Patient-specific Extravasation Dosimetry Using Uptake Probe Measurements

Dosimetric and biological impact of activity extravasation of radiopharmaceuticals in PET imaging

BACKGROUND

The increasing use of nuclear medicine and PET imaging has intensified scrutiny of radiotracer extravasation. To our knowledge, this topic is understudied but holds great potential for enhancing our understanding of extravasation in clinical PET imaging.

PURPOSE

This work aims to (1) quantify the absorbed doses from radiotracer extravasation in PET imaging, both locally at the site of extravasation and with the extravasation location as a source of exposure to bodily organs and (2) assess the biological ramifications within the injection site at the cellular level.

METHODS

A radiation dosimetry simulation was performed using a whole-body 4D Extended Cardiac-Torso (XCAT) phantom embedded in the GATE Monte Carlo platform. A 10-mCi dose of 18F-FDG was chosen to simulate a typical clinical PET scan scenario, with 10% of the activity extravasated in the antecubital fossa of the right arm of the phantom. The extravasation volume was modeled as a 5.5 mL rectangle in the hypodermal layer of skin. Absorbed dose contributions were calculated for the first two half-lives, assuming biological clearance thereafter. Dose calculations were performed as absorbed doses at the organ and skin levels. Energy deposition was simulated both at the local extravasation site and in multiple organs of interest and converted to absorbed doses based on their respective masses. Each simulation was repeated ten times to estimate Monte Carlo uncertainties. Biological impacts on cells within the extravasated volume were evaluated by randomizing cells and exposing them to a uniform radiation source of 18F and 68Ga. Particle types, their energies, and direction cosines were recorded in phase space files using a separate Geant4 simulation to characterize their entry into the nucleus of the cellular volume. Subsequently, the phase space files were imported into the TOPAS-nBio simulation to assess the extent of DNA damage, including double-strand breaks (DSBs) and single-strand breaks (SSBs).

RESULTS

Organ-level dosimetric estimations are presented for 18F and 68Ga radionuclides in various organs of interest. With 10% extravasation, the hypodermal layer of the skin received the highest absorbed dose of 1.32 ± 0.01 Gy for 18F and 0.99 ± 0.01 Gy for 68Ga. The epidermal and dermal layers received absorbed doses of 0.07 ± 0.01 Gy and 0.13 ± 0.01 Gy for 18F, and 0.14 ± 0.01 Gy and 0.29 ± 0.01 Gy for 68Ga, respectively. In the extravasated volume, 18F caused an average absorbed dose per nucleus of 0.17 ± 0.01 Gy, estimated to result in 10.58 ± 0.50 DSBs and 268.11 ± 12.43 SSBs per nucleus. For 68Ga, the absorbed dose per nucleus was 0.11 ± 0.01 Gy, leading to an estimated 6.49 ± 0.34 DSBs and 161.24 ± 8.12 SSBs per nucleus. Absorbed doses in other organs were on the order of micro-gray (µGy).

CONCLUSION

The likelihood of epidermal erythema resulting from extravasation during PET imaging is low, as the simulated absorbed doses to the epidermis remain below the thresholds that trigger such effects. Moreover, the organ-level absorbed doses were found to be clinically insignificant across various simulated organs. The minimal DNA damage at the extravasation site suggests that long-term harm, such as radiation-induced carcinogenesis, is highly unlikely.

Treatment of [99mTc]Tc-hydroxy-diphosphonate ([99mTc]Tc-HDP) extravasation using hyaluronidase

Extravasation of 99mTc-labeled radiopharmaceuticals is generally considered to require no specific intervention. In the presented case, the use of hyaluronidase could have minimized the adverse effects resulting from such an extravasation. Currently, no guidelines exist regarding the use of hyaluronidase after extravasation of [99mTc]Tc-HDP. Considering the low risk of administering hyaluronidase, it should be considered to limit the risk of injury after extravasation of [99mTc]Tc-HDP.

Case Report: Radiopharmaceutical extravasation, radiation paranoia, and chilling effect

The Society of Nuclear Medicine and Molecular Imaging (SNMMI) has publicly commented that they do not support the reporting of large extravasations to patients or regulatory bodies. The comment cites recently published articles suggesting that extravasations are infrequent and not severe. The comment stresses the importance of ensuring patients are not apprehensive or resistant to nuclear medicine procedures because of "radiation paranoia" and a "chilling effect" that can result from misinformation. Radiation paranoia and chilling effect are not defined, and there are no references to specific misinformation. Our experiences and this case suggest the comment may be incongruent with real-world clinical experiences. Our severe case, at a center with a long-standing focus on reducing radiopharmaceutical extravasation, suggests these events can still happen, can be significant, and should be shared with our patients. Our experiences also suggest that being transparent with patients builds trust. We are concerned that a reluctance to recognize the true frequency of extravasations and their severity may create distrust in the relationship between the nuclear medicine community and patients.

