Radiomics-enhanced early regression index for predicting treatment response in rectal cancer: a multi-institutional 0.35 T MRI-guided radiotherapy study.

PURPOSE: The accurate prediction of treatment response in locally advanced rectal cancer (LARC) patients undergoing MRI-guided radiotherapy (MRIgRT) is essential for optimising treatment strategies. This multi-institutional study aimed to investigate the potential of radiomics in enhancing the predictive power of a known radiobiological parameter (Early Regression Index, ERITCP) to evaluate treatment response in LARC patients treated with MRIgRT. METHODS: Patients from three international sites were included and divided into training and validation sets. 0.35 T T2*/T1-weighted MR images were acquired during simulation and at each treatment fraction. The biologically effective dose (BED) conversion was used to account for different radiotherapy schemes: gross tumour volume was delineated on the MR images corresponding to specific BED levels and radiomic features were then extracted. Multiple logistic regression models were calculated, combining ERITCP with other radiomic features. The predictive performance of the different models was evaluated on both training and validation sets by calculating the receiver operating characteristic (ROC) curves. RESULTS: A total of 91 patients was enrolled: 58 were used as training, 33 as validation. Overall, pCR was observed in 25 cases. The model showing the highest performance was obtained combining ERITCP at BED = 26 Gy with a radiomic feature (10th percentile of grey level histogram, 10GLH) calculated at BED = 40 Gy. The area under ROC curve (AUC) of this combined model was 0.98 for training set and 0.92 for validation set, significantly higher (p = 0.04) than the AUC value obtained using ERITCP alone (0.94 in training and 0.89 in validation set). CONCLUSION: The integration of the radiomic analysis with ERITCP improves the pCR prediction in LARC patients, offering more precise predictive models to further personalise 0.35 T MRIgRT treatments of LARC patients.

Dapagliflozin treatment is associated with a reduction of epicardial adipose tissue thickness and epicardial glucose uptake in human type 2 diabetes.

OBJECTIVE: We recently demonstrated that treatment with sodium-glucose cotransporter-2 inhibitors (SGLT-2i) leads to an increase in myocardial flow reserve in patients with type 2 diabetes (T2D) with stable coronary artery disease (CAD). The mechanism by which this occurs is, however, unclear. One of the risk factors for cardiovascular disease is inflammation of epicardial adipose tissue (EAT). Since the latter is often increased in type 2 diabetes patients, it could play a role in coronary microvascular dysfunction. It is also well known that SGLT-2i modify adipose tissue metabolism. We aimed to investigate the effects of the SGLT-2i dapagliflozin on metabolism and visceral and subcutaneous adipose tissue thickness in T2D patients with stable coronary artery disease and to verify whether these changes could explain observed changes in myocardial flow. METHODS: We performed a single-center, prospective, randomized, double-blind, controlled clinical trial with 14 T2D patients randomized 1:1 to SGLT-2i dapagliflozin (10 mg daily) or placebo. The thickness of visceral (epicardial, mediastinal, perirenal) and subcutaneous adipose tissue and glucose uptake were assessed at baseline and 4 weeks after treatment initiation by 2-deoxy-2-[18F]fluoro-D-glucose Positron Emission Tomography/Computed Tomography during hyperinsulinemic euglycemic clamp. RESULTS: The two groups were well-matched for baseline characteristics (age, diabetes duration, HbA1c, BMI, renal and heart function). Dapagliflozin treatment significantly reduced EAT thickness by 19% (p = 0.03). There was a significant 21.6% reduction in EAT glucose uptake during euglycemic hyperinsulinemic clamp in the dapagliflozin group compared with the placebo group (p = 0.014). There were no significant effects on adipose tissue thickness/metabolism in the other depots explored. CONCLUSIONS: SGLT-2 inhibition selectively reduces EAT thickness and EAT glucose uptake in T2D patients, suggesting a reduction of EAT inflammation. This could explain the observed increase in myocardial flow reserve, providing new insights into SGLT-2i cardiovascular benefits.

Magnetic resonance-guided stereotactic body radiation therapy (MRgSBRT) for oligometastatic patients: a single-center experience.

