Long-term metabolic evolution of brain metastases with suspected radiation necrosis following stereotactic radiosurgery: longitudinal assessment by F-DOPA PET.

BACKGROUND: The evolution of radiation necrosis (RN) varies depending on the combination of radionecrotic tissue and active tumor cells. In this study, we characterized the long-term metabolic evolution of RN by sequential PET/CT imaging with 3,4-dihydroxy-6-[18F]-fluoro-l-phenylalanine (F-DOPA) in patients with brain metastases following stereotactic radiosurgery (SRS). METHODS: Thirty consecutive patients with 34 suspected radionecrotic brain metastases following SRS repeated F-DOPA PET/CT every 6 months or yearly in addition to standard MRI monitoring. Diagnoses of local progression (LP) or RN were confirmed histologically or by clinical follow-up. Semi-quantitative parameters of F-DOPA uptake were extracted at different time points, and their diagnostic performances were compared with those of corresponding contrast-enhanced MRI. RESULTS: Ninety-nine F-DOPA PET scans were acquired over a median period of 18 (range: 12-66) months. Median follow-up from the baseline F-DOPA PET/CT was 48 (range 21-95) months. Overall, 24 (70.6%) and 10 (29.4%) lesions were classified as RN and LP, respectively. LP occurred after a median of 18 (range: 12-30) months from baseline PET. F-DOPA tumor-to-brain ratio (TBR) and relative standardized uptake value (rSUV) increased significantly over time in LP lesions, while remaining stable in RN lesions. The parameter showing the best diagnostic performance was rSUV (accuracy = 94.1% for the optimal threshold of 1.92). In contrast, variations of the longest tumor dimension measured on contrast-enhancing MRI did not distinguish between RN and LP. CONCLUSION: F-DOPA PET has a high diagnostic accuracy for assessing the long-term evolution of brain metastases following SRS.

Metabolic Evolution of Brain Metastasis After Stereotactic Radiosurgery: Mismatch Between F-DOPA and FDG PET.

The differentiation between radiation-induced changes and tumor recurrence is a major pitfall of magnetic resonance imaging, which can be overcome by the use of PET. Although amino-acid PET tracers showed several advantages over F-fluorodeoxyglucose in neurooncology, studies comparing these 2 types of radiopharmaceuticals in previously irradiated brain metastases are lacking. Here, we demonstrated a mismatch between 3,4-dihydroxy-6-[F]-fluoro-L-phenylalanine (F-DOPA) and FDG in the first report of a previously irradiated brain metastasis undergoing a longitudinal evaluation by sequential double tracer PET imaging.

18F-DOPA uptake does not correlate with IDH mutation status and 1p/19q co-deletion in glioma.

OBJECTIVE: The role of amino acid positron emission tomography (PET) in glioma grading and outcome prognostication has not yet been well established. This is particularly true in the context of the new WHO 2016 classification, which introduced a definition of glioma subtypes primarily based on molecular fingerprints. The aim of the present study was to correlate 3,4­dihydroxy­6­[18F]­fluoro-L­phenylalanine (F-DOPA) uptake parameters with IDH mutation, 1p/19q status, and survival outcomes in patients with glioma. METHODS: The study population consisted of 33 patients (17 M/16 F, mean age: 46 ± 13 years) who underwent F-DOPA PET/CT for the evaluation of tumor extent before the start of chemo or radiotherapy. The presence of IDH mutation and 1p/19q status was assessed in all the cases. Tumor volume and semiquantitative uptake parameters, namely SUVmax, tumor-to-normal brain ratio and tumor-to-normal striatum ratio, were calculated for each tumor. Imaging-derived parameters were compared between patients stratified according to molecular fingerprints, using parametric or non-parametric tests, where appropriate. The Kaplan-Meier method was used to assess differences of overall survival (OS) and progression-free survival (PFS) between groups. PET parameters were also tested as prognostic factors in univariate Cox survival regression models. RESULTS: There were 12 IDH-wild-type and 21 IDH-mutant patients. Stratification according to 1p/19q co-deletion resulted in 20 non-co-deleted and 13 co-deleted patients. Median follow-up time from PET/CT exam was 30.5 months (range 3.5-74 months). Semiquantitative uptake parameters did correlate neither with IDH mutation nor with 1p/19q status. Uptake was similar in low-grade and high-grade tumors, respectively. In addition, F-DOPA uptake parameters, macroscopic tumor volume, or tumor grade did not stratify OS, while a correlation between SUVmax and PFS was shown in the subgroup of astrocytomas. On the other hand, IDH mutation status and presence of 1p/19q co-deletion had a significant impact on survival outcomes. The prognostic value of IDH mutation status was also confirmed in the subgroup of patients with astrocytic tumors. CONCLUSIONS: F-DOPA uptake parameters do not correlate with tumor molecular and histological characteristics. The predictive value of PET-derived parameters on outcomes of survival is limited.

