Correction for FDG PET dose extravasations: Monte Carlo validation and quantitative evaluation of patient studies

Radiopharmaceutical administration practices-Are they best practice?

Background

The nuclear medicine community has stated that they are using best practices to gain venous access and administer radiopharmaceuticals, and therefore do not contribute to extravasations. We tested this hypothesis qualitatively and quantitatively by evaluating four different perspectives of current radiopharmaceutical administration practices: (1) clinical observations of nuclear medicine technologists on the job, (2) quality improvement (QI) projects, (3) a high-level survey of current practices in 10 acute care hospitals, (4) intravenous (IV) access site data for 29,343 procedures. These four areas were compared to the gold standard of pharmaceutical administration techniques.

Results

From clinical observations of radiopharmaceutical administrations in adult populations, technologists extensively used 24-gauge peripheral intravenous catheters (PIVCs) and butterfly needles. They also performed direct puncture (straight stick). Technologists predominantly chose veins in areas of flexion (hand, wrist, and antecubital fossa), rather than forearm vessels for IV access placement; in many circumstances, antecubital fossa vessels are chosen first, often without prior assessment for other suitable vessels. For selecting the injection vein, technologists sometimes used infrared vein finders but primarily performed blind sticks. Review of QI projects suggested that smaller gauge needles were contributing factors to extravasations. Additionally, the review of surveys from 10 hospitals revealed an absence of formalized protocols, training, knowledge, and skills necessary to ensure the safety/patency of IV devices prior to the administration of radiopharmaceuticals. Finally, findings from a review of IV access data for 29,343 procedures supported the observations described above.

Conclusions

We expect that nuclear medicine technologists have the best intentions when providing patient care, but many do not follow venous access best practices; they lack formal protocols, have not received the latest comprehensive training, and do not use the best placement tools and monitoring equipment. Thus, the presumption that most nuclear medicine technologists use best practices may not be accurate. In order to improve radiopharmaceutical administration and patient care, the nuclear medicine community should update technical standards to address the most recent peripheral IV access and administration best practices, provide technologists with vascular visualization tools and the proper training, develop and require annual vascular access competency, and provide active monitoring with center and patient-specific data to create ongoing feedback.

Safety injections of nuclear medicine radiotracers: towards a new modality for a real-time detection of extravasation events and 18F-FDG SUV data correction

BACKGROUND

¹⁸F-FDG PET/CT imaging allows to study oncological patients and their relative diagnosis through the standardised uptake value (SUV) evaluation. During radiopharmaceutical injection, an extravasation event may occur, making the SUV value less accurate and possibly leading to severe tissue damage. The study aimed to propose a new technique to monitor and manage these events, to provide an early evaluation and correction to the estimated SUV value through a SUV correction coefficient.

METHODS

A cohort of 70 patients undergoing ¹⁸F- FDG PET/CT examinations was enrolled. Two portable detectors were secured on the patients' arms. The dose-rate (DR) time curves on the injected DRⁱⁿ and contralateral DR^con arm were acquired during the first 10 min of injection. Such data were processed to calculate the parameters Δpⁱⁿ_NOR = (DRⁱⁿ_max- DRⁱⁿ_mean)/DRⁱⁿ_max and ΔR_t = (DRⁱⁿ(t) - DR^con(t)), where DRⁱⁿ_max is the maximum DR value, DRⁱⁿ_mean is the average DR value in the injected arm. OLINDA software allowed dosimetric estimation of the dose in the extravasation region. The estimated residual activity in the extravasation site allowed the evaluation of the SUV's correction value and to define an SUV correction coefficient.

RESULTS

Four cases of extravasations were identified for which ΔR_t [(390 ± 26) µSv/h], while ΔR_t [(150 ± 22) µSv/h] for abnormal and ΔR_t [(24 ± 11) µSv/h] for normal cases. The Δpⁱⁿ_NOR showed an average value of (0.44 ± 0.05) for extravasation cases and an average value of (0.91 ± 0.06) and (0.77 ± 0.23) in normal and abnormal classes, respectively. The percentage of SUV reduction (SUV_%CR) ranges between 0.3% and 6%. The calculated self-tissue dose values range from 0.027 to 0.573 Gy, according to the segmentation modality. A similar correlation between the inverse of Δpⁱⁿ_NOR and the normalised ΔR_t with the SUV correction coefficient was found.

CONCLUSIONS

The proposed metrics allowed to characterised the extravasation events in the first few minutes after the injection, providing an early SUV correction when necessary. We also assume that the characterisation of the DR-time curve of the injection arm is sufficient for the detection of extravasation events. Further validation of these hypotheses and key metrics is recommended in larger cohorts.

