Changes in the concept and practice of radioembolization (SIRT).

The experience gained through the practice of radioembolization (SIRT) results in improvement of clinical outcomes. Improved outcomes are a prerequisite for the clinicians to reffer patients for SIRT. In recent years there are some critical changes in the concept and practice of SIRT that also contribute to the improvement of clinical outcomes, beyond the experience of the center performing SIRT. Two of them are dosimetry and a trend toward more focused therapies in the form of radiation lobectomy or segmentectomy.

Automatic characterization of myocardial perfusion imaging polar maps employing deep learning and data augmentation.

OBJECTIVE: To investigate a deep learning technique, more specifically state-of-the-art convolutional neural networks (CNN), for automatic characterization of polar maps derived from myocardial perfusion imaging (MPI) studies for the diagnosis of coronary artery disease. SUBJECTS AND METHODS: Stress and rest polar maps corresponding to 216 patient cases from the database of the department of Nuclear Medicine of our institution were analyzed. Both attenuation-corrected (AC) and non-corrected (NAC) images were included. All patients were subjected to invasive coronary angiography within 60 days from MPI. As the initial dataset of this study was small to train a deep learning model from scratch, two strategies were followed. The first is called transfer learning. For this, we employed the state-of-the-art CNN called VGG16, which has been broadly exploited in medical imaging classification tasks. The second strategy involves data augmentation, which is achieved by the rotation of the polar maps, to expand the training set. We evaluated VGG16 with 10-fold cross-validation on the original set of images performing separate experiments for AC and NAC polar maps, as well as for their combination. The results were compared to the standard semi-quantitative polar map analysis based on summed stress and summed difference scores, as well as to the medical experts' diagnostic yield. RESULTS: With reference to the findings of coronary angiography, VGG16 achieved an accuracy of 74.53%, sensitivity 75.00% and specificity 73.43% when the AC and NAC polar maps were incorporated into one single image set. Respective figures of MPI interpretation by experienced Nuclear Medicine physicians were 75.00%, 76.97% and 70.31%. The accuracy of semi-quantitative polar map analysis was lower, 66.20% and 64.81% for AC and NAC technique, respectively. CONCLUSION: The proposed deep learning model with data augmentation techniques performed better than the conventional semi-quantitative polar map analysis and competed with doctor's expertise in this particular patient cohort and image set. The model could potentially serve as an assisting tool to support interpretation of MPI studies or could be used for teaching purposes.

90Y-microsphere radioembolization: The method, clinical evidence and perspective.

The current review unfolds the procedural steps and the clinical evidence for yttrium-90 (90Y)-microspheres radioembolization. Radioembolization is part of the loco-regional therapeutic spectrum for liver malignancy and involves the invasive, intra-arterial delivery of microspheres carrying ß-emitter isotopes in order to destroy cancerous tissue via ionizing radiation. The main steps of the therapeutic process are selection of eligible patients, angiographic workup, simulation scintigraphy, pre-treatment dosimetry, actual treatment and post-treatment imaging/dosimetry. Radioembolization is routinely applied in advanced stage hepatocellular carcinoma (HCC), yet its role is being investigated even in earlier stages. Prospective, randomized controlled trials did not verify increased overall survival of radioembolization over systemic treatment with sorafenib in HCC; however, it showed survival benefit in certain sub-groups and a favorable toxicity profile with fewer adverse events. Radioembolization is also applied in metastatic colon cancer showing tumoral liver responses, which however did not translate into an overall survival benefit. Data regarding applications of this method in other neoplasms, such as neuroendocrine tumors, breast cancer and melanoma are also presented. There are ongoing clinical trials to define the role of radioembolization within recent treatments algorithms, to determine optimal combinations of this treatment with systemic and targeted therapies and to decide the patients' sub-groups, who will benefit the most.

Whole body bone SPET/CT can successfully replace the conventional bone scan in breast cancer patients. A prospective study of 257 patients.