PURPOSE: Stereotactic body radiotherapy is increasingly used for the treatment of oligometastatic disease. Magnetic resonance-guided stereotactic radiotherapy (MRgSBRT) offers the opportunity to perform dose escalation protocols while reducing the unnecessary irradiation of the surrounding organs at risk. The aim of this retrospective, monoinstitutional study is to evaluate the feasibility and clinical benefit (CB) of MRgSBRT in the setting of oligometastatic patients. MATERIALS AND METHODS: Data from oligometastatic patients treated with MRgSBRT were collected. The primary objectives were to define the 12-month progression-free survival (PFS) and local progression-free survival (LPFS) and 24-month overall survival (OS) rate. The objective response rate (ORR) included complete response (CR) and partial response (PR). CB was defined as the achievement of ORR and stable disease (SD). Toxicities were also assessed according to the CTCAE version 5.0 scale. RESULTS: From February 2017 to March 2021, 59 consecutive patients with a total of 80 lesions were treated by MRgSBRT on a 0.35 T hybrid unit. CR and PR as well as SD were observed in 30 (37.5%), 7 (8.75%), and 17 (21.25%) lesions, respectively. Furthermore, CB was evaluated at a rate of 67.5% with an ORR of 46.25%. Median follow-up time was 14 months (range: 3-46 months). The 12-month LPFS and PFS rates were 70% and 23%, while 24-month OS rate was 93%. No acute toxicity was reported, whereas late pulmonary fibrosis G1 was observed in 9 patients (15.25%). CONCLUSION: MRgSBRT was well tolerated by patients with reported low toxicity levels and a satisfying CB.

Use of secondary air kerma from dose area product and fluoroscopy time for preventive effective dose estimation in interventional radiology procedures for staff.

INTRODUCTION: interventional radiology workers are potentially exposed to high levels of ionizing radiation, therefore preventive dose estimation is mandatory for the correct risk classification of staff. Effective dose (ED) is a radiation protection quantity strictly related to the secondary air kerma (KS), using appropriate multiplicative conversion factors (ICRP 106). The aim of this work is to evaluate the accuracy ofKSestimated from physically measurable quantities such as dose-area product (DAP) or fluoroscopy time (FT). METHODS: radiological units (n= 4) were characterized in terms of primary beam air kerma and DAP-meter response, consequently defining a DAP-meter correction factor (CF) for each unit.KS, scattered from an anthropomorphic phantom and measured by a digital multimeter, was then compared with the value estimated from DAP and FT. Different combinations of tube voltages, field sizes, current and scattering angles were used to simulate the variation of working conditions. Further measurements were performed to estimate the couch transmission factor for different phantom placements on the operational couch, defining a CF as the mean transmission factor. RESULTS: when no CFs were applied, the measuredKSshowed a median percentage difference of between 33.8% and 115.7% with respect toKSevaluated from DAP, and between -46.3% and 101.8% forKSevaluated from FT. By contrast, when previously defined CFs were applied to the evaluatedKS, the median percentage difference between the measuredKSand the value evaluated from DAP ranged from between -7.94% and 15.0%, and between -66.2% and 17.2% for that evaluated from FT. CONCLUSION: when appropriate CF are applied, the preventive ED estimation from the median DAP value seems to be more conservative and easier to obtain with respect to the one obtained from the FT value. Further measurements should be performed with a personal dosimeter during routine activities to assess the properKSto ED conversion factor.

Dapagliflozin improves myocardial flow reserve in patients with type 2 diabetes: the DAPAHEART Trial: a preliminary report.