Radiopharmaceutical extravasation in bone scintigraphy: a cross-sectional study

OBJETIVES

Tc-99m Hydroxymethylene diphosphonate (HMDP) bone scintigraphy is commonly used to diagnose bone disorders. We aimed to quantify and characterize the occurrence of radiopharmaceutical extravasation in bone scintigraphy, using Tc-99m HMDP, as well as to compare the visual classification of the events with an independent analysis using image processing software.

METHODS

We conducted a cross-sectional study, using data from a total of 400 (9.1%) exams, randomly selected from all the procedures performed in 2018 in the Portuguese Institute of Oncology of Porto, Portugal. Prevalence estimate and the corresponding 95% confidence interval (CI) was computed for the presence of extravasation. Odds ratios and 95% CI were computed to quantify the association between demographic and clinical characteristics, and the occurrence of extravasation.

RESULTS

The prevalence of Tc-99m HMDP extravasation was 26.5% (95% CI: 22.4-31.0). Those from an inpatient setting had almost seven-fold higher odds of extravasation than those from an outpatient setting. When the wrist was used for administration, there was three times more odds of extravasation when compared to the use of hand. There were statistically significant differences in the median scores of extravasations severity obtained from image processing software according to the different grades attributed by visual appreciation ( P  < 0.001).

CONCLUSION

Tc-99m HMDP extravasation occurred in one out of four patients, being more frequent among those from an inpatient setting and when the wrist was used for administration. Visual appreciation of the extravasation seems to be acceptable to classify its severity.

To tell or not to tell … the patient about potential harm

Extravasation, as distinct from infiltration, is when a potentially toxic agent (e.g., radiographic contrast, chemotherapy, anesthesia or radionuclide) is unintentionally administered to the surrounding tissue instead of directly into the vein. There is an expectation for vascular access in interventional medicine across nearly all specialties that this high frequency, study/treatment critical procedure needs to occur with rare failure and that this failure rate should be characterized in quality assurance. This opinion piece, written by a family practitioner who has served as the chief medical officer for a not-for-profit payer, reflects on our responsibility to be aware as clinicians of known potential harm and disclose to patients before a risk has occurred and if harm has occurred. In this paper, clinical obligations of reporting will be reviewed, which are necessary to maintain and enhance our trust with our patients. In the second half, the perspectives of a not-for-profit payer chief medical officer will be considered.

Radiopharmaceutical extravasations: a twenty year mini-review

Interest and research into radiopharmaceutical extravasation concepts has risen with the increase in use of radiopharmaceutical therapies, growing access to novel molecular imaging agents, and recent regulatory controversies. This mini-review will examine the literature of the last twenty years to summarize the history of radiopharmaceutical extravasations, determine key trends in imaging and therapies, and highlight critical gaps in research that currently exist. The intent of this work is to provide a summary of this complex topic that helps build awareness and promotes new innovations in this interesting aspect of theranostic radiopharmaceuticals.

Multicenter Evaluation of Frequency and Impact of Activity Infiltration in PET Imaging, Including Microscale Modeling of Skin-Absorbed Dose

There has been significant recent interest in understanding both the frequency of nuclear medicine injection infiltration and the potential for negative impact, including skin injury. However, no large-scale study has yet correlated visualized injection site activity with actual activity measurement of an infiltrate. Additionally, current skin dosimetry approaches lack sufficient detail to account for critical factors that impact the dose to the radiosensitive epidermis. Methods: From 10 imaging sites, 1,000 PET/CT patient studies were retrospectively collected. At each site, consecutive patients with the injection site in the field of view were used. The radiopharmaceutical, injected activity, time of injection and imaging, injection site, and injection method were recorded. Net injection site activity was calculated from volumes of interest. Monte Carlo image-based absorbed dose calculations were performed using the actual geometry from a patient with a minor infiltration. The simulation model used an activity distribution in the skin microanatomy based on known properties of subcutaneous fat, dermis, and epidermis. Simulations using several subcutaneous fat-to-dermis concentration ratios were performed. Absorbed dose to the epidermis, dermis, and fat were calculated along with relative γ- and β-contributions, and these findings were extrapolated to a hypothetical worst-case (470 MBq) full-injection infiltration. Results: Only 6 of 1,000 patients had activity at the injection site in excess of 370 kBq (10 μCi), with no activities greater than 1.7 MBq (45 μCi). In 460 of 1,000 patients, activity at the injection site was clearly visualized. However, quantitative assessment of activities averaged only 34 kBq (0.9 μCi), representing 0.008% of the injected activity. Calculations for the extrapolated 470-MBq infiltration resulted in a hypothetical absorbed dose to the epidermis of below 1 Gy, a factor of 2 lower than what is required for deterministic skin reactions. Analysis of the dose distribution demonstrates that the dermis acts as a β-shield for the radiation-sensitive epidermis. Dermal shielding is highly effective for low-energy 18F positrons but less so with the higher-energy positrons of 68Ga. Conclusion: When quantitative activity measurement criteria are used rather than visual, the frequency of PET infiltration appears substantially below frequencies previously published. Shallow doses to the epidermis from infiltration events are also likely substantially lower than previously reported because of absorption of β-particles in the dermis.