OBJECTIVE: Single photon emission tomography/computed tomography (SPET/CT) is usually recommended after ambiguous whole body bone scan (WBS) findings. We investigated the value of routine 2-field ("near" whole-body) SPET/CT application in breast cancer (BC) patients. SUBJECTS AND METHODS: In this prospective study planar WBS and 2-field SPET/CT was performed in 257 consecutive BC patients referred for a bone scan. Whole body scan and SPET/CT were interpreted separately. Additional imaging studies and clinical follow-up for 30±24 months elucidated uncertain findings. RESULTS: Bone metastases were confirmed in 65 patients (25.3%). Sensitivity, specificity, accuracy, positive and negative predictive value per-patient was 63.1%, 81.3%, 76.7%, 53.2% and 86.7% for WBS and 96.9%, 87.5%, 89.9%, 72.4% and 98,8% for SPET/CT; differences were statistically significant except for specificity. Respective values of sensitivity per-lesion were 47.6% and 98.9% (P<0.001). Eleven percent of true positive findings were noticed only in the low-dose CT images, while 7% only in SPET. Single photon emission tomography/CT exhibited higher specificity than WBS in the spine (94.8% vs. 88.7%, P=0.04). Whole body scan interpretation changed after SPET/CT in 74 (28.8%) patients. Thirty-two patients with positive/suspicious WBS turned to be metastases-free after the interpretation of SPET/CT while 42 with unremarkable WBS turned to be positive/suspicious. Of these cases, metastases were confirmed in one with negative and 23 with positive/suspicious SPET/CT. The SPET/CT results prompted treatment plan changes in 23 cases (8.9%). CONCLUSION: Whole-body bone SPET/CT scan outperformed WBS in terms of sensitivity, accuracy, positive and negative predictive value and impacted on patient management. Therefore, its use is recommended as a routine procedure in BC patients, even after a negative WBS.

The impact of transmission-emission misregistration on the interpretation of SPET/CT myocardial perfusion studies and the value of misregistration correction.

OBJECTIVE: Previous studies indicate that the quality of single photon emission tomography/computed tomography (SPET/CT) myocardial perfusion imaging (MPI) is degraded by even mild transmission-emission misregistrations. The purpose of the current study was to investigate the impact of SPET/CT misalignment on the interpretation of MPI and examine the value of a commercial software application for registration correction. SUBJECTS AND METHODS: A total of 255 technetium-99m ((99m)Tc)-tetrofosmin stress/rest MPI examinations in 150 patients were reviewed for SPET/CT misalignment. After registration correction by the software, images were reassessed for interpretation differences from the misregistered study. The diagnostic benefit of reregistration was determined by taking into account the non-attenuation compensated image pattern, combined stress-rest evaluation, gated-SPET data and patient's history. In a phantom experiment and in 3 representative clinical cases, SPET/CT misalignment was purposely created by the software by sequential slice shifts and its effect was evaluated quantitatively. RESULTS: Misregistration ≥1 pixel in at least one direction was observed in 24% of studies. Interpretation of MPI changed after registration correction in 11% of cases with misalignment <1 pixel, in 18% with 1-2 and in 73% with ≥2 pixels. The diagnostic information seemed to improve after registration correction in 58% of studies irrespective of the degree of misregistration. Software-simulated misregistration had dissimilar effects in the phantom and the 3 selected clinical cases. CONCLUSIONS: The impact of SPET/CT misregistration on MPI interpretation although influenced by the degree and direction of slice misplacement, it is also case-specific and hardly predictable. Registration restoration by the software seems worthwhile regardless of misregistration magnitude.

CT-based attenuation correction in Tl-201 myocardial perfusion scintigraphy is less effective than non-corrected SPECT for risk stratification.