OBJECTIVE: Cardiovascular (CV) outcome trials have shown that in patients with type 2 diabetes (T2D), treatment with sodium-glucose cotransporter-2 inhibitors (SGLT-2i) reduces CV mortality and hospital admission rates for heart failure (HF). However, the mechanisms behind these benefits are not fully understood. This study was performed to investigate the effects of the SGLT-2i dapagliflozin on myocardial perfusion and glucose metabolism in patients with T2D and stable coronary artery disease (coronary stenosis ≥ 30% and < 80%), with or without previous percutaneous coronary intervention (> 6 months) but no HF. METHODS: This was a single-center, prospective, randomized, double-blind, controlled clinical trial including 16 patients with T2D randomized to SGLT-2i dapagliflozin (10 mg daily) or placebo. The primary outcome was to detect changes in myocardial glucose uptake (MGU) from baseline to 4 weeks after treatment initiation by [(18)F]2-deoxy-2-fluoro-D-glucose (FDG) PET/CT during hyperinsulinemic euglycemic clamp. The main secondary outcome was to assess whether the hypothetical changes in MGU were associated with changes in myocardial blood flow (MBF) and myocardial flow reserve (MFR) measured by 13N-ammonia PET/CT. The study was registered at eudract.ema.europa.eu (EudraCT No. 2016-003614-27) and ClinicalTrials.gov (NCT03313752). RESULTS: 16 patients were randomized to dapagliflozin (n = 8) or placebo (n = 8). The groups were well-matched for baseline characteristics (age, diabetes duration, HbA1c, renal and heart function). There was no significant change in MGU during euglycemic hyperinsulinemic clamp in the dapagliflozin group (2.22 ± 0.59 vs 1.92 ± 0.42 µmol/100 g/min, p = 0.41) compared with the placebo group (2.00 ± 0.55 vs 1.60 ± 0.45 µmol/100 g/min, p = 0.5). Dapagliflozin significantly improved MFR (2.56 ± 0.26 vs 3.59 ± 0.35 p = 0.006 compared with the placebo group 2.34 ± 0.21 vs 2.38 ± 0.24 p = 0.81; pint = 0.001) associated with a reduction in resting MBF corrected for cardiac workload (p = 0.005; pint = 0.045). A trend toward an increase in stress MBF was also detected (p = 0.054). CONCLUSIONS: SGLT-2 inhibition increases MFR in T2D patients. We provide new insight into SGLT-2i CV benefits, as our data show that patients on SGLT-2i are more resistant to the detrimental effects of obstructive coronary atherosclerosis due to increased MFR, probably caused by an improvement in coronary microvascular dysfunction. Trial registration EudraCT No. 2016-003614-27; ClinicalTrials.gov Identifier: NCT03313752.

Automated hybrid volumetric modulated arc therapy (HVMAT) for whole-breast irradiation with simultaneous integrated boost to lumpectomy area : A treatment planning study.

PURPOSE: To develop an automated treatment planning approach for whole breast irradiation with simultaneous integrated boost using an automated hybrid VMAT class solution (HVMAT). MATERIALS AND METHODS: Twenty-five consecutive patients with left breast cancer received 50 Gy (2 Gy/fraction) to the whole breast and an additional simultaneous 10 Gy (2.4 Gy/fraction) to the tumor cavity. Ipsilateral lung, heart, and contralateral breast were contoured as main organs-at-risk. HVMAT plans were inversely optimized by combining two open fields with a VMAT semi-arc beam. Open fields were setup to include the whole breast with a 2 cm flash region and to carry 80% of beams weight. HVMAT plans were compared with three tangential techniques: conventional wedged-field tangential plans (SWF), field-in-field forward planned tangential plans (FiF), and hybrid-IMRT plans (HMRT). Dosimetric differences among the plans were evaluated using Kruskal-Wallis one-way analysis of variance. Dose accuracy was validated using the PTW Octavius-4D phantom together with the 1500 2D-array. RESULTS: No significant differences were found among the four techniques for both targets coverage. HVMAT plans showed consistently better PTVs dose contrast, conformity, and homogeneity (p < 0.001 for all metrics) and statistically significant reduction of high-dose breast irradiation. V55 and V60 decreased by 30.4, 26.1, and 20.8% (p < 0.05) and 12.3, 9.9, and 6.0% (p < 0.05) for SWF, FIF, and HMRT, respectively. Pretreatment dose verification reported a gamma pass-rate greater than the acceptance threshold of 95% for all HVMAT plans. In addition, HVMAT reduced the time for full planning optimization to about 20 min. CONCLUSIONS: HVMAT plans resulted in superior target dose conformity and homogeneity compared to other tangential techniques. Due to fast planning time HVMAT can be applied for all patients, minimizing the impact on human or departmental resources.

CT angiography-based radiomics as a tool for carotid plaque characterization: a pilot study.