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.

Insights into handling and delivery of Y-90 radioembolization therapies

Introduction

The use of Y-90 radioembolization techniques has become a standard tool for the treatment of liver cancer and metastatic diseases that result in liver lesions. As there are only two approved forms of radioembolization therapy, the procedures for use are also fairly standardized even though exact international and interdepartmental procedures can vary. What has been less published over the years are the nuanced differences in delivery techniques and handling of the two available Y90 radioembolization therapies. This paper seeks to examine various aspects of delivery techniques, product handling, and radiation exposure that differ between the available and approved products. Understanding these differences can assist with providing more efficient treatment, confirmation of accurate therapy, more informed handling of the products, and improved training of physicians and other hospital staff.

Methods

Two commercially available and approved radioembolization devices were compared to assess nuanced, but key differences between the available products regarding therapy delivery, handling of the products, and radiation exposure to patients and staff. This work is broken into two sections: (1) Therapy Delivery, (2) Radiation Safety. Therapy delivery characteristics were assessed by using an external radiation detector system with detectors placed inside of each delivery system facing the dose vial and on the output catheter lines to the patient. Additional detectors were placed near the liver of the patient and on top of the foot to measure extremities. Data were acquired continuously throughout therapy delivery to collect time activity curves (TACs) for the characterization of each therapy. These data were analyzed to assess if (a) real-time monitoring of radiation could be used to provide an accurate assessment of residual dose before the patient leaves the procedure room, and (b) can dose delivery characteristics be observed that enable improved training and quality control. Calculation of residual dose using the external detector TACs was performed by analyzing initial and final activity peaks to determine measured count rate differences. Radiation safety aspects were assessed by monitoring radiation exposure to staff handling each of the available therapy products. Nuclear medicine technologists and interventional radiology physician body and hand doses were measured for each delivered therapy using standard body and ring dosimeters. The TACs noted above collected for the liver and extremities were used to assess if any off-target or leached Y90 activity could be detected for each therapy. Blood was collected at times before, during, and after treatment and then counted on a gamma counter to assess differences in free Y90 circulating in the blood. Each patient in this study also received a post-treatment whole-body PET/CT at 2-4 h post-infusion to assess for any aggregate free Y90 deposition that may have resulted from circulating free Y90 in the subject following therapy.

Results

Calculations of residual dose in the vial following therapy using the real-time detection methods resulted in values that were not statistically different from the values calculated by nuclear medicine following the procedure ( p > 0.05 ). Real-time collection of dose delivery data enabled observation of key characteristics related to each delivery method. For SIR-spheres procedures, the cycle of pushing the dose and visualizing with fluoro can easily be seen with each push resulting in a smaller and smaller peak with intermittent fluoroscopy pulses. TheraSpheres infusions show a rapid bolus with nearly all of the measurable injected activity being infused in the first push of the dose. Staff radiation exposure assessments showed statistically significant differences between glass and resin spheres for hand doses of physicians and technologists (p > 0.05), but no statistical difference between body doses for both products ( p > 0.05 ). Assessments of free Y90 circulating during therapy showed that patients undergoing therapies with resin spheres had post-infusion blood levels that were 120% higher than pre-infusion levels while glass sphere therapy patients only saw a 7% rise in post-infusion blood levels. The coefficients of variation (COVs) across glass sphere measurements pre, during, and post, were only 0.008 while resin sphere measures saw much greater variability with a COV of 0.45. Both glass and resin therapies showed blood levels at 2-4 h post-injection to be similar to levels measured pre-injection. Neither therapy showed any signs of focal aggregation at 2-4 h post-infusion on whole-body PET/CT.