BACKGROUND: Previous studies advocate the use of attenuation correction in myocardial perfusion scintigraphy (MPS) for patient risk stratification. METHODS: Six-hundred and thirty-seven unselected patients underwent Tl-201 MPS by a hybrid SPECT/CT system. Attenuation-corrected (AC) and non-corrected (NAC) images were interpreted blindly and summed stress scores (SSS) were calculated. Study endpoints were all-cause mortality and the composites of death/non-fatal acute myocardial infarction (AMI) and death/AMI/late revascularization. RESULTS: During a follow-up of 42.3 ± 12.8 months 24 deaths, 13 AMIs and 28 revascularizations were recorded. SSS groups formed according to event rate distribution across SSS values were: 0-4, 5-13, >13 for NAC and 0-2, 3-9, >9 for AC. Kaplan-Meier functions were statistically significant between NAC SSS groups for all study endpoints. AC discriminated only between SSS 0-2 and >9 for death/AMI and between 0-2 and 3-9 for death/AMI/revascularization. In the univariate Cox regression abnormal NAC (SSS > 4) was accompanied with much higher hazards ratios than abnormal AC (SSS > 2). In the multivariate model abnormal AC yielded no significance for either endpoint whereas abnormal NAC proved independent from other covariates for the composite endpoints. CONCLUSION: Our results challenge the effectiveness of CT-based AC for risk stratification of patients referred for MPS.

Bone scintigraphy depicts bilateral atypical femoral stress fractures with metachronous presentation, long before a complete fracture occurs.

Atypical femoral fractures (AFF), although rare, are recognized more often during the last decade. They are located in the subtrochanteric region or the femoral shaft, may be bilateral, can evolve to complete fractures after bone overload or minimal trauma and have specific radiological features. The complete fractures have horizontal or slightly oblique configuration accompanied by a medial spike, are non-comminuted, and extend to both cortices. There is also generalized cortical thickening of femoral shaft. Newer evidence suggests that AFF are stress or insufficiency fractures, possibly associated with long-term use of bisphoshonates (BP). AFF can also occur in oncologic patients referred for bone scintigraphy and, in such a case, they should be differentiated from bone metastases. We present here a case with bilateral AFF with metachronous appearance in a female patient with a history of breast cancer and osteoporosis. The first AFF had been depicted on bone scintigraphy 3 years before a complete fracture occurred at this site, but the finding was overlooked. A second bone scan performed shortly after the fracture in order to exclude underlying bone metastases disclosed an additional unsuspected incomplete AFF in the contralateral femur, which was confirmed by radiography. In conclusion, oncologists should consider other causes of bone pain besides bone metastatic disease, and physicians interpreting whole body bone scans of oncologic patients should be aware of the entity of AFF, in order to avoid false positive results and provide early information about an impending complete AFF.

Ablative Radioembolization (SIRT) of a Large Inoperable Renal Cell Carcinoma Invading the Liver That Resulted in Hematuria Control and Complete Necrosis by mRECIST Criteria.

ABSTRACT: We report the successful application of radioembolization (SIRT) in a 77-year-old man with end-stage renal disease on hemodialysis and repeated episodes of macroscopic hematuria due to a large renal cell carcinoma of the right kidney extending to liver segment VI. A compassionate SIRT therapy was performed with resin microspheres through the upper pole renal artery and the feeding segmental artery of liver segment VI. Hematuria was resolved after treatment, and 4 months later, a follow-up CT scan revealed tumor size reduction and complete tumor necrosis (Response Evaluation Criteria in Solid Tumors criteria). Ablative SIRT therapy could be a safe and efficient option in a large inoperable RCC.

99m Tc-DTPA dynamic SPECT/CT renogram in adults: feasibility and diagnostic benefit.