The decision to reimage following extravasation in diagnostic nuclear medicine

The primary goal of diagnostic nuclear medicine is to provide complete and accurate reports without equivocation or disclaimers. If specific clinical questions cannot be answered because of radiopharmaceutical extravasation, the imaging study may have to be repeated. The decision to reimage is based on several factors including the diagnostic quality of the images, additional patient radiation dose, patient burden, and administrative constraints. Through process improvement efforts, nuclear medicine departments can significantly reduce the frequency of extravasation and thereby also the need for reimaging. Communication with the patient is important any time extravasation may impact their immediate or future care. The circumstances and potential ramifications should be explained, and patient concerns should be addressed. Although recent arguments have been made in favor of investigating and addressing only those extravasations which result in serious patient injury, patients and their referring physicians deserve to know any time their nuclear medicine study may have been impacted.

Active monitoring improves radiopharmaceutical administration quality

Introduction

In 2016, our center adopted technology to routinely monitor 18F-FDG radiopharmaceutical administrations. Within six months of following basic quality improvement methodology, our technologists reduced extravasation rates from 13.3% to 2.9% (p < 0.0001). These same technologists administer other radiopharmaceuticals (without monitoring technology) for general nuclear medicine procedures in a separate facility at the clinic. Our hypothesis was that they would apply 18F-FDG lessons-learned to 99mTc-MDP administrations and that 99mTc-MDP manual injection extravasation rate would be consistent with the ongoing 18F-FDG manual injection extravasation rate (3.4%). We tested our hypothesis by following the same quality improvement methodology and added monitoring equipment to measure extravasation rates for 99mTc-MDP administrations.

Results

816 99mTc-MDP administrations were monitored during 16-month period (four 4-month periods: A, B, C, D). Period A (first four months of active monitoring) extravasation rate was not statistically different from the Measure Phase extravasation rate of the previously completed PET/CT QI Project: 12.75% compared to 13.3% (p-0.7925). Period A extravasation rate was statistically different from Period C (months 9-12) extravasation rate and Period D (months 13-16) extravasation rate: 12.75% compared to 2.94% and to 3.43% (p < 0.0001). During Period C and D technologists achieved extravasation rates comparable to the longstanding manual 18F-FDG injection extravasation rate (3.4%).

Conclusion

Our initial hypothesis, that awareness of a problem and the steps need to correct it would result in process improvement, was not accurate. While those factors are important, they are not sufficient. Our findings suggest that active monitoring and the associated display of results are critical to quality improvement efforts to reduce and sustain radiopharmaceutical extravasation rates.

Intramuscular [18F]F-FDG Administration for Successful PET Imaging of Golden Hamsters in a Maximum Containment Laboratory Setting

Positron emission tomography (PET) is becoming an important tool for the investigation of emerging infectious diseases in animal models. Usually, PET imaging is performed after intravenous (IV) radiotracer administration. However, IV injections are difficult to perform in some small animals, such as golden hamsters. This challenge is particularly evident in longitudinal imaging studies, and even more so in maximum containment settings used to study high-consequence pathogens. We propose the use of intramuscular (IM) administration of 2-deoxy-2[¹⁸F]fluoro-D-glucose ([¹⁸F]F-FDG) for PET imaging of hamsters in a biosafety level 4 (BSL-4) laboratory setting. After [¹⁸F]F-FDG administration via IM or IV (through surgically implanted vascular access ports), eight hamsters underwent static or dynamic PET scans. Time-activity curves (TACs) and standardized uptake values (SUVs) in major regions of interest (ROIs) were used to compare the two injection routes. Immediately after injection, TACs differed between the two routes. At 60 min post-injection, [¹⁸F]F-FDG activity for both routes reached a plateau in most ROIs except the brain, with higher accumulation in the liver, lungs, brain, and nasal cavities observed in the IM group. IM delivery of [¹⁸F]F-FDG is an easy, safe, and reliable alternative for longitudinal PET imaging of hamsters in a BSL-4 laboratory setting.

Practical Tools for Patient-specific Characterization and Dosimetry of Radiopharmaceutical Extravasation

ABSTRACT

Extravasation during radiopharmaceutical injection may occur with a frequency of more than 10%. In these cases, radioactivity remains within tissue and deposits unintended radiation dose. Characterization of extravasations is a necessary step in accurate dosimetry, but a lack of free and publicly available tools hampers routine standardized analysis. Our objective was to improve existing extravasation characterization and dosimetry methods and to create and validate tools to facilitate standardized practical dosimetric analysis in clinical settings. Using Monte Carlo simulations, we calculated dosimetric values for sixteen nuclear medicine isotopes: 11 C, 64 Cu, 18 F, 67 Ga, 68 Ga, 123 I, 131 I, 111 In, 177 Lu, 13 N, 15 O, 82 Rb, 153 Sm, 89 Sr, 99m Tc, and 90 Y. We validated our simulation results against five logical alternative dose assessment methods. We then created three new characterization tools: a worksheet, a spreadsheet, and a web application. We assessed each tool by recalculating extravasation dosimetry results found in the literature and used each of the tools for patient cases to show clinical practicality. Average variation between our simulation results and alternative methods was 3.1%. Recalculation of published dosimetry results indicated an average error of 7.9%. Time required to use each characterization tool ranged from 1 to 5 min, and agreement between the three tools was favorable. We improved upon existing methods by creating new tools for characterization and dosimetry of radiopharmaceutical extravasation. These free and publicly available tools will enable standardized routine clinical analysis and benefit patient care, clinical follow-up, documentation, and event reporting.