Conclusion

Although glass and resin radioembolization therapies are similar, they both have unique characteristics related to their administration and handling by staff. Understanding the nuances can assist in providing more efficient delivery, better staff education, and reducing radiation exposure to everyone involved with these therapies. The use of near real-time monitoring is feasible and can be used to obtain critical information about the delivery success of a therapy and can inform physicians on their techniques to optimize their practice as well as provide more consistent training to residents.

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.

Extravasation of radiopharmaceuticals: Why report?

In this essay, I wish to discuss extravasation in the context of medical imaging and therapy with radiopharmaceuticals. Central to this discussion are two facts. First, they are easily identified, but the frequency of significant extravasations is unclear because there is no generally accepted definition of such an event. And second, there appears to be few reports of injuries from these events. The central thesis of this essay is that these events should be reported and followed so that agreement can be reached on the definition of a "significant" event which should be classified as a medical event in accordance with US Nuclear Regulatory Commission (NRC) regulations. I will also outline steps that can be taken to reduce the risk of extravasations.

Dose Estimation for Extravasation of 177Lu, 99mTc, and 18F

ABSTRACT

Extravasation is the situation in which a nuclear medicine injection deposits some fraction of its radioactivity into the soft tissue rather than the bloodstream and may result in a large local radiation dose to tissue. An understanding of localized radiation dose from such unexpected events can be an important aspect of clinical radiation protection. The aim of this study was to estimate and assess absorbed radiation dose to localized soft tissue for hypothetical scenarios of radiopharmaceutical extravasation. Specifically, the goal was to understand whether a radiopharmaceutical extravasation could exceed the US Nuclear Regulatory Commission's medical event reporting limit of 0.5 Sv dose equivalent to tissue or levels at which tissue damage would be anticipated (1.0 Sv dose equivalent). We used the GATE Monte Carlo simulation software to calculate self-dose to spherical volumes containing uniformly distributed amounts of common radiopharmaceutical isotopes. Simulated volumes, radioactivity levels, and effective half-lives represented real-world nuclear medicine procedures. Chosen scenarios consisted of 50 mCi and 100 mCi 177Lu within 20 cm3 and 40 cm3 tissue volumes and a 60 min biological clearance half-time (59.6 min effective half-life), 6 mCi and 12 mCi 99mTc within 1 cm3 and 5 cm3 tissue volumes and a 120 min biological clearance half-time (90 min effective half-life), and 3 mCi and 6 mCi 18F within 1 cm3 and 5 cm3 tissue volumes with a 30 min biological clearance half-time (23.6 min effective half-life). We calculated absorbed doses to be between 5.5 Gy and 23.5 Gy for 177Lu, between 0.9 Gy and 12.4 Gy for 99mTc, and between 1.5 Gy and 16.2 Gy for 18F. Radiopharmaceutical extravasations can result in tissue doses that surpass both medical event reporting limits and levels at which deterministic effects are expected. Radiation safety programs should include identification, mitigation, dosimetry, and documentation of significant extravasation events.

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.

177Lu-DOTA-0-Tyr3-octreotate infusion modeling for real-time detection and characterization of extravasation during PRRT

PURPOSE

Given the recent and rapid development of peptide receptor radionuclide therapy (PRRT), increasing emphasis should be placed on the early identification and quantification of therapeutic radiopharmaceutical (thRPM) extravasation during intravenous administration. Herein, we provide an analytical model of 177Lu-DOTA0-Tyr3-octreotate (Lutathera®) infusion for real-time detection and characterization of thRPM extravasation.

METHODS

For 33 Lutathera®-based PRRT procedures using the gravity infusion method, equivalent dose rates (EDRs) were monitored at the patient's arm. Models of flow dynamics for nonextravasated and extravasated infusions were elaborated and compared to experimental data through an equivalent dose rate calibration. Nonextravasated infusion was modeled by assuming constant volume dilution of 177Lu activity concentration in the vial and Poiseuille-like laminar flow through the tubing and patient vein. Extravasated infusions were modeled according to their onset times by considering elliptically shaped extravasation region with different aspect ratios.

RESULTS

Over the 33 procedures, the peak of the median EDR was reached 14 min after the start of the infusion with a value of 450 µSv h-1. On the basis of experimental measurements, 1 mSv h-1 was considered the empirical threshold for Lutathera® extravasation requiring cessation of the infusion and start again with a new route of injection. According to our model, the concentration of extravascular activity was directly related to the time of extravasation onset and its duration, a finding inherent in the gravity infusion method. This result should be considered when planning therapeutic strategy in the case of RPM extravasation because the local absorbed dose for β-emitters is closely linked to activity concentration. For selected EDR values, charts of extravasated activity, volume, and activity concentration were computed for extravasation characterization.