OBJECTIVE: The objective of this study is to investigate the feasibility and potential advantages of 99m Tc-DTPA dynamic single photon emission computed tomography/computed tomography (SPECT/CT) renogram in adults. METHODS: Fifty-five patients aged 19-80 years (mean 56.3) were enrolled. The imaging protocol included: day 1: 99m Tc-DTPA planar renogram, followed by planar 99m Tc-DMSA scan. Day 3: attenuation-corrected dynamic 99m Tc-DTPA SPECT renogram [DSPECT(AC)] and Cr-51 ethylenediamine tetraacetic acid (EDTA) glomerular filtration rate (GFR) calculation. DSPECT(AC) included an initial CT scan followed by 12 consecutive SPECT sessions acquired via continuous-mode acquisition for a total of 24 min. Fast SPECT sequences (1-2 s/projection, 60 projections, every 6°) were obtained for the first 8 min, followed by slower acquisitions (3-4 s/projection) during the rest of the study. Renal activity was measured in the total kidney volume by regions of interest drawn on consecutive transaxial slices of the third SPECT, which were then copied on the whole 12-SPECT series. Corresponding time-activity curves were created. DSPECT(AC) parameters were compared with those of planar renogram. The reference method for split renal function was 99m Tc-DMSA (geometrical mean of anterior and posterior projection counts) and for GFR the Cr-51 EDTA 2-blood sample clearance method. RESULTS: DSPECT(AC) images were of good quality. There was good correlation between renogram parameters (time to peak activity and NORA20) comparing the two techniques ( r  = 0.959 and 0.933, respectively). In 21 cases with >30% absolute difference between the two kidneys, spilt renal function calculation by DSPECT(AC) correlated perfectly ( r  = 0.968) with the reference method, whereas planar renogram was less accurate ( r  = 0.843). Anatomic information provided by nonenhanced CT offered an integrated structural-functional view valuable for final diagnosis. DSPECT(AC) early kidney uptake as a fraction of injected dose correlated better with reference GFR ( r  = 0.789) than the Gates' method ( r  = 0.642). CONCLUSION: 99m Tc-DTPA dynamic SPECT/CT renogram is feasible with conventional SPECT/CT systems. It allows accurate split renal function measurement, offers additional anatomical information and can be used for closer approximation of GFR compared with Gates' method.

Is there a role for Nuclear Medicine in diagnosis and management of patients with primary aldosteronism?

Primary aldosteronism (PA) is the most common cause of secondary hypertension. The diagnosis of PA is of clinical importance for choosing the appropriate treatment, meaning, surgery for the unilateral disease, and inclusion of aldosterone antagonists in the antihypertensive treatment for the bilateral disease. Current diagnostic approaches showed that the prevalence of PA is much higher than previously estimated. There is still controversy regarding the true prevalence of PA in hypertensive patients. The gold standard for differentiating between unilateral and bilateral disease is the adrenal vein sampling (AVS), a method that is invasive and is performed accurately in only few dedicated centers. Non invasive methods (imaging) for discriminating the two entities are: the CT scan, MRI and iodocholesterol (NP-59) scintigraphy performed under dexamethasone suppression. But the accuracy of imaging compared to AVS is suboptimal and can result in wrong therapeutic decisions. NP-59 scintigraphy is a non-invasive functional imaging technique that reveals the adrenal cortical autonomic function and could have of incremental value over anatomical imaging. In conclusion, in previous years NP-59 scintigraphy was used infrequently, but recently with the advent of hybrid single photon emission tomography (SPET/CT) systems the interest in NP-59 scintigraphy has been renewed. Studies comparing NP-59 SPET/CT imaging with AVS are warranted in order to establish its diagnostic accuracy.

ST-segment depression during vasodilator stress is of minor clinical importance in women with normal myocardial perfusion imaging and low or intermediate risk of coronary artery disease.

PURPOSE: The prognostic value of electrocardiographic (ECG) ST-segment depression during vasodilator stress testing in patients with normal myocardial perfusion scintigraphy (MPS) is based on retrospective studies with controversial results. Moreover, the true incidence of obstructive coronary artery disease (CAD) in these patients is unknown. METHODS: During a 33-month period, all consecutive patients referred for MPS were prospectively evaluated for interpretable ST-segment depression ≥ 1 mm during vasodilator stress testing. Of 1,687 patients with normal MPS and without known CAD, 109 (100 women) aged 65.2 ± 9.2 years demonstrated ST-segment shifts and formed the ECG-positive group. The pretest probability of CAD was low in 56%, intermediate in 39% and high in 5%. They were advised to proceed to coronary angiography. An equal number of patients with normal MPS and no ECG abnormalities matched for CAD predisposing factors comprised the control group. Follow-up of both groups was accomplished through a telephone interview. RESULTS: Fifty-two patients from the ECG-positive group (48%) consented to coronary angiography. Six (11.5%) had obstructive CAD (≥50% lumen stenosis), one with left main artery disease, while three required revascularization. Follow-up was complete in 99 ECG-positive patients for a period of 20.6 ± 8.9 months. One hard event (non-fatal myocardial infarction) and one soft event (revascularization) were observed. No event was recorded in the control group. CONCLUSION: In patients with low-intermediate risk of CAD, "ischaemic" ECG changes during vasodilator stress combined with normal MPS are encountered mostly in women and are associated with a low prevalence of significant CAD and a low cardiac event rate.