PURPOSES: Radiomics is a quantitative method able to analyze a high-throughput extraction of minable imaging features. Herein, we aim to develop a CT angiography-based radiomics analysis and machine learning model for carotid plaques to discriminate vulnerable from no vulnerable plaques. MATERIALS AND METHODS: Thirty consecutive patients with carotid atherosclerosis were enrolled in this pilot study. At surgery, a binary classification of plaques was adopted ("hard" vs "soft"). Feature extraction was performed using the R software package Moddicom. Pairwise feature interdependencies were evaluated using the Spearman rank correlation coefficient. A univariate analysis was performed to assess the association between each feature and the plaque classification and chose top-ranked features. The feature predictive value was investigated using binary logistic regression. A stepwise backward elimination procedure was performed to minimize the Akaike information criterion (AIC). The final significant features were used to build the models for binary classification of carotid plaques, including logistic regression (LR), support vector machine (SVM), and classification and regression tree analysis (CART). All models were cross-validated using fivefold cross validation. Class-specific accuracy, precision, recall and F-measure evaluation metrics were used to quantify classifier output quality. RESULTS: A total of 230 radiomics features were extracted from each plaque. Pairwise Spearman correlation between features reported a high level of correlations, with more than 80% correlating with at least one other feature at |ρ|> 0.8. After a stepwise backward elimination procedure, the entropy and volume features were found to be the most significantly associated with the two plaque groups (p < 0.001), with AUCs of 0.92 and 0.96, respectively. The best performance was registered by the SVM classifier with the RBF kernel, with accuracy, precision, recall and F-score equal to 86.7, 92.9, 81.3 and 86.7%, respectively. The CART classification tree model for the entropy and volume features model achieved 86.7% well-classified plaques and an AUC of 0.987. CONCLUSION: This pilot study highlighted the potential of CTA-based radiomics and machine learning to discriminate plaque composition. This new approach has the potential to provide a reliable method to improve risk stratification in patients with carotid atherosclerosis.

Quantitative analysis of MRI-guided radiotherapy treatment process time for tumor real-time gating efficiency.

PURPOSE: Magnetic Resonance-guided radiotherapy (MRgRT) systems allow continuous monitoring of therapy volumes during treatment delivery and personalized respiratory gating approaches. Treatment length may therefore be significantly affected by patient's compliance and breathing control. We quantitatively analyzed treatment process time efficiency (TE ) using data obtained from real-world patient treatment logs to optimize MRgRT delivery settings. METHODS: Data corresponding to the first 100 patients treated with a low T hybrid MRI-Linac system, both in free breathing (FB) and in breath hold inspiration (BHI) were collected. TE has been computed as the percentage difference of the actual single fraction's total treatment time and the predicted treatment process time, as computed by the TPS during plan optimization. Differences between the scheduled and actual treatment room occupancy time were also evaluated. Finally, possible correlations with planning, delivery and clinical parameters with TE were also investigated. RESULTS: Nine hundred and nineteen treatment fractions were evaluated. TE difference between BHI and FB patients' groups was statistically significant and the mean TE were 42.4%, and -0.5% respectively. No correlation was found with TE for BHI and FB groups. Planning, delivering and clinical parameters classified BHI and FB groups, but no correlation with TE was found. CONCLUSION: The use of BHI gating technique can increase the treatment process time significantly. BHI technique could be not always an adequate delivery technique to optimize the treatment process time. Further gating techniques should be considered to improve the use of MRgRT.

Radiation dose in nuclear medicine: the hybrid imaging.

Hybrid imaging procedures such as single-photon emission computed tomography/computed tomography (SPECT/CT) and positron emission tomography/computed tomography (PET/CT) showed a rapid diffusion in recent years because of their high sensitivity, specificity, and accuracy, due to a more accurate localization and definition of scintigraphic findings. However, hybrid systems inevitably lead to an increase in patient radiation exposure because of the added CT component. Effective doses due to the radiopharmaceuticals can be estimated by multiplying the administered activities by the effective dose coefficients, while for the CT component the dose-length product can be multiplied by a conversion coefficient k. However, the effective dose value is subject to a high degree of uncertainty and must be interpreted as a broad, generic estimate of biologic risk. Although the effective dose can be used to estimate and compare the risk of radiation exposure across multiple imaging techniques, clinicians should be aware that it represents a generic evaluation of the risk derived from a given procedure to a generic model of the human body. It cannot be applied to a single individual and should not be used for epidemiologic studies or the estimation of population risks due to the inherent uncertainties and oversimplifications involved. Practical ways to reduce radiation dose to patients eligible for hybrid imaging involve adjustments to both the planning phase and throughout the execution of the study. These methods include individual justification of radiation exposure, radiopharmaceutical choice, adherence to diagnostic reference levels (DLR), patient hydration and bladder voiding, adoption of new technical devices (sensitive detectors or collimators) with new reconstruction algorithms, and implementation of appropriate CT protocols and exposure parameters.