Development of a classifier for [18F]fluorodeoxyglucose extravasation severity using semi-quantitative readings from topically applied detectors

Background

Radiotracer extravasations, caused largely by faulty tracer injections, can occur in up to 23% of ¹⁸F-fluorodeoxyglucose (FDG) PET/CT scans and negatively impact radiological review and tracer quantification. Conventional radiological assessment of extravasation severity on PET has limited performance (e.g., extravasations frequently resolve before scanning) and practical drawbacks. In this study, we develop a new topical detector-based FDG extravasation severity classifier, calibrated from semi-quantitative PET measurements, and assess its performance on human subjects.

Methods

A retrospective study examined patients whose FDG injections had been monitored as part of their standard workup for PET/CT imaging. Topical uncollimated gamma ray detectors were applied proximal to the injection site and on the same location on the opposing arm, and readings were acquired continuously during radiotracer uptake. Patients were imaged with their arms in the PET field of view and total extravasation activity quantified from static PET images through a volume of interest approach. The image-derived activities were considered ground truth and used to calibrate and assess quantification of topical detector readings extrapolated to the start of PET imaging. The classifier utilizes the calibrated detector readings to produce four extravasation severity classes: none, minor, moderate, and severe. In a blinded study, a radiologist qualitatively labeled PET images for extravasation severity using the same classifications. The radiologist’s interpretations and topical detector classifications were compared to the ground truth PET results.

Results

Linear regression of log-transformed image-derived versus topical detector tracer extravasation activity estimates showed a strong correlation (R² = 0.75). A total of 24 subject scans were cross-validated with the quantitatively based classifier through a leave-one-out methodology. For binary classification (none vs. extravasated), the topical detector classifier had the highest overall diagnostic performance for identifying extravasations. Specificity, sensitivity, accuracy, and positive predictive value were 100.0%, 80.0%, 95.8%, and 100.0%, respectively, for the topical detector classifier and 31.6%, 100.0%, 45.8%, and 27.8%, respectively, for the radiological analysis. The topical detector classifier, with an optimal detection threshold, produced a significantly higher Matthews correlation coefficient (MCC) than the radiological analysis (0.87 vs. 0.30).

Conclusions

The topical detector binary classifier, calibrated using quantitative static PET measurements, significantly improves extravasation detection compared to qualitative image analysis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40658-022-00488-6.

Detection of Excess Presence of 99m Tc-MDP Near Injection Site-A Case Report

Nuclear medicine extravasations and prolonged venous stasis may cause poor quality and quantification errors that can affect image interpretation and patient management. Radiopharmaceutical remaining near the administration site means that some portion of the radioactivity is not circulating as required for the prescribed uptake period. This case describes how detection of excess presence of ^99mTc-MDP near the injection site enabled the technologist to apply mitigation tactics early in the uptake process. It also suggests that detecting an extravasation or stasis early in the injection process can be important for image interpretation and minimizing radiation dose to tissue.

SimPET-An open online platform for the Monte Carlo simulation of realistic brain PET data. Validation for 18 F-FDG scans

Purpose

SimPET (www.sim‐pet.org) is a free cloud‐based platform for the generation of realistic brain positron emission tomography (PET) data. In this work, we introduce the key features of the platform. In addition, we validate the platform by performing a comparison between simulated healthy brain FDG‐PET images and real healthy subject data for three commercial scanners (GE Advance NXi, GE Discovery ST, and Siemens Biograph mCT).

Methods

The platform provides a graphical user interface to a set of automatic scripts taking care of the code execution for the phantom generation, simulation (SimSET), and tomographic image reconstruction (STIR). We characterize the performance using activity and attenuation maps derived from PET/CT and MRI data of 25 healthy subjects acquired with a GE Discovery ST. We then use the created maps to generate synthetic data for the GE Discovery ST, the GE Advance NXi, and the Siemens Biograph mCT. The validation was carried out by evaluating Bland‐Altman differences between real and simulated images for each scanner. In addition, SPM voxel‐wise comparison was performed to highlight regional differences. Examples for amyloid PET and for the generation of ground‐truth pathological patients are included.

Results

The platform can be efficiently used for generating realistic simulated FDG‐PET images in a reasonable amount of time. The validation showed small differences between SimPET and acquired FDG‐PET images, with errors below 10% for 98.09% (GE Discovery ST), 95.09% (GE Advance NXi), and 91.35% (Siemens Biograph mCT) of the voxels. Nevertheless, our SPM analysis showed significant regional differences between the simulated images and real healthy patients, and thus, the use of the platform for converting control subject databases between different scanners requires further investigation.

Conclusions

The presented platform can potentially allow scientists in clinical and research settings to perform MC simulation experiments without the need for high‐end hardware or advanced computing knowledge and in a reasonable amount of time.