Clinical Usefulness of 18F-Fluorodeoxyglucose Positron Emission Tomography in the Diagnostic Algorithm of Advanced Entero-Pancreatic Neuroendocrine Neoplasms.

BACKGROUND: The role of 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) in the diagnostic algorithm of entero-pancreatic neuroendocrine neoplasms (EP NENs) is unclear because most available data derive from heterogeneous populations in terms of tumor biology and disease status at time of examination. The aim of this study was to determine the ability of 18F-FDG PET to identify patients with more aggressive disease among those with advanced EP NENs. Subjects, Materials, and Methods . Patients with advanced EP NENs and known disease status (progressive disease [PD] or stable disease [SD]) according to imaging procedures, who received 18F-FDG PET and computed tomography scans during a time frame of 1 month, were included. RESULTS: A total of 93 patients, including 69 patients with pancreatic NENs and 24 patients with small-intestine NENs, were included. At the time of study entry, 64 patients (68.8%) had PD, and the remaining 29 patients (31.2%) had SD. A total of 62 patients (66.7%) had positive 18F-FDG PET, whereas 18F-FDG PET was negative in the remaining 31 patients (33.3%). Overall, 18F-FDG PET sensitivity and specificity to detect PD were 90.6% and 86.2%, respectively, resulting in a diagnostic accuracy of 89.2%. A positive 18F-FDG PET was significantly associated with PD at the time of study entry (p < .0001 at multivariate analysis). Although a higher proportion of 18F-FDG PET-positive examinations were observed in patients with higher tumor grade (p = .01), 53.8% of patients with grade 1 neuroendocrine tumors (NETs) had positive 18F-FDG PET, and 37.5% of patients with grade 2 NETs had negative 18F-FDG PET. Overall survival was significantly shorter in 18F-FDG PET-positive patients (median: 60 months) in comparison with 18F-FDG PET-negative patients (median not reached; p = .008). CONCLUSION: 18F-FDG PET has a high diagnostic accuracy to identify progression of disease with unfavorable clinical outcome in patients with advanced EP NENs. Knowledge of disease status and G grading are key factors for physicians to better select patients for whom 18F-FDG PET is clinically useful. IMPLICATIONS FOR PRACTICE: The findings of the present study may help physicians dealing with advanced neuroendocrine neoplasms to select patients for whom 18F-fluorodeoxyglucose positron emission tomography is useful to predict poor clinical outcome.

18F-DOPA uptake parameters in glioma: effects of patients' characteristics and prior treatment history.