Inferior myocardial wall ischemia on SPECT-MPI in patients with non dominant right coronary artery and non significant coronary artery disease.

BACKGROUND: The impact of a non-dominant right coronary artery (NDRCA), on single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI)has not been clarified. METHODS AND RESULTS: We compared SPECT-MPI results of consecutive patients without significant (diameter stenosis ≥50%)coronary artery disease (CAD) and a NDRCA (Group-1), with those of patients from our database without CAD and a dominant RCA (Group-2). All patients were subjected to SPECT-MPI with I.V. infusion of adenosine, and TC99-tetrofosmin. Group-1 included 69 patients (55 men, 79.7%), mean age 66.8 ± 9.8 years. Group-2 consisted of 79 patients (56 men, 70.9%), mean age 62.7 ± 11.5. There was no difference in demographics and CAD risk factors between the two groups. The SPECT-MPI revealed inferior wall ischemia, in 35 patients (50.7%), in Group-1 and 27 patients (34.1%), in Group-2 (P = 0.041). CONCLUSIONS: A relatively high rate of reversible SPECT-MPI perfusion defects may be anticipated in patients with an unobstructed NDRCA compared to patients with a dominant RCA.

Study on intraoperative localization of sentinel lymph nodes using freehand SPECT in breast cancer patients.

Introduction: The diagnostic and therapeutic approach to axillary lymph nodes is considered indispensable in the treatment of breast cancer patients. Aim: To investigate the effectiveness of 3D freehand SPECT (fhSPECT) in sentinel lymph node (SLN) mapping in breast cancer, compared with the use of a conventional gamma probe. Material and methods: We retrospectively compared the fhSPECT lymph node mapping modality, with gamma probe detection in early-stage, clinically node-negative breast cancer patients, with biopsy-confirmed malignancy. The two techniques were compared based on the average number of LNs excised per axilla. The duration of SLN mapping was also compared between the two groups. The performance of the two methods on obese and post-systemic therapy patients was evaluated. FhSPECT was used in 150 cases, while the gamma probe was employed in 50 cases. Results: FhSPECT detected at least 3 nodes in 83.3% of the patients vs. 72.0% with the γ-probe (p = 0.107). The mean number of SLNs excised per axilla was 3.66 using the γ-probe and 4.18 with fhSPECT (p = 0.03). The average surgical time was 39 ±7 min with the γ-probe and 37.54 ±17 min with fhSPECT (p = 0.228). Sentinel lymph node biopsy (SLNB) mean surgical time evolved from 40.2 ±20.77 min to 32.35 ±10.46 min (p = 0.033). In obese patients, a reduction in surgical times was noted from 45.5 ±3.09 min to 44.04 ±20.9 (p = 0.27), in addition to a significant increase in average LN detection in the fhSPECT group (4.26 ±1.44) compared to the γ-probe group (3.2 ±1.65) (p = 0.043). Conclusions: The use of the fhSPECT modality is effective and safe, and, when compared to the γ-probe, has significant advantages in SLN mapping.

Imaging myocardial inflammation of various etiologies with 99mTc-depreotide SPET/CT.

Previous reports suggested the accumulation of technetium-99m-depreotide trifluoroacetate ((99m)Tc-D) at the sites of active infection or inflammation. Binding of depreotide to over-expressed somatostatin receptors in activated lymphocytes and macrophages probably accounts for the depiction of inflammation. We speculated that myocardial inflammation could also be illustrated by (99m)Tc-D scintigraphy. We report on 3 patients with the clinical diagnosis of myocarditis of various etiologies, in which (99m)Tc-D SPET/CT demonstrated obvious tracer uptake in the myocardium of the left ventricle. In conclusion, we suggest that depreotide imaging can depict myocardial inflammation, thus supporting clinical diagnosis.

Multi-input deep learning approach for Cardiovascular Disease diagnosis using Myocardial Perfusion Imaging and clinical data.