Patient-specific Extravasation Dosimetry Using Uptake Probe Measurements

ABSTRACT

Extravasation is a common problem in radiopharmaceutical administration and can result in significant radiation dose to underlying tissue and skin. The resulting radiation effects are rarely studied and should be more fully evaluated to guide patient care and meet regulatory obligations. The purpose of this work was to show that a dedicated radiopharmaceutical injection monitoring system can help clinicians characterize extravasations for calculating tissue and skin doses. We employed a commercially available radiopharmaceutical injection monitoring system to identify suspected extravasation of 18F-fluorodeoxyglucose and 99mTc-methylene diphosphonate in 26 patients and to characterize their rates of biological clearance. We calculated the self-dose to infiltrated tissue using Monte Carlo simulation and standard MIRD dosimetry methods, and we used VARSKIN software to calculate the shallow dose equivalent to the epithelial basal-cell layer of overlying skin. For 26 patients, injection-site count rate data were used to characterize extravasation clearance. For each, the absorbed dose was calculated using representative tissue geometries. Resulting tissue-absorbed doses ranged from 0.6 to 11.2 Gy, and the shallow dose equivalent to a 10 cm2 area of adjacent skin in these patients ranged from about 0.1 to 5.4 Sv. Extravasated injections of radiopharmaceuticals can result in unintentional doses that exceed well-established radiation protection and regulatory limits; they should be identified and characterized. An external injection monitoring system may help to promptly identify and characterize extravasations and improve dosimetry calculations. Patient-specific characterization can help clinicians determine extravasation severity and whether the patient should be followed for adverse tissue reactions that may present later in time.

Topical sensor metrics for 18F-FDG positron emission tomography dose extravasation

INTRODUCTION

Extravasation or partial extravasation of the positron emission tomography (PET) tracer negatively effects image quality in PET and the accuracy of the standard uptake value (SUV). A commercially available topical sensor has been validated using a number of metrics to characterise injection quality. This evaluation explores contributing factors for extravasation and refines metrics to predict extravasation based on the time-activity-curves (TAC) of the topical sensor device.

METHODS

A multi-site, multi-national pooling of 18F FDG PET/CT data was undertaken with 863 patients from 6 sites in the USA and 2 sites in Australia. A number of dose migration metrics determined with topical application of Lara sensors were retrospectively analysed using conventional statistical analysis. Deeper insights into the complex relationship between variables was further explored using an artificial neural network.

RESULTS

Extravasation was independently predicted by the time taken for the injection sensor counts to reach double the counts of the reference sensor (tc50), the normalised difference between injection and reference sensors counts at 4 min post injection (ndAvgN), or the ratio of injection sensor counts to reference sensor counts at the end of data collection (CEnd ratio). The algorithm developed using the artificial neural network produced 100% sensitivity and 100% specificity against grounded truth for detecting extravasation by weighting and scaling these 3 key metrics; CEnd ratio, ndAvgN and tc50.

CONCLUSION

Partial extravasation of a PET dose is readily detected and differentiated using TAC metrics and these metrics could provide deeper insight into the impact of partial extravasation on image quality or quantitation. Further validation of key metrics developed in this study are recommended in a larger and more diverse cohort.

IMPLICATIONS FOR PRACTICE

Partial extravasation undermines image quality and accuracy of quantitation, impacting efficacy of outcomes for patients. Characterisation of extravasation informs decision making to optimise protocol and procedure, enhancing patient outcomes. Awareness provides the opportunity for education and training to minimise impact. The information can be used to drive policy and regulations to support improved techniques in practice.

Topical Sensor for the Assessment of PET Dose Administration: Metric Performance with an Autoinjector

Extravasation or partial extravasation of the radiopharmaceutical dose in PET can undermine SUV and image quality. A topical sensor has been validated using several metrics to characterize injection quality after manual injection. The performance of these metrics for autoinjector administration has been assessed. Methods: A single PET/CT scanner at a single site was used to characterize injections using an autoinjector with standardized apparatus, flush volume, and infusion rate (1-min infusion followed by 2 syringe flushes) for ¹⁸F-FDG, ⁶⁸Ga-prostate-specific membrane antigen, and ⁶⁸Ga-DOTATATE. In total, 296 patients with topical application of sensors were retrospectively analyzed using conventional statistical analysis and an artificial neural network. Results: Partial extravasation was noted in 1.3% of studies, with 9.1% (inclusive of partial extravasation) identified to have an injection anomaly (e.g., venous retention). Extravasation was independently predicted by the time that elapsed as the counts recorded by the injection sensor fell from the maximum value to within 200% of the reference sensor counts greater than 1,200 s; as the difference in counts for injection and reference sensors, normalized by dose, from 4 min after injection greater than 25; and as the ratio of the average counts per second recorded by the injection sensor at the end of a monitoring period to those of the reference sensor greater than 2. Conclusion: Extravasation and partial extravasation of PET doses are readily detected and differentiated using time-activity curve metrics. The metrics can provide the insight that could inform image quality or SUV accuracy issues. Further validation of key metrics is recommended in a larger and more diverse cohort.