OBJECTIVE: In amino acid positron emission tomography brain tumour imaging, tumour-to-background uptake parameters are often used for treatment monitoring. We studied the effects of patients' characteristics and anticancer treatments on 18F-fluoro-l-phenylalanine uptake of normal brain and tumour lesions, with particular emphasis on temozolomide (TMZ) chemotherapy. METHODS: 155 studies from 120 patients with glioma were analysed. Average uptake of normal background (standardized uptake value, SUVbckgr) and basal ganglia (SUVbg), as well as tumour-to-brain ratios (TBR) were compared between positron emission tomography/CT studies acquired before (Group A, n = 48), after (Group B, n = 50) or during (Group C, n = 57) TMZ treatment, using analysis of variance. RESULTS: Overall, mean SUVbckgr and mean SUVbg were 1.06 ± 0.26 and 2.12 ± 0.47, respectively. Female had significantly higher SUVbckgr (p = 0.002) and SUVbg (p = 0.012) than male patients. Age showed a positive correlation with SUVbg (p = 0.001). In the overall cohort, there were significant effects of TMZ on SUVbckgr (p = 0.0237) and TBR (p = 0.0138). In particular, SUVbckgr was lower in Group C than in Group B (1.00 ± 0.25 vs 1.14 ± 0.31, p = 0.0173). Significant variations of SUVbckr could be observed in female only. TBR was significantly higher in Group C than in Group B (2.37 ± 0.54 vs 2.06 ± 0.38, p = 0.010). Variations of SUVbg between groups slightly missed significance (p = 0.0504). CONCLUSION: Temozolomide chemotherapy and patients' characteristics, including gender and age, affect physiological [18F]-fluoro-l-phenylalanine uptake and, consequently, the calculation of TBRs. Advances in knowledge: For the first time, the effects of past or concurrent temozolomide chemotherapy on brain physiological amino acid uptake have been investigated. Such effects are relevant and should be taken into account when evaluating tumour-to-background ratios.

(18)F-DOPA Positron Emission Tomography in Medulloblastoma: 2 Case Reports.

BACKGROUND: Medulloblastoma (MDB) is an aggressive embryonal brain tumor, with underlying altered genetics and biological pathways that account for very heterogeneous natural histories and clinical behaviors. Positron emission tomography (PET) using radiolabeled amino acids provides important metabolic information for the diagnosis of cerebral glioma but only a few data are available on amino acid PET in MDB. In particular, no cases of MDB imaging with 6-[(18)F]-fluoro-L-3,4-dihydroxyphenylalanine (F-DOPA) have previously been described. CASE DESCRIPTION: Two patients with different histologic subtypes of MDB were referred for F-DOPA PET to define the extent and metabolic degree of their diseases. The patients had a newly diagnosed large-cell/anaplastic MDB and a fourth relapse of classic MDB, respectively. F-DOPA PET was unremarkable in the first case; F-DOPA uptake was low in the second patient with the tumor/background ratio as high as 1.29. Comparison was made with magnetic resonance imaging, which showed fluid-attenuated inversion recovery positive diseases. Aggressive tumor growth was shown in the clinical course of both patients. CONCLUSIONS: The 2 cases reported here suggest that sensitivity of F-DOPA PET in MDB can be low. However, more comprehensive data are needed to conclude on the overall accuracy of F-DOPA PET in MDB.

Molecular response assessed by (68)Ga-DOTANOC and survival after (90)Y microsphere therapy in patients with liver metastases from neuroendocrine tumours.

PURPOSE: We investigated the prognostic role of (68)Ga-DOTANOC in patients affected by hepatic metastases from neuroendocrine tumours (NET) undergoing (90)Y radioembolization ((90)Y-RE). METHODS: A group of 15 consecutive patients with unresectable NET liver metastases underwent (68)Ga-DOTANOC PET at baseline and 6 weeks after (90)Y-RE. Molecular response was defined as a reduction of >50% in the tumour-to-spleen ratio (ΔT/S). The patients were divided into two groups (responders with ΔT/S >50% and nonresponders with ΔT/S <50%) Patients were followed up by imaging and laboratory tests every 3 months until death or for at least 36 months following (90)Y-RE. Statistical analysis was performed to identify factors predicting overall survival (OS) and progression-free survival (PFS). RESULTS: A decrease in T/S ratio was seen in all patients on (68)Ga-DOTANOC PET scans performed after (90)Y-RE. Nine patients were classified as responders and six as nonresponders. The mean OS in all patients was 31.0 months. Responders had a significantly (p < 0.001) longer OS (mean 36.0 ± 2.5 months) and PFS (mean 29.7 ± 3.4 months) than nonresponders. In a multivariate analysis, none of the other examined variables including age, unilobar vs. bilobar locations, bilirubin levels, radiological response or the presence of extrahepatic disease significantly predicted patient outcome. CONCLUSION: Molecular response assessed with (68)Ga-DOTANOC PET might be a useful predictor of survival in patients affected by NET liver metastases treated with (90)Y-RE.