Are the simplified methods to estimate Ki in 18F-FDG PET studies feasible in clinical routine? Comparison between three simplified methods.

BACKGROUND: The aim of this study was to verify the feasibility, in clinical practice, of three simplified methods (Hunter, Sadato and another one proposed by our group) to calculate Ki and MRglu of 18F-FDG, comparing the results with those derived by the linear regression (LR) method (considered the golden standard), and also with SUV. METHODS: Forty-five patients (32males, mean age 69±9years) with non-small-cell-lung cancer prospectively enrolled, underwent dynamic 18F-FDG PET-CT over the thorax. Ki was estimated as follows: from a static acquisition and performing one venous blood sampling using the Hunter method; multiplying the SUV for the average plasma clearance rate (kP(T)) and for the initial distribution volume (V0bw) without performing any blood sampling using the Sadato method; multiplying the SUV for a factor F (which encompasses the mean value of haematocrit and plasma volume, both according to patient's sex) without performing any blood sample using ours method. Wilcoxon signed rank and coefficient of determination (R2) were used for statistical analysis. RESULTS: No significant difference was observed between the Ki and MRglu estimated by all three simplified methods and the Ki and MRglu estimated by LR. The highest P values and the lower values of mean differences were observed with our method compared with LR: Ki=0.0392±0.0178 min-1 vs. Ki=0.0392±0.0202 min-1 (P=0.897, MD=0.0001 min-1), respectively; MRglu= 4.47±2.23 ml/min/100g vs. MRglu= 4.43±2.38 ml/min/100g (P=0.839, MD= -0.0373 mL/min/100g), respectively. The highest correlation was observed between the Ki estimated by both Hunter and our methods and the Ki estimated by LR: R2=0.87, R2=0.86, respectively. A good correlation (R2=0.83) was observed between SUV and Ki estimated by LR. CONCLUSIONS: These three simplified methods represent a valid alternative to the more invasive and complex full kinetic analysis. Their "pros" are: the non-invasiveness, the feasibility, the good correlation with the golden standard; their "cons" is that full kinetic analysis provides highest accuracy in Ki determination. Therefore, in clinical oncology routine, the nuclear physicians can choose among different simplified methods especially for monitoring the response to treatment, for tumour grading, and for prognostic stratification, letting the full kinetic analysis to specific centre/studies.

Comparative analysis of iterative reconstruction algorithms with resolution recovery and time of flight modeling for 18F-FDG cardiac PET: A multi-center phantom study.

BACKGROUND: The purpose of this study was to evaluate the image quality in cardiac 18F-FDG PET using the time of flight (TOF) and/or point spread function (PSF) modeling in the iterative reconstruction (IR). METHODS: Three scanners and an anthropomorphic cardiac phantom with an insert simulating a transmural defect (TD) were used. Two sets of scans (with/without TD) were acquired, and four reconstruction schemes were considered: (1) IR; (2) IR + PSF, (3) IR + TOF, and (4) IR + TOF + PSF. LV wall thickness (FWHM), contrast between LV wall and inner chamber (C IC), and TD contrast in LV wall (C TD) were evaluated. RESULTS: Tests of the reconstruction protocols showed a decrease in FWHM from IR (13 mm) to IR + PSF (11 mm); an increase in the C IC from IR (65%) to IR + PSF (71%) and from IR + TOF (72%) to IR + TOF + PSF (77%); and an increase in the C TD from IR + PSF (72%) to IR + TOF (75%) and to IR + TOF + PSF (77%). Tests of the scanner/software combinations showed a decrease in FWHM from Gemini_TF (13 mm) to Biograph_mCT (12 mm) and to Discovery_690 (11 mm); an increase in the C IC from Gemini_TF (65%) to Biograph_mCT (73%) and to Discovery_690 (75%); and an increase in the C TD from Gemini_TF/Biograph_mCT (72%) to Discovery_690 (77%). CONCLUSION: The introduction of TOF and PSF increases image quality in cardiac 18F-FDG PET. The scanner/software combinations exhibit different performances, which should be taken into consideration when making cross comparisons.

Comparative analysis of cadmium-zincum-telluride cameras dedicated to myocardial perfusion SPECT: A phantom study.