Topical Sensor for the Assessment of Injection Quality for 18F-FDG, 68Ga-PSMA and 68Ga-DOTATATE Positron Emission Tomography

INTRODUCTION

Calculation of the standard uptake value (SUV) and image quality in positron emission tomography (PET) hinges on accurate dose delivery. Extravasation or partial extravasation of the radiopharmaceutical dose can undermine SUV and image quality, and contribute to unnecessary imaging (time and CT dose). Topical sensor characterisation of injections has been reported, with extravasation rates ranging from 9% to 23% for 18F-FDG after manual injection.

METHOD

A single site, single PET/CT scanner was used to characterise injections using an autoinjector with standardised apparatus, flush volume and infusion rate using 18F-FDG, 68Ga-PSMA and 68Ga-DOTATATE; more reflective of Australian PET facilities. 296 patients with topical application of LARA sensors were retrospectively analysed.

RESULTS

Only 1.1% of studies showed evidence of partial dose extravasation. In total, 9.1% were identified to have an injection anomaly (including venous retention). No statistically significant differences were noted across the radiopharmaceuticals for demographic data. Although not demonstrating a statistically significant correlation, there was more extravasated doses associated with female patients (P = .334), right side (P = .372), and hand injections (P = .539). Extravasation was independent of dose administered (P = .495), the radiopharmaceutical (P = .887), who injected the dose (P = .343), height (P = .438), weight (P = .607) or age (P = .716). Extravasation was associated with higher glucose levels (P < .001), higher t-half (P = .019) and higher aUCR10, tc50, aUCR1 and c1 (all P < .001).

CONCLUSION

Topical monitoring and characterisation of PET dose administration is possible and practical with the LARA device. Extravasation and partial extravasation of PET doses are not only readily detected but they are also preventable. The LARA device can provide the insights into variables that could eliminate extravasation as a cause of image quality or SUV accuracy issues.

Assessing and Reducing Positron Emission Tomography/Computed Tomography Radiotracer Infiltrations: Lessons in Quality Improvement and Sustainability

PURPOSE

Accurate administration of radiotracer dose is essential to positron emission tomography (PET) image quality and quantification. Misadministration (infiltration) of the dose can affect PET/computed tomography results and lead to unnecessary or inappropriate treatments and procedures. Quality control efforts ensure accuracy of the administered dose; however, they fail to ensure complete delivery of the dose into the patient's circulation. We used new technology to assess and improve infiltration rates and evaluate sustainability.

METHODS

Injection quality was measured, improved, and sustained during our participation in a multicenter quality improvement project using Define, Measure, Analyze, Improve, Control methodology. Five technologists monitored injection quality in the Measure and Improve phases. After seven new technologists joined the team in the Control phase, infiltration rates were recalculated, controlling for technologist- and patient-level correlations, and comparisons were made between these two groups of technologists.

RESULTS

In the Measure phase, five technologists monitored 263 injections (13.3% infiltration rate). Nonantecubital fossa injections had a higher probability of infiltration than antecubital fossa injections. After implementing a quality improvement plan (QIP), the same technologists monitored 278 injections in the Improve phase (2.9% infiltration rate). The 78% decrease in infiltration rate was significant (P < .001) as was the decrease in nonantecubital fossa infiltrations (P = .0025). In the Control phase, 12 technologists monitored 1,240 injections (3.1% infiltration rate). The seven new technologists had significantly higher rates of infiltration (P = .017).

CONCLUSION

A QIP can significantly improve and sustain injection quality; however, ongoing monitoring is needed as new technologists join the team.

Quality Improvement Initiatives to Assess and Improve PET/CT Injection Infiltration Rates at Multiple Centers

PET/CT radiotracer infiltration is not uncommon and is often outside the imaging field of view. Infiltration can negatively affect image quality, image quantification, and patient management. Until recently, there has not been a simple way to routinely practice PET radiopharmaceutical administration quality control and quality assurance. Our objectives were to quantify infiltration rates, determine associative factors for infiltration, and assess whether rates could be reduced at multiple centers and then sustained. Methods: A “design, measure, analyze, improve, and control” quality improvement methodology requiring novel technology was used to try to improve PET/CT injection quality. Teams were educated on the importance of quality injections. Baseline infiltration rates were measured, center-specific associative factors were analyzed, team meetings were held, improvement plans were established and executed, and rates remeasured. To ensure that injection-quality gains were retained, real-time feedback and ongoing monitoring were used. Sustainability was assessed. Results: Seven centers and 56 technologists provided data on 5,541 injections. The centers’ aggregated baseline infiltration rate was 6.2% (range, 2%–16%). On the basis of their specific associative factors, 4 centers developed improvement plans and reduced their aggregated infiltration rate from 8.9% to 4.6% (P < 0.0001). Ongoing injection monitoring showed sustainability. Significant variation was found in center- and technologist-level infiltration rates (P < 0.0001 and P = 0.0020, respectively). Conclusion: A quality improvement approach with new technology can help centers measure infiltration rates, determine associative factors, implement interventions, and improve and sustain injection quality. Because PET/CT images help guide patient management, the monitoring and improvement of radiotracer injection quality are important.