In vivo evaluation of TNF-alpha in the lungs of patients affected by sarcoidosis.

INTRODUCTION: Sarcoidosis is a multisystemic granulomatous disorder characterized by multiple noncaseating granulomas involving intrathoracic lymph nodes and lung parenchyma. Recently, the use of anti-tumor necrosis factor alpha (anti-TNFα) agents has been introduced for therapy of chronic and refractory sarcoidosis with controversial results. Infliximab (Remicade) is a chimeric monoclonal antibody (mAb) that recognizes and binds TNFα, neutralizing its biological effects. In the present study, (99m)Tc labelled infliximab was used to study the expression of TNFα in sarcoid lesions and to evaluate its role as a predictive marker in response to therapy with Remicade. MATERIAL AND METHODS: A total of 10 patients with newly diagnosed sarcoidosis were enrolled together with 10 control patients affected by rheumatoid arthritis. All patients were studied by planar imaging of the chest with (99m)Tc-infliximab at 6 h and 24 h and total body [(18)F]-FDG PET/CT. Regions of interest were drawn over the lungs and the right arm and target-to-background ratios were analysed for (99m)Tc-infliximab. SUV mean and SUV max were calculated over lungs for FDG. RESULTS AND DISCUSSION: Image analysis showed low correlation between T/B ratios and BAL results in patients despite positivity at [(18)F]-FDG PET. CONCLUSION: In conclusion, patients with newly diagnosed pulmonary sarcoidosis, with FDG-PET and BAL positivity, showed a negative (99m)Tc-infliximab scintigraphy.

Volumetric assessment of recurrent or progressive gliomas: comparison between F-DOPA PET and perfusion-weighted MRI.

PURPOSE: To compare the diagnostic information obtained with 6-[(18)F]-fluoro-L-3,4-dihydroxyphenylalanine (F-DOPA) PET and relative cerebral blood volume (rCBV) maps in recurrent or progressive glioma. METHODS: All patients with recurrent or progressive glioma referred for F-DOPA imaging at our institution between May 2010 and May 2014 were retrospectively included, provided that macroscopic disease was visible on conventional MRI images and that rCBV maps were available for comparison. The final analysis included 50 paired studies (44 patients). After image registration, automatic tumour segmentation of both sets of images was performed using the average signal in a large reference VOI including grey and white matter multiplied by 1.6. Tumour volumes identified by both modalities were compared and their spatial congruence calculated. The distances between F-DOPA uptake and rCBV hot spots, tumour-to-brain ratios (TBRs) and normalized histograms were also computed. RESULTS: On visual inspection, 49 of the 50 F-DOPA and 45 of the 50 rCBV studies were classified as positive. The tumour volume delineated using F-DOPA (F-DOPAvol 1.6) greatly exceeded that of rCBV maps (rCBVvol 1.6). The median F-DOPAvol 1.6 and rCBVvol 1.6 were 11.44 ml (range 0 - 220.95 ml) and 1.04 ml (range 0 - 26.30 ml), respectively (p < 0.00001). Overall, the median overlapping volume was 0.27 ml, resulting in a spatial congruence of 1.38 % (range 0 - 39.22 %). The mean hot spot distance was 27.17 mm (±16.92 mm). F-DOPA uptake TBR was significantly higher than rCBV TBR (1.76 ± 0.60 vs. 1.15 ± 0.52, respectively; p < 0.0001). The histogram analysis showed that F-DOPA provided better separation of tumour from background. In 6 of the 50 studies (12 %), however, physiological uptake in the striatum interfered with tumour delineation. CONCLUSION: The information provided by F-DOPA PET and rCBV maps are substantially different. Image interpretation is easier and a larger tumour extent is identified on F-DOPA PET images than on rCBV maps. The clinical impact of such differences needs to be explored in future studies.

