation Dosimetry (MIRD)-style mouse dosimetry model that incorporates cross-organ beta doses to make refined estimates of the radiation absorbed dose to tissues. Biodistribution data from neuroblastoma xenografted nude mice were used to estimate tumor, organ and bone marrow absorbed dose values for ⁹⁰Y-3F8, ¹³¹I-3F8 and ¹³¹I-F(ab')₂ fragments. Immunoreactive fractions of the radiolabeled antibodies were comparable. Although tumor uptake of the radioiodinated and radiometal labeled 3F8 was much higher than that of the radioiodinated F(ab')₂ fragments (maximum percent injected dose per gram values were 39.4, 33.2 and 20.1 for ¹³¹I-3F8, ⁹⁰Y-3F8 and ¹³¹I-F(ab')₂, respectively), tumor to nontumor ratios were higher for radioiodinated fragments (with the exception of tumor to kidney ratio). For the minimum tumor dose necessary for complete ablation, the bone marrow received 195, 278 and 401 cGy for ¹³¹I-F(ab')₂, ¹³¹I-3F8 and ⁹⁰Y-3F8, respectively. Tumor doses were 50.1, 232 and 992 cGy/MBq for ¹³¹I-F(ab')₂, ¹³¹I-3F8 and ⁹⁰Y-3F8, respectively. Tumor to bone marrow dose, which is defined as the therapeutic index, was 21.5, 14.7 and 10.4 for ¹³¹I-F(ab')₂, ¹³¹I-3F8 and ⁹⁰Y-3F8. ¹³¹I-F(ab')₂ fragments produced the highest therapeutic index but also the lowest tumor dose for radioimmunotherapy. Radiometal conjugated IgG produced the highest tumor dose but also the lowest therapeutic index

[en] The differentiation of the nature of a fluid collection as a complication of kidney transplantation is important for management and treatment planning. Early and delayed radionuclide renography can play an important role in the evaluation of a urine leak. However, it is sometimes limited in the evaluation of the exact location and extent of a urine leak. A 71-year-old male who had sudden anuria, scrotal swelling and elevated creatinine level after cadaveric renal transplantation performed Tc-99 m MAG3 renography to evaluate the renal function, followed by an ultrasound which was unremarkable. An extensive urine leak was evident on the planar images. However, an exact location of the urine leak was unknown. Accompanying SPECT/CT images confirmed a urine leak extending from the lower aspect of the transplant kidney to the floor of the pelvic cavity, presacral region and the scrotum via right inguinal canal as well as to the right abdominal wall. Renal scintigraphy is very useful to detect a urine leak after renal transplantation. However, planar imaging is sometimes limited in evaluating the anatomical location and extent of a urine leak accurately. In that case accompanying SPECT/CT images are very helpful and valuable to evaluate the anatomical relationships exactly

[en] Preclinical evaluation of the therapeutic potential of radiolabeled antibodies is commonly performed in a xenografted nude mouse model. To assess therapeutic efficacy it is important to estimate the absorbed dose to the tumor and normal tissues of the nude mouse. The current study was designed to accurately measure radiation does to human neuroblastoma xenografts and normal organs in nude mice treated with I-131-labeled 3F8 monoclonal antibody (MoAb) against disialoganglioside GD₂ antigen. Absorbed dose estimates were obtained using two different approaches: (1) measurement with teflon-imbedded CaSO₄:Dy mini-thermoluminescent dosimeters (TLDs) and (2) calculation using mouse S-factors. The calculated total dose to tumor one week after i.v. injection of the 50 μCi I-131-3F8 MoAb was 604 cGy. The corresponding decay corrected and not corrected TLD measurements were 109 ± 9 and 48.7 ± 3.4 cGy respectively. The calculated to TLD-derived dose ratios for tumor ranged from 6.1 at 24 h to 5.5 at 1 week. The light output fading rate was found to depend upon the tissue type within which the TLDs were implanted. The decay rate in humor, muscle, subcutaneous tissue and in vitro, were 9.5, 5.0, 3.7 and 0.67% per day, respectively. We have demonstrated that the type of tissue in which the TLD was implanted strongly influenced the in vivo decay of light output. Even with decay correction, a significant discrepancy was observed between MIRD-based calculated and CaSO₄:Dy mini-TLD measured absorbed doses. Batch dependence, pH of the tumor or other variables associated with TLDs which are not as yet well known may account for this discrepancy