Usefulness of Topically Applied Sensors to Assess the Quality of 18F-FDG Injections and Validation Against Dynamic Positron Emission Tomography (PET) Images

Background: Infiltrations of 18F-fluorodeoxyglucose (FDG) injections affect positron emission tomography/computed tomography (PET/CT) image quality and quantification. A device using scintillation sensors (Lucerno Dynamics, Cary, NC) provides dynamic measurements acquired during FDG uptake to identify and characterize radioactivity near the injection site prior to patient imaging. Our aim was to compare sensor measurements against dynamic PET image acquisition, our proposed reference in assessing injection quality during the uptake period. Methods: Subjects undergoing routine FDG PET/CT imaging were eligible for this Institutional Review Board approved prospective study. After providing informed consent, subjects had sensors topically placed on their arms. FDG was injected into subjects' veins directly on the PET imaging table. Dynamic images of the injection site were acquired during 45 min of the uptake period. These dynamic image acquisitions and subjects' routine standard static images were evaluated by nuclear medicine physicians for abnormal FDG accumulation near the injection site. Sensor measurements were interpreted independently by Lucerno staff. Dynamic image acquisition interpretation results were compared to the sensor measurement interpretations and to static image interpretations. Results: Twenty-four subjects were consented and enrolled. Data from 21 subjects were gathered. During dynamic image acquisition review, physicians interpreted 4 subjects with no FDG accumulation at the injection site, whereas 17 showed evidence of accumulation. In 10 of the 17 cases that showed FDG accumulation, the FDG presence at the injection site resolved completely during uptake corresponding to venous stasis, the temporary sequestration of blood from circulation. Static image interpretation agreed with dynamic images interpretation in 11/21 (52%) subjects. Sensor measurement interpretations agreed with the dynamic images interpretations in 18/21 (86%) subjects. Conclusions: Sensor measurements can be an effective way to identify and characterize infiltrations and venous stasis. Comparable to an infiltration, venous stasis may produce spurious and clinically meaningful measurement bias and possibly even scan misinterpretation. Since the quality and quantification of PET/CT studies are of clinical importance, sensor measurements acquired during the FDG uptake may prove to be a useful quality control measure to reduce infiltration rates and potentially improve patient care. Registration: Clinicaltrials.gov, Identifier: NCT03041090.

Impact of an 18F-FDG PET/CT Radiotracer Injection Infiltration on Patient Management-A Case Report

Major management decisions in patients with solid tumors and lymphomas are often based on 18F-fluorodeoxyglucose (18F-FDG) PET/CT. The misadministration of 18F-FDG outside the systemic circulation can have an adverse impact on this test's sensitivity (1) and is not uncommon (2-7). This report describes how an 18F-FDG misadministration led to a repeat PET/CT study, resulting in the visualization of distant metastases that changed the original treatment plan. The findings suggest that routine injection monitoring is indicated whenever sensitivity is critical, and support claims that infiltrations can confound interpretation of semi-quantitative PET outcome measures in patients who are followed longitudinally (2).

Consequences of radiopharmaceutical extravasation and therapeutic interventions: a systematic review

Purpose

Radiopharmaceutical extravasation can potentially lead to severe soft tissue damage, but little is known about incidence, medical consequences, possible interventions, and effectiveness of these. The aims of this study are to estimate the incidence of extravasation of diagnostic and therapeutic radiopharmaceuticals, to evaluate medical consequences, and to evaluate medical treatment applied subsequently to those incidents.

Methods

A sensitive and elaborate literature search was performed in Embase and PubMed using the keywords “misadministration”, “extravasation”, “paravascular infiltration”, combined with “tracer”, “radionuclide”, “radiopharmaceutical”, and a list of keywords referring to clinically used tracers (i.e. “Technetium-99m”, “Yttrium-90”). Reported data on radiopharmaceutical extravasation and applied interventions was extracted and summarised.

Results

Thirty-seven publications reported 3016 cases of diagnostic radiopharmaceutical extravasation, of which three cases reported symptoms after extravasation. Eight publications reported 10 cases of therapeutic tracer extravasation. The most severe symptom was ulceration. Thirty-four different intervention and prevention strategies were performed or proposed in literature.

Conclusions

Extravasation of diagnostic radiopharmaceuticals is common. ^99mTc, ¹²³I, ¹⁸F, and ⁶⁸Ga labelled tracers do not require specific intervention. Extravasation of therapeutic radiopharmaceuticals can give severe soft tissue lesions. Although not evidence based, surgical intervention should be considered. Furthermore, dispersive intervention, dosimetry and follow up is advised. Pharmaceutical intervention has no place yet in the immediate care of radiopharmaceutical extravasation.