CONCLUSION

We proposed an analytical model of Lutathera® infusion and extravasation (gravity method) based on EDR monitoring. This approach could be useful for the early detection of thRPM extravasation and for the real-time assessment of activity concentration and volume accumulation in the extravascular medium.

Radiopharmaceutical Extravasation: Pragmatic Radiation Protection

ABSTRACT

Inadvertent injection of a radiopharmaceutical agent into a patient's arm tissue instead of into the appropriate blood vessel can cause the injection to infiltrate underlying tissue and produce a potentially substantial, localized irradiation to the patient's arm and skin tissue. When this type of misadministration occurs, called an extravasation, it should be recognized, mitigated, and monitored for patient health and safety. Immediate symptoms of radiopharmaceutical extravasation may include swelling, edema, pain, or numbness in the vicinity of the extravasation site; inflammation; and drainage from the site. Some infiltrations may go unnoticed until later. Pragmatic elements of radiation safety include imaging to assess the geometry, volume, and anatomic distribution of activity, collection of tissue count-rate data over retention times, calibration against known activity levels, and dosimetry to help clinicians determine whether an extravasation is severe and whether the patient should be followed for adverse tissue reactions.

A case report of radiopharmaceutical needlestick injury with scintigraphic imaging and dose quantification

Attention to the implications of common needle stick injuries has focused heavily on the risk of cross-infection from blood-borne pathogens. An additional risk to the nuclear medicine healthcare worker is that of subcutaneous radioactive contamination from radiopharmaceuticals. This case report provides a rare opportunity to examine the clinical and operator causes of one such event during the dispensing of ^99mTc-Tetrofosmin. Contamination monitoring, scintigraphic imaging, and quantification of effective radiation dose provide the level of risk to the operator from the subcutaneous radioactive contamination. Findings demonstrated a very low dose to operator and no deterministic radiobiological effects. Delayed imaging demonstrated negligible biological clearance from the injury site. Implications of the findings for clinical practice are discussed, highlighting the need for a careful and calm approach to radiopharmacy activities.

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.

The Scientific and Clinical Case for Reviewing Diagnostic Radiopharmaceutical Extravasation Long-Standing Assumptions

Background: The patient benefit from a diagnostic nuclear medicine procedure far outweighs the associated radiation risk. This benefit/risk ratio assumes a properly administered radiopharmaceutical. However, a significant diagnostic radiopharmaceutical extravasation can confound the procedure in many ways. We identified three current extravasation hypotheses espoused by medical societies, advisory committees, and hundreds of individual members of the nuclear medicine community: diagnostic extravasations do not cause harm, do not result in high absorbed dose to tissue, and require complex dosimetry methods that are not readily available in nuclear medicine centers. We tested these hypotheses against a framework of current knowledge, recent developments, and original research. We conducted a literature review, searched regulatory databases, examined five clinical cases of extravasated patients, and performed dosimetry on those extravasations to test these globally accepted hypotheses. Results: A literature review found 58 peer-reviewed documents suggesting patient harm. Adverse event/vigilance report database reviews for extravasations were conducted and revealed 38 adverse events which listed diagnostic radiopharmaceutical extravasation as a factor, despite a regulatory exemption for required reporting. In our own case material, assessment of care was evaluated for five extravasated patients who underwent repeat imaging. Findings reflected results of literature review and included mis- or non-identification of lesions, underestimation of Standardized Uptake Values (SUVs) by 19-73%, classification of scans as non-diagnostic, and the need to repeat imaging with the associated additional radiation exposure, inconvenience, or delays in care. Dosimetry was performed for the same five cases of diagnostic radiopharmaceutical extravasation. Absorbed doses to 5 cm3 of tissue were between 1.1 and 8.7 Gy, and shallow dose equivalent for 10 cm2 of skin was as high as 4.2 Sv. Conclusions: Our findings suggest that significant extravasations can or have caused patient harm and can irradiate patients' tissue with doses that exceed medical event reporting limits and deterministic effect thresholds. Therefore, diagnostic radiopharmaceutical injections should be monitored, and dosimetry of extravasated tissue should be performed in certain cases where thresholds are thought to have been exceeded. Process improvement efforts should be implemented to reduce the frequency of extravasation in nuclear medicine.