Change in total lesion glycolysis and clinical outcome after (90)Y radioembolization in intrahepatic cholangiocarcinoma.

INTRODUCTION: Our aim was to assess the prognostic value of post-treatment decrease in total lesion glycolysis (ΔTLG) assessed by 2-[(18)F]-fluorodeoxyglucose ([(18)F] FDG) PET-CT performed 6weeks after (90)Y radioembolization ((90)Y RE) in patients affected by intrahepatic cholangiocarcinoma (ICC). METHODS: A total of 18 patients were accepted into our department for (90)Y RE. Before the procedure, all patients underwent [(18)F] FDG PET-CT, and total lesion glycolysis was calculated. Six weeks after (90)Y administration, PET scan was performed, and ΔTLG was determined. Patients underwent follow up by imaging and laboratory at quarterly intervals until death or for at least 24 months from (90)Y RE. Furthermore, subjects were divided in 2 groups (group 1: 6 weeks ΔTLG>50%, group 2: ΔTLG<50%). Kaplan-Meier method was used to achieve time to progression (TTP) and overall survival (OS) curves for each group. TTP and OS curves were compared to demonstrate eventual relevant differences between the 2 groups. RESULTS: Seventeen patients underwent (90)Y RE, and one subject was considered ineligible. According to PET Response Criteria in Solid Tumors, partial response was found in 14 patients (82.4%), stable disease in 3 (17.6%). No patient showed complete metabolic response. The mean OS for all patients was 64.5±5.0 weeks. Subjects with a ΔTLG>50% and ΔTLG<50% had a mean OS of 79.6±3.6 and 43.1±2.0 weeks, respectively (p<0.001). TTP resulted of 28.9±3.8 weeks for the whole cohort. Patients with ΔTLG>50% had a significantly longer TTP (mean 36.9±3.6 weeks) than those with ΔTLG<50% (mean 13.7±1.7 weeks, p=0.001). CONCLUSION: Our results indicate that (90)Y RE can be an effective and safe therapy for ICC. ΔTLG calculated on post-treatment [(18)F] FDG PET-CT agrees with patients' final outcome.

Thyro-gastric autoimmunity in patients with differentiated thyroid cancer: a prospective study.

Thyro-gastric autoimmunity has not been previously evaluated in patients with differentiated thyroid cancer (DTC), although its long-term complications may be relevant for the management of DTC patients. We assessed the prevalence of gastric autoimmunity and autoimmune gastritis (AG) in patients with Hashimoto's thyroiditis (HT) and concomitant DTC. Prevalence of parietal cell antibody (PCA) positivity, iron deficiency anemia (IDA), and pernicious anemia (PA) were prospectively assessed in 150 DTC patients referred for radioiodine ablation after total thyroidectomy. Patients were classified as HT (n = 31) and non-HT (n = 119) based on a combination of serological, ultrasonographic, and histological findings. Patients with PCA positivity were subsequently addressed to endoscopy for confirmation of atrophy body gastritis, required for the diagnosis of AG. For all the variables under study, a comparison between groups was made using Fisher's exact test and appropriate parametric and non-parametric tests. PCA positivity was significantly more prevalent in HT than in non-HT patients (12.9 vs 1.6 %, p = 0.017). After Hp eradication, a reversal of PCA positivity was observed in 3/4 patients in the HT group. IDA and PA did not differ significantly between groups. In the HT group, only one patient had endoscopical confirmation of mild gastric corporal atrophy. Gastric autoimmunity shows higher prevalence in patients with DTC and concomitant HT than in patients with DTC alone; however, in most cases, PCA positivity was associated with Hp infection. Furthermore, although previous reports found up to one-third of patients with HT to have associated AG, in our cohort AG was extremely rare.