Estimation of activity of administered 18F-fluorodeoxyglucose by measurement of the dose equivalent rate on the right temporal region of the head

Background

Positron emission tomography (PET) with ¹⁸F-fluorodeoxyglucose (FDG) is now a routine procedure for the management of cancer patients. Intravenous administration of FDG is sometimes halted due to troubles. In such cases, estimations of the FDG dosage injected prior to halting administration may be helpful. We have established a method of estimating the activity of FDG to patients on the basis of the dose equivalent rate on the surface of the right temporal region of the head. The correlation of actual administered dosage with independent variables, such as the dose equivalent rate on the right temporal region of the head, age, sex, and body weight, was analyzed using multiple regression analysis to obtain linear, quadratic, and cubic regression equations.

Results

When entering independent variables, the cubic regression equation could be used to estimate an administered dosage with an accuracy of ±10 % for 62 % of all patients and ±20 % for 90 % of all patients.

Conclusions

We conclude that this method is useful for estimating the administered dosage from the dose equivalent rate on the temporal region of the head.

The Strategies to Homogenize PET/CT Metrics: The Case of Onco-Haematological Clinical Trials

Positron emission tomography (PET) has been a widely used tool in oncology for staging lymphomas for a long time. Recently, several large clinical trials demonstrated its utility in therapy management during treatment, paving the way to personalized medicine. In doing so, the traditional way of reporting PET based on the extent of disease has been complemented by a discrete scale that takes in account tumour metabolism. However, due to several technical, physical and biological limitations in the use of PET uptake as a biomarker, stringent rules have been used in clinical trials to reduce the errors in its evaluation. Within this manuscript we will describe shortly the evolution in PET reporting, examine the main errors in uptake measurement, and analyse which strategy the clinical trials applied to reduce them.

Towards real-time topical detection and characterization of FDG dose infiltration prior to PET imaging

PURPOSE

To dynamically detect and characterize ¹⁸F-fluorodeoxyglucose (FDG) dose infiltrations and evaluate their effects on positron emission tomography (PET) standardized uptake values (SUV) at the injection site and in control tissue.

METHODS

Investigational gamma scintillation sensors were topically applied to patients with locally advanced breast cancer scheduled to undergo limited whole-body FDG-PET as part of an ongoing clinical study. Relative to the affected breast, sensors were placed on the contralateral injection arm and ipsilateral control arm during the resting uptake phase prior to each patient's PET scan. Time-activity curves (TACs) from the sensors were integrated at varying intervals (0-10, 0-20, 0-30, 0-40, and 30-40 min) post-FDG and the resulting areas under the curve (AUCs) were compared to SUVs obtained from PET.

RESULTS

In cases of infiltration, observed in three sensor recordings (30 %), the injection arm TAC shape varied depending on the extent and severity of infiltration. In two of these cases, TAC characteristics suggested the infiltration was partially resolving prior to image acquisition, although it was still apparent on subsequent PET. Areas under the TAC 0-10 and 0-20 min post-FDG were significantly different in infiltrated versus non-infiltrated cases (Mann-Whitney, p < 0.05). When normalized to control, all TAC integration intervals from the injection arm were significantly correlated with SUV_peak and SUV_max measured over the infiltration site (Spearman ρ ≥ 0.77, p < 0.05). Receiver operating characteristic (ROC) analyses, testing the ability of the first 10 min of post-FDG sensor data to predict infiltration visibility on the ensuing PET, yielded an area under the ROC curve of 0.92.

CONCLUSIONS

Topical sensors applied near the injection site provide dynamic information from the time of FDG administration through the uptake period and may be useful in detecting infiltrations regardless of PET image field of view. This dynamic information may also complement the static PET image to better characterize the true extent of infiltrations.

Effect of (18)F-fluorodeoxyglucose extravasation on time taken for tumoral uptake to reach a plateau: animal and clinical PET analyses

OBJECTIVE

The present study aimed to investigate the effect of (18)F-fluorodeoxyglucose (FDG) extravasation on the time taken for tumoral uptake to reach a plateau.

METHODS

For the animal experiment, FDG extravasation was conducted in the tails of HCT116 tumor-bearing xenograft mice models in three groups (no extravasation, 40 % extravasation, and 80 % extravasation; n = 5, each). Dynamic positron emission tomography (PET) images were acquired over a period of 2 h following injection. Time-activity curves for FDG in the tails and tumors were calculated. For the clinical experiment, 22 patients (male:female, 14:8; age range, 70.8 ± 9.2 years) were subjected to PET/computed tomography (PET/CT) 1 h after the injection of FDG. The inclusion criteria were as follows: (1) submitted to both whole-body and subsequent regional scanning; (2) entire extravasation activity visualized in the whole-body images; (3) tumor visualized on both whole-body and additional regional images; and (4) status of tumor either confirmed by biopsy or clinically suspected for malignancy. The standardized uptake values (SUVs) of the tumors (on the whole-body and additional PET images) and extravasation sites were recorded.