[en] Amyloid positron emission tomography (PET) imaging with florbetapir ¹⁸F (¹⁸F-AV-45) allows in vivo assessment of cerebral amyloid load and can be used in the evaluation of progression of Alzheimer's disease (AD) and other dementias associated with b-amyloid. However, cortical amyloid deposition can occur in healthy cases, as well as in patients with AD and quantification of cortical amyloid burden can improve the ¹⁸F-AV-45 PET imaging evaluations. The quantification is mostly performed by cortical-to-cerebellum standardized uptake value ratio (SUVr). The aim of our study was to compare two methods for SUVr calculations in amyloid florbetapir ¹⁸F PET brain imaging. In amyloid florbetapir ¹⁸F PET brain imaging study, we imaged 42 cases with the mean age of 72.6 ± 9.9 (mean ± standard deviation). They were imaged on different PET/computed tomography systems with 369.0 ± 34.2 kBq of ¹⁸F florbetapir. Data were reconstructed using the vendor's reconstruction software. Corresponding magnetic resonance imaging (MRI) data were retrieved, and matched PET and MRI data were transferred to a common platform. Two methods were used for the calculation of the ratio of cortical-to-cerebellar signal (SUVr). One method was based on the MIM Software Inc., Version 6.4 software and only uses PET data. The second approach used the PMOD Neuro tool (version 3.5). This approach utilizes PET and corresponding MRI data (preferably T1-weighted) for better brain segmentation. For all the 42 cases, the average SUVr values for MIM and PMOD applications were 1.24 ± 0.26 and 1.22 ± 0.25, respectively, with a mean difference of 0.02 ± 0.15. The repeatability coefficient was 0.15 (12.3% of the mean). The Spearman's rank correlation coefficient was very high, r = 0.96. For amyloid-negative cases, the average SUVr values were lower than all group SUVr average values, 0.96 ± 0.07 and 1.00 ± 0.09, for MIM and PMOD applications, respectively. A mean difference was 0.04 ± 0.12, the repeatability coefficient was 0.12 (12.9% of the mean) and the Spearman's rank correlation coefficient was modest, r = 0.55. For amyloid-positive patients, the average SUVr values were higher than the same all grouP values, 1.34 ± 0.16 and 1.35 ± 0.20, respectively, with a mean difference of 0.01 ± 0.16. The repeatability coefficient was 0.16 (11.9% of the mean). The Spearman's rank correlation coefficient was high, r = 0.93. Our results indicated that the SUVr values derived using MIM and PMOD Neuro are effectively interchangeable and well correlated. However, PET template-based quantification (MIM approach) is clinically friendlier and easier to use. MRI template-based quantification (PMOD Neuro) better delineates different regions of the brain, can be used with any tracer, and therefore is more suitable for research. (author)

[en] The management approach in Hodgkin's (HL) and high-grade non-Hodgkin's lymphomas (NHL) has shifted towards reducing the toxicity and long-term adverse effects associated with treatment while maintaining favorable outcomes in low-risk patients. The success of an individualized treatment strategy depends largely on accurate diagnostic tests both at staging and during therapy. In this regard, positron emission tomography (PET) using fluorodeoxyglucose (FDG) with computed tomography (CT) has proved effective as a metabolic imaging tool with compelling evidence supporting its superiority over conventional modalities, particularly in staging and early evaluation of response. Eventually, this modality was integrated into the routine staging and restaging algorithm of lymphomas. This review will summarize the data on the proven and potential utility of PET/CT imaging for staging, response assessment, and restaging, describing current limitations of this imaging modality. (orig.)

[en] Highlights: PET/MRI post-therapy ⁹⁰Y studies are feasible and useful for ⁹⁰Y dosimetry calculations. Due to better MRI soft tissue contrast, liver contours are usually better seen in PET/MRI images than in MAA SPECT/CT images. The two main contributors to the difference between ⁹⁰Y dosimetry calculations using MAA versus ⁹⁰Y PET/MRI can be attributed to the changes in catheter positioning as well as the liver ROIs used for the calculations. ⁹⁰Y dosimetry values obtained from pre-therapy MAA SPECT/CT scans and PET/MRI post-therapy ⁹⁰Y studies were not significantly different. - Abstract: ObjectiveThe aim of our study was to compare yttrium -90 (⁹⁰Y) dosimetry obtained from pre-therapy ^99mTc-macroaggregated albumin (MAA) SPECT/CT versus post-therapy PET/MRI imaging among patients with primary or metastatic hepatic tumors.