Accuracy of F-DOPA PET and perfusion-MRI for differentiating radionecrotic from progressive brain metastases after radiosurgery.

PURPOSE: We assessed the performance of 6-[(18)F]-fluoro-L-3,4-dihydroxyphenylalanine (F-DOPA) PET for differentiating radionecrosis (RN) from tumour progression (PD) in a population of patients with brain metastases, treated with stereotactic radiosurgery. The accuracy of F-DOPA PET was compared with that of perfusion-weighted magnetic resonance (perfusion-MR). METHODS: In 42 patients with a total of 50 brain metastases from various primaries F-DOPA PET/CT was performed because of suspected radiological progression at the site of previously irradiated brain metastasis. Several semiquantitative PET parameters were recorded, and their diagnostic accuracy was compared by receiver operating characteristic curve analyses. The diagnosis was established by either surgery or follow-up. A comparison was made between F-DOPA PET and perfusion-MR sequences acquired no more than 3 weeks apart. RESULTS: Definitive outcome was available in 46 of the 50 lesions (20 PD, 26 RN). Of the 46 lesions, 11 were surgically excised while in the remaining 35 lesions the diagnosis was established by radiological and clinical criteria. The best diagnostic performance was obtained using the semiquantitative PET parameter maximum lesion to maximum background uptake ratio (SUVLmax/Bkgrmax). With a cut-off value of 1.59, a sensitivity of 90 % and a specificity of 92.3 % were achieved in differentiating RN from PD lesions (accuracy 91.3 %). Relative cerebral blood volume (rCBV) derived from perfusion-MR was available for comparison in 37 of the 46 metastases. Overall accuracy of rCBV was lower than that of all semiquantitative PET parameters under study. The best differentiating rCBV cut-off value was 2.14; this yielded a sensitivity of 86.7 % and a specificity of 68.2 % (accuracy 75.6 %). CONCLUSION: F-DOPA PET is a highly accurate tool for differentiating RN from PD brain metastases after stereotactic radiosurgery. In this specific setting, F-DOPA PET seems to perform better than perfusion-MR.

High-resolution, handheld camera use for occult breast lesion localization plus sentinel node biopsy (SNOLL): a single-institution experience with 186 patients.

BACKGROUND: Sentinel node and occult lesion localization (SNOLL) calls for a combination of two specific procedures: intraoperative detection of sentinel lymph node (SLN) via gamma probe and radioguided occult lesion localization (ROLL). This applies to nonpalpable invasive breast cancer or high-grade in situ carcinoma. As opposed to standard techniques, today's handheld gamma cameras enable intraoperative scintigraphic images. METHODS: A cohort (N = 186) of consecutive patients with breast cancer was subjected to radioguided conservative surgery (quadrantectomy and SLN biopsy), using a standard gamma probe and a high-resolution handheld camera. Intraoperative SLN frozen section was also performed. RESULTS: Neoplastic lesions were removed in 99.4% of all patients, and SLN biopsy was achieved in 99%. Of the 137 patients with invasive cancer, SLN metastasis was confirmed in 21. In 12% of patients, a second operation was required for close or tumor-positive surgical margins. DISCUSSION: This combination of procedures represents an improvement in the surgical management of occult breast carcinomas and is the method of choice for accurate tumor localization and SLN biopsy. Handheld cameras have the potential to become highly useful intraoperative aids.

Tumor thrombus in the renal vein from an adrenal metastasis of lung cancer: 18FDG PET/CT findings.