PURPOSE: Accurate detection and treatment of Coronary Artery Disease is mainly based on invasive Coronary Angiography, which could be avoided provided that a robust, non-invasive detection methodology emerged. Despite the progress of computational systems, this remains a challenging issue. The present research investigates Machine Learning and Deep Learning methods in competing with the medical experts' diagnostic yield. Although the highly accurate detection of Coronary Artery Disease, even from the experts, is presently implausible, developing Artificial Intelligence models to compete with the human eye and expertise is the first step towards a state-of-the-art Computer-Aided Diagnostic system. METHODS: A set of 566 patient samples is analysed. The dataset contains Polar Maps derived from scintigraphic Myocardial Perfusion Imaging studies, clinical data, and Coronary Angiography results. The latter is considered as reference standard. For the classification of the medical images, the InceptionV3 Convolutional Neural Network is employed, while, for the categorical and continuous features, Neural Networks and Random Forest classifier are proposed. RESULTS: The research suggests that an optimal strategy competing with the medical expert's accuracy involves a hybrid multi-input network composed of InceptionV3 and a Random Forest. This method matches the expert's accuracy, which is 79.15% in the particular dataset. CONCLUSION: Image classification using deep learning methods can cooperate with clinical data classification methods to enhance the robustness of the predicting model, aiming to compete with the medical expert's ability to identify Coronary Artery Disease subjects, from a large scale patient dataset.

Improving the prediction of persistent and recurrent differentiated thyroid cancer using the American Thyroid Association 2015 risk stratification system.

PURPOSE: The 2015 American Thyroid Association risk stratification system (ATA RSS) is used in patients with differentiated thyroid carcinoma (DTC) to assess their risk of persistent/recurrent disease. Our aims were to validate the 2015 ATA RSS in a registry of DTC patients and to examine whether the addition of factors not included in it, such as pre-radioactive iodine therapy stimulated thyroglobulin (pre-RAI sTg), gender, and age could increase its predictive ability. METHODS: We studied 403 patients with DTC, treated at a tertiary center from 1990 to 2018 and subjected to total thyroidectomy. All patients had received RAI therapy, except those with low-risk papillary microcarcinoma. RESULTS: Of our patients, 81.9% were women and 91.1% had papillary thyroid carcinoma. After a median follow-up of 5.0 years, 53 cases of persistent and 21 cases of recurrent disease were recorded. The proportion of variance explained (PVE) regarding the outcome (presence or absence of recurrent/persistent disease) using the 2015 ATA RSS alone was 18.3% (persistence) and 16.9% (recurrence), increasing to 74.4% and 52.0%, respectively, when pre-RAI sTg was added to the logistic regression model. Gender and age were not associated with the disease outcome. In ROC analysis, pre-RAI sTg had a high predictive value for persistent (AUC 0.983, 95% CI 0.962-1.000) and recurrent disease (AUC 0.856, 95% CI 0.715-0.997). The optimal cut-offs and sensitivity, specificity, and positive and negative predictive value for pre-RAI sTg were the following: for persistence 12.75 ng/ml, 100%, 90.5%, 64%, and 100%, and for recurrence 8.05 ng/ml, 77.8%, 85.5%, 36.8%, and 97%. CONCLUSIONS: The 2015 ATA RSS displayed moderate performance in predicting recurrent/persistent disease in patients with DTC, which improved with the inclusion of pre-RAI sTg values; pre-RAI sTg was an independent predictor of the disease outcome, with high negative prognostic value.

A deep-learning-based prediction model for the biodistribution of 90 Y microspheres in liver radioembolization.