RESULTS

There were no significant differences in the time taken for tumoral uptake to reach a plateau and that to reach minimum activity at the extravasation site among the three groups of mice. However, the mean tumoral activity and activity at the extravasation site were negatively correlated at 1 h post-injection. According to the clinical PET findings, the differences in SUV between the whole-body and regional images were not significantly correlated with the interval between injection of FDG and start of whole-body scanning, interval between the start of whole-body scanning and start of regional scanning, extravasation volume, maximum SUV of the extravasation site, or total activity at the extravasation site.

CONCLUSIONS

The time taken for tumoral uptake to reach a plateau is not affected by extravasation, even at extensive degrees. Thus, in routine practice, the imaging time of approximately 60 min post-injection need not be modified even if extravasation is identified. However, tumor SUV may be underestimated in cases of extravasation.

Impact and correction of the bladder uptake on 18 F-FCH PET quantification: a simulation study using the XCAT2 phantom

The spill-in counts from neighbouring regions can significantly bias the quantification over small regions close to high activity extended sources. This effect can be a drawback for (18)F-based radiotracers positron emission tomography (PET) when quantitatively evaluating the bladder area for diseases such as prostate cancer. In this work, we use Monte Carlo simulations to investigate the impact of the spill-in counts from the bladder on the quantitative evaluation of prostate cancer when using (18)F-Fluorcholine (FCH) PET and we propose a novel reconstruction-based correction method. Monte Carlo simulations of a modified version of the XCAT2 anthropomorphic phantom with (18)F-FCH biological distribution, variable bladder uptake and inserted prostatic tumours were used in order to obtain simulated realistic (18)F-FCH data. We evaluated possible variations of the measured tumour Standardized Uptake Value (SUV) for different values of bladder uptake and propose a novel correction by appropriately adapting image reconstruction methodology. The correction is based on the introduction of physiological background terms on the reconstruction, removing the contribution of the bladder to the final image. The bladder is segmented from the reconstructed image and then forward-projected to the sinogram space. The resulting sinograms are used as background terms for the reconstruction. SUV max and SUV mean could be overestimated by 41% and 22% respectively due to the accumulation of radiotracer in the bladder, with strong dependence on bladder-to-lesion ratio. While the SUVs measured under these conditions are not reliable, images corrected using the proposed methodology provide better repeatability of SUVs, with biases below 6%. Results also showed remarkable improvements on visual detectability. The spill-in counts from the bladder can affect prostatic SUV measurements of (18)F-FCH images, which can be corrected to less than 6% using the proposed methodology, providing reliable SUV values even in the presence of high radioactivity accumulation in the bladder.

The total amount of uptake may affect the input function: a theoretic approach about 18F-FDG PET imaging

INTRODUCTION

The aim of this theoretic approach is to establish an analytical relationship between the total amount of uptake (TAU), either pathological or physiological, and the time constants "αi" that describe the time decay of the tracer input function (IF). The proposed approach uses parameters of a (population-based) arterial plasma IF for 18 F-FDG PET imaging.

METHODS

A previously published formula provides an estimate of the ratio "p" of 18 F-FDG molecules that are irreversibly trapped in an 18 F-FDG-positive tissue during a whole PET examination, to the number of injected molecules. Then, the change in the magnitude of the IF time constants is derived, involving a corrective procedure.

RESULTS

Trapping of injected tracer molecules affects each αi that is increased by a factor of 1/(1-p), with p ranging between zero and, theoretically, less than 1. This result is illustrated in a patient showing an intense uptake in the mediastinum at initial staging of a diffuse large B-cell lymphoma (DLBCL).

CONCLUSIONS

An analytical relationship between TAU and the IF time constants is available in 18 F-FDG PET imaging, showing that TAU may actually affect the IF.

Simulated FDG-PET studies for the assessment of SUV quantification methods

AIM

To study in detail the accuracy and repeatability of three commonly used methods for SUV estimation in solitary pulmonary nodules.

MATERIAL AND METHODS

We have designed a realistic framework based on simulated FDG-PET acquisitions from an anthropomorphic activity model that included solitary pulmonary nodules (different sizes) of well-known SUV. This framework enables us to compare the SUV values obtained from the reconstructed PET images with the real SUV values. Three commonly used methods (SUVmax, SUVmean and SUV50) were used to estimate the tumor activity.

RESULTS

Our results showed the tumor activity was overestimated using SUVmax and clearly subestimated using SUVmean. Instead, the quantification of SUV50 showed great agreement with the simulated tumor activity and only slight subestimation was found for very small lesions. On the other hand, SUVmean showed better performance than SUV50 in terms of repeatability, providing variabilities below 5% for all tumor sizes and for injected doses as low as 111 MBq.

CONCLUSIONS

Our findings showed that SUV50 provided better performance for estimating accurately tumor SUV values in pulmonary nodules, but SUVmean showed better results in terms of repeatability.