BACKGROUND: This investigation used image data generated by an anthropomorphic phantom with a cardiac insert for a comparison between two solid state cameras: D-SPECT and D530c. METHODS: For each camera, two sets (with and without a simulated transmural defect (TD)) of scans were acquired starting from the in vivo standard count statistics in the left ventricle (LV). Other two acquisitions corresponding to 150% and 50% of the reference count statistics were acquired. Five performance indices related to spatial resolution, contrast, and contrast-to-noise ratio (CNR) were analyzed. RESULTS: D-SPECT showed a lower LV wall thickness and an inferior sharpness than D530c. No significant differences were found in terms of contrast between LV wall and the inner cavity, TD contrast or CNR. No significant differences were observed in CNR when moving from the reference level of count statistics down to 50% or up to 150% of the counts acquired on the LV. CONCLUSIONS: Our results show that D-SPECT and D530c have different performances. The lack of differences in the image performance indices along the range of count statistics explored, indicates that there is the possibility for a further reduction in the injected activity and/or the acquisition time, for both systems.

The contest between internal and external-beam dosimetry: The Zeno's paradox of Achilles and the tortoise.

Radionuclide therapy, also called molecular radiotherapy (MRT), has come of age, with several novel radiopharmaceuticals being approved for clinical use or under development in the last decade. External beam radiotherapy (EBRT) is a well-established treatment modality, with about half of all oncologic patients expected to receive at least one external radiation treatment over their disease course. The efficacy and the toxicity of both types of treatment rely on the interaction of radiation with biological tissues. Dosimetry played a fundamental role in the scientific and technological evolution of EBRT, and absorbed doses to the target and to the organs at risk are calculated on a routine basis. In contrast, in MRT the usefulness of internal dosimetry has long been questioned, and a structured path to include absorbed dose calculation is missing. However, following a similar route of development as EBRT, MRT treatments could probably be optimized in a significant proportion of patients, likely based on dosimetry and radiobiology. In the present paper we describe the differences and the similarities between internal and external-beam dosimetry in the context of radiation treatments, and we retrace the main stages of their development over the last decades.

Impact of bias field correction on 0.35 T pelvic MR images: evaluation on generative adversarial network-based OARs' auto-segmentation and visual grading assessment.

Purpose: Magnetic resonance imaging (MRI)-guided radiotherapy enables adaptive treatment plans based on daily anatomical changes and accurate organ visualization. However, the bias field artifact can compromise image quality, affecting diagnostic accuracy and quantitative analyses. This study aims to assess the impact of bias field correction on 0.35 T pelvis MRIs by evaluating clinical anatomy visualization and generative adversarial network (GAN) auto-segmentation performance. Materials and methods: 3D simulation MRIs from 60 prostate cancer patients treated on MR-Linac (0.35 T) were collected and preprocessed with the N4ITK algorithm for bias field correction. A 3D GAN architecture was trained, validated, and tested on 40, 10, and 10 patients, respectively, to auto-segment the organs at risk (OARs) rectum and bladder. The GAN was trained and evaluated either with the original or the bias-corrected MRIs. The Dice similarity coefficient (DSC) and 95th percentile Hausdorff distance (HD95th) were computed for the segmented volumes of each patient. The Wilcoxon signed-rank test assessed the statistical difference of the metrics within OARs, both with and without bias field correction. Five radiation oncologists blindly scored 22 randomly chosen patients in terms of overall image quality and visibility of boundaries (prostate, rectum, bladder, seminal vesicles) of the original and bias-corrected MRIs. Bennett's S score and Fleiss' kappa were used to assess the pairwise interrater agreement and the interrater agreement among all the observers, respectively. Results: In the test set, the GAN trained and evaluated on original and bias-corrected MRIs showed DSC/HD95th of 0.92/5.63 mm and 0.92/5.91 mm for the bladder and 0.84/10.61 mm and 0.83/9.71 mm for the rectum. No statistical differences in the distribution of the evaluation metrics were found neither for the bladder (DSC: p = 0.07; HD95th: p = 0.35) nor for the rectum (DSC: p = 0.32; HD95th: p = 0.63). From the clinical visual grading assessment, the bias-corrected MRI resulted mostly in either no change or an improvement of the image quality and visualization of the organs' boundaries compared with the original MRI. Conclusion: The bias field correction did not improve the anatomy visualization from a clinical point of view and the OARs' auto-segmentation outputs generated by the GAN.