BACKGROUND: Radioembolization with 90 Y microspheres is a treatment approach for liver cancer. Currently, employed dosimetric calculations exhibit low accuracy, lacking consideration of individual patient, and tissue characteristics. PURPOSE: The purpose of the present study was to employ deep learning (DL) algorithms to differentiate patterns of pretreatment distribution of 99m Tc-macroaggregated albumin on SPECT/CT and post-treatment distribution of 90 Y microspheres on PET/CT and to accurately predict how the 90 Y-microspheres will be distributed in the liver tissue by radioembolization therapy. METHODS: Data for 19 patients with liver cancer (10 with hepatocellular carcinoma, 5 with intrahepatic cholangiocarcinoma, 4 with liver metastases) who underwent radioembolization with 90 Y microspheres were used for the DL training. We developed a 3D voxel-based variation of the Pix2Pix model, which is a special type of conditional GANs designed to perform image-to-image translation. SPECT and CT scans along with the clinical target volume for each patient were used as inputs, as were their corresponding post-treatment PET scans. The real and predicted absorbed PET doses for the tumor and the whole liver area were compared. Our model was evaluated using the leave-one-out method, and the dose calculations were measured using a tissue-specific dose voxel kernel. RESULTS: The comparison of the real and predicted PET/CT scans showed an average absorbed dose difference of 5.42% ± 19.31% and 0.44% ± 1.64% for the tumor and the liver area, respectively. The average absorbed dose differences were 7.98 ± 31.39 Gy and 0.03 ± 0.25 Gy for the tumor and the non-tumor liver parenchyma, respectively. Our model had a general tendency to underpredict the dosimetric results; the largest differences were noticed in one case, where the model underestimated the dose to the tumor area by 56.75% or 72.82 Gy. CONCLUSIONS: The proposed deep-learning-based pretreatment planning method for liver radioembolization accurately predicted 90 Y microsphere biodistribution. Its combination with a rapid and accurate 3D dosimetry method will render it clinically suitable and could improve patient-specific pretreatment planning.

Clinical Evaluation of a Three-Dimensional Internal Dosimetry Technique for Liver Radioembolization with 90Y Microspheres Using Dose Voxel Kernels.

Background: The purpose of this study was to develop a rapid, reliable, and efficient tool for three-dimensional (3D) dosimetry treatment planning and post-treatment evaluation of liver radioembolization with 90Y microspheres, using tissue-specific dose voxel kernels (DVKs) that can be used in everyday clinical practice. Materials and Methods: Two tissue-specific DVKs for 90Y were calculated through Monte Carlo (MC) simulations. DVKs for the liver and lungs were generated, and the dose distribution was compared with direct MC simulations. A method was developed to produce a 3D dose map by convolving the calculated DVKs with the activity biodistribution derived from clinical single-photon emission computed tomography (SPECT) or positron emission tomography (PET) images. Image registration for the SPECT or PET images with the corresponding computed tomography scans was performed before dosimetry calculation. The authors first compared the DVK convolution dosimetry with a direct full MC simulation on an XCAT anthropomorphic phantom. They then tested it in 25 individual clinical cases of patients who underwent 90Y therapy. All MC simulations were carried out using the GATE MC toolkit. Results: Comparison of the measured absorbed dose using tissue-specific DVKs and direct MC simulation on 25 patients revealed a mean difference of 1.07% ± 1.43% for the liver and 1.03% ± 1.21% for the tumor tissue, respectively. The largest difference between DVK convolution and full MC dosimetry was observed for the lung tissue (10.16% ± 1.20%). The DVK statistical uncertainty was <0.75% for both media. Conclusions: This semiautomatic algorithm is capable of performing rapid, accurate, and efficient 3D dosimetry. The proposed method considers tissue and activity heterogeneity using tissue-specific DVKs. Furthermore, this method provides results in <1 min, making it suitable for everyday clinical practice.

Adult Medulloblastoma Depicted With 99mTc-HYNIC-[D-Phe1, Tyr3-Octreotide] SPECT/CT.

Although medulloblastoma constitutes the second most common malignant brain tumor in children, it encountered very rarely in adults. The incidence of adult medulloblastoma is approximately 0.6 to 1 case per million. It accounts for less than 1% of adult brain tumors and is located most commonly at the posterior cranial fossa. We present an extremely rare case of a 67-year-old man with cerebellar medulloblastoma with residual disease after surgery, chemotherapy, and radiation therapy, depicted with Tc-HYNIC-[D-Phe, Tyr-Octreotide] SPECT/CT. Somatostatin receptor scintigraphy was performed for staging and for the possibility of treatment with somatostatin analogs or peptide radionuclide therapy.