Tumor thrombus is a rare complication of solid cancer. The authors report a case of a 76-year-old woman presenting a thick walled cystic mass in the lower lobe of the left lung. 18FDG positron emission tomography (PET)/computed tomography (CT) was performed, showing tracer accumulation in the wall of the pulmonary lesion and in the mediastinal and hilar lymph nodes. Moreover, PET/CT depicted a gross mass in the left adrenal gland and a hypermetabolic focus corresponding to the anatomic location of the left renal vein. Contrast-enhanced CT, subsequently performed, confirmed PET findings in the lung, lymph nodes, and adrenal glands, also demonstrating marginal enhancement and intraluminal filling defect in the left renal vein, which was interpreted as tumor thrombus due to the 18FDG uptake at PET scan. CT-guided biopsy of the mass was positive for poorly differentiated carcinoma. 18FDG PET can be useful to diagnose tumor thrombus in oncological patients.

(18)F-FDG PET/CT imaging of massive portal vein tumor thrombosis from ileal adenocarcinoma.

A 72 years old patient was referred to us with ileal adenocarcinoma after surgical desection. Fluorine-18- fluorodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG PET/CT) imaging showed massive portal vein, tumor thrombosis. Clinical examination and laboratory tests did not support the diagnosis of septic thrombus. To the best of our knowledge, this is the first reported case in the literature of a massive tumor thrombus in the right portal system from ileal carcinoma, detected by (18)F-FDG PET/CT.

Hemodialysis in patients requiring 131I treatment for thyroid carcinoma.

PURPOSE: Thyroid malignancies can be treated by surgery followed by ablation of the remnant tissue with 131I. As iodide removal from the body occurs by renal extraction, in patients suffering from end-stage renal disease it is necessary to properly evaluate both timing and method of the extracorporeal treatment.
 METHODS: We present two patients on regular hemodialysis, admitted in isolation to the Nuclear Medicine Department and treated with 131I for thyroid carcinoma diagnosed during the check-up for transplantation. Both patients underwent two hemodialysis sessions with a portable machine for CRRT (continuous renal replacement therapy), 24 and 48 hours after the administration of 50 mCi of 131I. The nursing staff were monitored with a dosimeter. Radioactivity of the patients, dialysate and urines were measured during hemodialysis. 
 RESULTS: The greater reduction was obtained with the first dialysis, but in both patients a further, though shorter, hemodialysis at 48 hours was necessary for reaching a patient's radioactivity compatible with discharge. Radioactivity measured in the dialysate demonstrated the almost total removal of radioiodine by dialysis alone. In both patients, follow-up exams revealed a complete ablation of thyroid tissue, without signs of local recurrence. The dose of radioactivity of the dialysis staff was below allowable limits. 
 CONCLUSIONS: We conclude that a successful reduction of radioactivity, without dispersing its therapeutic efficacy, can be obtained with daily hemodialysis with a CRRT machine in patients in isolation treated with 131I. A therapeutic model is proposed.

Absorbed dose to lesion and clinical outcome after liver radioembolization with 90Y microspheres: a case report of PET-based dosimetry.

A 54-year-old woman with metastatic colorectal carcinoma underwent liver radioembolization with (90)Y resin microspheres. Microsphere biodistribution was assessed 2 h after the treatment through a 20-min long (90)Y PET scan. Isodose map and lesion dose-volume histogram (DVH) were then evaluated using a MATLAB-based code. Response to therapy was assessed performing a (18)F-FDG PET 6 months after the treatment. At (90)Y PET the patient showed a well-defined horseshoe-shaped hepatic lesion with hot margins and a cold core. The lesion presented a heterogeneous DVH with a hot margin receiving an average radiation dose as high as 287 Gy and a cold area receiving an average radiation dose of 70 Gy approximately. Six months after the treatment the patient reported a complete remission of tumour areas which received a high radiation dose, while progression of metastases was observed in the area that presented scarce microsphere localization at (90)Y PET. According to our experience, the use of (90)Y PET voxel dosimetry may provide a useful tool to assess possible correlations between microsphere biodistribution and clinical outcome of the treatment. In agreement with current literature findings, an average radiation dose greater than approximately 100 Gy may be required to sterilize liver metastases.