Impact of data transfer between treatment planning systems on dosimetric parameters.

PURPOSE: In radiotherapy it is often necessary to transfer a patient's DICOM (Digital Imaging and COmmunications in Medicine) dataset from one system to another for re-treatment, plan-summation or registration purposes. The aim of the study is to evaluate effects of dataset transfer between treatment planning systems. MATERIALS AND METHODS: Twenty-five patients treated in a 0.35T MR-Linac (MRidian, ViewRay) for locally-advanced pancreatic cancer were enrolled. For each patient, a nominal dose distribution was optimized on the planning MRI. Each plan was daily re-optimized if needed to match the anatomy and exported from MRIdian-TPS (ViewRay Inc.) to Eclipse-TPS (Siemens-Varian). A comparison between the two TPSs was performed considering the PTV and OARs volumes (cc), as well as dose coverages and clinical constraints. RESULTS: From the twenty-five enrolled patients, 139 plans were included in the data comparison. The median values of percentage PTV volume variation are 10.8 % for each fraction, while percentage differences of PTV coverage have a mean value of -1.4 %. The median values of the percentage OARs volume variation are 16.0 %, 7.0 %, 10.4 % and 8.5 % for duodenum, stomach, small and large bowel, respectively. The percentage variations of the dose constraints are 41.0 %, 52.7 % and 49.8 % for duodenum, stomach and small bowel, respectively. CONCLUSIONS: This study has demonstrated a non-negligible variation in size and dosimetric parameters when datasets are transferred between TPSs. Such variations should be clinically considered. Investigations are focused on DICOM structure algorithm employed by the TPSs during the transfer to understand the cause of such variations.

Auto-segmentation of pelvic organs at risk on 0.35T MRI using 2D and 3D Generative Adversarial Network models.

PURPOSE: Manual recontouring of targets and Organs At Risk (OARs) is a time-consuming and operator-dependent task. We explored the potential of Generative Adversarial Networks (GAN) to auto-segment the rectum, bladder and femoral heads on 0.35T MRIs to accelerate the online MRI-guided-Radiotherapy (MRIgRT) workflow. METHODS: 3D planning MRIs from 60 prostate cancer patients treated with 0.35T MR-Linac were collected. A 3D GAN architecture and its equivalent 2D version were trained, validated and tested on 40, 10 and 10 patients respectively. The volumetric Dice Similarity Coefficient (DSC) and 95th percentile Hausdorff Distance (HD95th) were computed against expert drawn ground-truth delineations. The networks were also validated on an independent external dataset of 16 patients. RESULTS: In the internal test set, the 3D and 2D GANs showed DSC/HD95th of 0.83/9.72 mm and 0.81/10.65 mm for the rectum, 0.92/5.91 mm and 0.85/15.72 mm for the bladder, and 0.94/3.62 mm and 0.90/9.49 mm for the femoral heads. In the external test set, the performance was 0.74/31.13 mm and 0.72/25.07 mm for the rectum, 0.92/9.46 mm and 0.88/11.28 mm for the bladder, and 0.89/7.00 mm and 0.88/10.06 mm for the femoral heads. The 3D and 2D GANs required on average 1.44 s and 6.59 s respectively to generate the OARs' volumetric segmentation for a single patient. CONCLUSIONS: The proposed 3D GAN auto-segments pelvic OARs with high accuracy on 0.35T, in both the internal and the external test sets, outperforming its 2D equivalent in both segmentation robustness and volume generation time.

A prospective analysis of ¹8F-FDG PET/CT in patients with uveal melanoma: comparison between metabolic rate of glucose (MRglu) and standardized uptake value (SUV) and correlations with histopathological features.