[en] Segmentation of lymphoma lesions in FDG PET/CT images is critical in both assessing individual lesions and quantifying patient disease burden. Simple thresholding methods remain common despite the large heterogeneity in lymphoma lesion location, size, and contrast. Here, we assess 11 automated PET segmentation methods for their use in two scenarios: individual lesion segmentation and patient-level disease quantification in lymphoma. Lesions on ¹⁸F-FDG PET/CT scans of 90 lymphoma patients were contoured by a nuclear medicine physician. Thresholding, active contours, clustering, adaptive region-growing, and convolutional neural network (CNN) methods were implemented on all physician-identified lesions. Lesion-level segmentation was evaluated using multiple segmentation performance metrics (Dice, Hausdorff Distance). Patient-level quantification of total disease burden (SUV_total) and metabolic tumor volume (MTV) was assessed using Spearman’s correlation coefficients between the segmentation output and physician contours. Lesion segmentation and patient quantification performance was compared to inter-physician agreement in a subset of 20 patients segmented by a second nuclear medicine physician. In total, 1223 lesions with median tumor-to-background ratio of 4.0 and volume of 1.8 cm³, were evaluated. When assessed for lesion segmentation, a 3D CNN, DeepMedic, achieved the highest performance across all evaluation metrics. DeepMedic, clustering methods, and an iterative threshold method had lesion-level segmentation performance comparable to the degree of inter-physician agreement. For patient-level SUV_total and MTV quantification, all methods except 40% and 50% SUV_max and adaptive region-growing achieved a performance that was similar the agreement of the two physicians. Multiple methods, including a 3D CNN, clustering, and an iterative threshold method, achieved both good lesion-level segmentation and patient-level quantification performance in a population of 90 lymphoma patients. These methods are thus recommended over thresholding methods such as 40% and 50% SUV_max, which were consistently found to be significantly outside the limits defined by inter-physician agreement. (paper)

[en] Highlights: • Metabolic changes on FDG PET/CT offer an earlier response evaluation than MRI. • PET/CT is less sensitive than MRI for diffuse bone marrow involvement. • PET/CT is a highly sensitive modality to determine extra-medullary disease. • Red marrow expansion: false positive findings on both FDG PET/CT and MRI. • Compression fractures are best characterized with MRI. - Abstract: 18-Flurodeoxyglucose Positron Emission Tomography with computed tomography (FDG PET/CT) and Magnetic Resonance Imaging (MRI) have higher sensitivity and specificity than whole-body X-ray (WBXR) survey in evaluating disease extent in patients with multiple myeloma (MM). Both modalities are now recommended by the Durie–Salmon Plus classification although the emphasis is more on MRI than PET/CT. The presence of extra-medullary disease (EMD) as evaluated by PET/CT imaging, initial SUV_m_a_x and number of focal lesions (FL) are deemed to be strong prognostic parameters at staging. MRI remains the most sensitive technique for the detection of diffuse bone marrow involvement in both the pre and post-therapy setting. Compression fractures are best characterized with MRI signal changes, for determining vertebroplasty candidates. While PET/CT allows for earlier and more specific evaluation of therapeutic efficacy compared to MRI, when signal abnormalities persist years after treatment. PET/CT interpretation, however, can be challenging in the vertebral column and pelvis as well as in cases with post-therapy changes. Hence, a reading approach combining the high sensitivity of MRI and superior specificity of FDG PET/CT would be preferred to increase the diagnostic accuracy. In summary, the established management methods in MM, mainly relying on biological tumor parameters should be complemented with functional imaging data, both at staging and restaging for optimal management of MM

[en] Purpose: To correlate positron emission tomography (PET) standard uptake value (SUV) with pathologic specimen size in patients with head-and-neck cancers. Methods and Materials: Eighteen patients with Stage II-IVB head-and-neck cancer with 27 tumors who underwent PET and computed tomography (CT) imaging of the head and neck followed by surgical resection were selected for this study. Various SUV thresholds were examined, including the software default (SUV_def), narrowing the window by 1 standard deviation (SD) of the maximum (SUV-1SD), and SUV cutoff values of 2.5 or greater (SUV2.5) and 40% or greater maximum (SUV40). Volumetric pathologic data were available for 12 patients. Tumor volumes based on pathologic examination (gold standard), CT, SUV_def, SUV-1SD, SUV2.5, and SUV40 were analyzed. Results: PET identified five tumors not seen on CT. The sensitivity of PET for identifying primary tumors was 94% (17 of 18). The Sensitivity of PET for staging the neck was 90% (9 of 10), whereas the specificity was 78% (7 of 9). The SUV2.5 method was most likely to overestimate tumor volume, whereas SUV_def and SUV-1SD were most likely to underestimate tumor volume. Conclusions: The PET scan provides more accurate staging of primary tumors and nodal metastases for patients with advanced head-and-neck cancer than CT alone. Compared with the gold standard, significant variability exists in volumes obtained by using various SUV thresholds. A combination of clinical, CT, and PET data should continue to be used for optimal treatment planning. The SUV40 method appears to offer the best compromise between accuracy and reducing the risk of underestimating tumor extent