PURPOSE: To evaluate whether standardized uptake value (SUV) and/or metabolic rate of glucose (MRglu) are different among epithelioid, mixed, and spindle cell uveal melanomas, as well as between low and high risk melanomas; to correlate ultrasonographic data and metabolic parameters with histopathological features; and to assess the role of (18)F-FDG PET/CT for evaluating prognosis. METHODS: Of 34 eligible patients prospectively enrolled with clinical suspicion of medium/large uveal melanoma, 26 (15 men, mean age 62.8 ± 11.8 years) were evaluated. All patients underwent metastatic work-up, 3-D dynamic brain and whole-body (18)F-FDG PET/CT, and surgery. RESULTS: Of the 26 ocular lesions, 23 showed (18)F-FDG uptake, with a sensitivity of 88 %. MRglu was significantly higher in the epithelioid cell melanomas than in the spindle cell melanomas, as well as in high-risk lesions than in low-risk lesions (p = 0.01, p = 0.02, respectively). SUV and MRglu were correlated with histopathological features while ultrasonographic data were not. CONCLUSION: MRglu is useful for distinguishing the different cell types in uveal melanoma, as well as high-risk from low-risk lesions, while SUV is not. MRglu provides a more accurate evaluation of glucose consumption, whereas SUV provides only an estimation. In addition, the metabolic parameters correlate with histopathological features, well also reflecting cellular behaviour in ocular malignancy. A longer follow-up is needed to assess the role of (18)F-FDG in evaluating prognosis.

Synchronous Treatment of Breast Cancer Hepatic Metastases by Transarterial Radioembolization and Radiofrequency Thermoablation: A Case Report.

ABSTRACT: In a 51-year-old woman affected by breast cancer, hepatic recurrence of disease was managed by concurrent 90 Y-labeled glass microsphere embolization (transarterial radioembolization) and radiofrequency thermoablation. Intention-to-treat target, candidate to radioembolization, was in the IV hepatic segment; another lesion, managed with radiofrequency thermoablation, was in the VI-VII hepatic segment. Concomitant correction of a duodenocephalopancreatic shunting was performed as well. Thermoablation did not interfere with distribution of 99m Tc-macroaggregated albumin and 90 Y-labeled microspheres to the target and healthy liver. At our knowledge, this is the first report that combines 2 locoregional procedures in different hepatic segments on the same day.

The Importance of Uncertainty Analysis and Traceable Measurements in Routine Quantitative 90Y-PET Molecular Radiotherapy: A Multicenter Experience.

Molecular Radiation Therapy (MRT) is a valid therapeutic option for a wide range of malignancies, such as neuroendocrine tumors and liver cancers. In its practice, it is generally acknowledged that there is a need to evaluate the influence of different factors affecting the accuracy of dose estimates and to define the actions necessary to maintain treatment uncertainties at acceptable levels. The present study addresses the problem of uncertainty propagation in 90Y-PET quantification. We assessed the quantitative accuracy in reference conditions of three PET scanners (namely, Siemens Biograph mCT, Siemens Biograph mCT flow, and GE Discovery DST) available at three different Italian Nuclear Medicine centers. Specific aspects of uncertainty within the quantification chain have been addressed, including the uncertainty in the calibration procedure. A framework based on the Guide to the Expression of Uncertainty in Measurement (GUM) approach is proposed for modeling the uncertainty in the quantification processes, and ultimately, an estimation of the uncertainty achievable in clinical conditions is reported.

Mesorectal motion evaluation in rectal cancer MR-guided radiotherapy: an exploratory study to quantify treatment margins.

BACKGROUND: Mesorectal motion (MM) is a source of uncertainty during neoadjuvant chemoradiotherapy (nCRT) delivery for locally advanced rectal cancer (LARC). Previously published experiences using cone-beam computed tomography imaging have already described significant movement. Aim of this analysis is to assess inter-fraction MM using the higher tissue contrast provided by hybrid magnetic resonance imaging (MRI) in LARC patients (pts) treated with MRI guided radiation therapy (MRgRT). METHODS: The total mesorectum, its superior (Msup), middle (Mmid) and lower (Mlow) regions were contoured on the positioning MRIs acquired on simulation day and on each treatment day. Six PTVs were obtained adding 0.5, 0.7, 1, 1.3, 1.5 and 2 cm margin to the whole mesorectum, starting from the simulation MRI. Margins including 95% of the mesorectal structures during whole treatment in 95% of patients (pts) were considered adequate. RESULTS: A total number of 312 fractions of 12 consecutive pts was retrospectively analyzed. The different mesorectum regions show specific motion variability. In particular, Msup shows larger variability in left, right and anterior directions, while the Mlow in caudal and posterior ones. The anterior margin is significantly larger in the Msup than in the other regions. CONCLUSION: Different mesorectal regions move differently throughout the radiotherapy treatment, with the largest MM in the Msup anterior direction. Asymmetrical margins are recommended.