Measuring the actual I-131 thyroid uptake curve with a collar detector system: a feasibility study

Should we reconsider blocking the thyroid for 123 I-Ioflupane studies in elderly patients: quantifying radiation dose to the unblocked thyroid and implications for clinical practice

OBJECTIVES

To measure the absorbed dose to the thyroid in patients injected with 123 I-Ioflupane where the thyroid was not blocked with prophylaxis to investigate whether thyroid blocking should be limited to younger patients. This risk from the additional absorbed dose to the thyroid was then compared to the risk from iodine overdose through ingestion of the iodide prophylaxis, resulting in iodine-induced hyper/hypothyroidism (IIH).

METHODS

A cohort of patients (n = 30) who did not receive thyroid prophylaxis underwent static thyroid imaging 3 h after 123 I-Ioflupane administration. The measured thyroidal uptake of free 123 I was then extrapolated to peak uptake time (24 h post-administration). This value was used to calculate cumulated activity in the thyroid and thus thyroid-thyroid absorbed dose D(rthy←rthy ) using the relevant S-value in the MIRD method.

RESULTS

Mean D(rthy←rthy ) was found to be 13.6 mGy with an SD of 8.8 mGy; this would contribute an additional 0.5 mSv to the effective dose.

CONCLUSION

ARSAC recommends in its Notes for Guidance prophylactic thyroid blocking if the absorbed dose to the thyroid is >50 mGy; the maximum thyroid dose in this study cohort was 36.3 mGy. With risk from IIH and its associated cardiac complications increasing with age, this study suggests that iodide prophylaxis with 123 I-Ioflupane should be reconsidered for elderly patient.

Evolution of Portable Sensors for In-Vivo Dose and Time-Activity Curve Monitoring as Tools for Personalized Dosimetry in Molecular Radiotherapy

Treatment personalization in Molecular Radiotherapy (MRT) relies on pre- and post-treatment SPECT/ PET-based images and measurements to obtain a patient-specific absorbed dose-rate distribution map and its evolution over time. Unfortunately, the number of time points that are available per patient to investigate individual pharmacokinetics is often reduced by limited patient compliance or SPECT or PET/CT scanner availability for dosimetry in busy departments. The adoption of portable sensors for in-vivo dose monitoring during the entire treatment could improve the assessment of individual biokinetics in MRT and, thus, the treatment personalization. The evolution of portable devices, non-SPECT/PET-based options, already used for monitoring radionuclide activity transit and accumulation during therapy with radionuclides (i.e., MRT or brachytherapy), is presented to identify valuable ones, which combined with conventional nuclear medicine imaging systems could be effective in MRT. External probes, integration dosimeters and active detecting systems were included in the study. The devices and their technology, the range of applications, the features and limitations are discussed. Our overview of the available technologies encourages research and development of portable devices and dedicated algorithms for MRT patient-specific biokinetics study. This would represent a crucial advancement towards personalized treatment in MRT.

Investigation of the Suitability of a Commercial Radiation Sensor for Pretherapy Dosimetry of Radioiodine Treatment Patients

Radioiodine (I-131) therapy is routinely used to treat conditions of the thyroid. Dosimetry planning in advance of I-131 therapy has been shown to improve patient treatment outcomes. However, this pretherapy dosimetry step requires multiple outpatient appointments and is not feasible for patients living at greater distances. Here, the feasibility of a commercially available smartphone-operated radiation sensor (Smart Geiger Pro, Technonia) for at-home patient pretherapy dosimetry has been investigated. The influence of both treatment-specific parameters (radioisotope activity, gamma photon energy, patient size) and external factors (sensor placement and motion) on the ability of the radiation sensor to accurately quantify radiation dose rates has been studied. The performance limits of the radiation sensor have been identified. A preliminary trial of the sensor on four I-131 patients prior to their therapy, conducted at the Nuclear Medicine/Endocrinology departments of St James's Hospital Dublin, is also presented. A comparable performance between the low-cost radiation sensor and that of a hospital-grade thyroid uptake probe is reported. This work demonstrates the potential of low-cost commercially available radiation sensors as a solution for at-home pretherapy dosimetry for long distance patients, or indeed for hospitals who wish to implement dosimetry at reduced cost. Recommended conditions for optimum sensor performance use are presented.

Real-time quantitation of thyroidal radioiodine uptake in thyroid disease with monitoring by a collar detection device

Radioactive iodine (RAI) is safe and effective in most patients with hyperthyroidism but not all individuals are cured by the first dose, and most develop post-RAI hypothyroidism. Postoperative RAI therapy for remnant ablation is successful in 80–90% of thyroid cancer patients and sometimes induces remission of nonresectable cervical and/or distant metastatic disease but the effective tumor dose is usually not precisely known and must be moderated to avoid short- and long-term adverse effects on other tissues. The Collar Therapy Indicator (COTI) is a radiation detection device embedded in a cloth collar secured around the patient’s neck and connected to a recording and data transmission box. In previously published experience, the data can be collected at multiple time points, reflecting local cervical RAI exposure and correlating well with conventional methods. We evaluated the real-time uptake of RAI in patients with hyperthyroid Graves’ disease and thyroid cancer. We performed a pilot feasibility prospective study. Data were analyzed using R^© (version 4.0.3, The R Foundation for Statistical Computing, 2020), and Python (version 3.6, Matplotlib version 3.0.3). The COTI was able to provide a quantitative temporal pattern of uptake within the thyroid in persons with Graves’ disease and lateralized the remnant tissue in persons with thyroid cancer. The study has demonstrated that the portable collar radiation detection device outside of a healthcare facility is accurate and feasible for use after administration of RAI for diagnostic studies and therapy to provide a complete collection of fractional target radioactivity data compared to that traditionally acquired with clinic-based measurements at one or two time-points.

Clinical Trials Registration NCT03517579, DOR 5/7/2018.

Dependency of the remnant 131I-NaI biokinetics on the administered activity in patients with differentiated thyroid cancer

PURPOSE

To study the dependency of the effective half-life on the administered activity and the correlation between the time-integrated activity and the remnant uptake at 2d and 7d in patients treated for DTC with 1.11 GBq, 3.7 GBq or 5.55 GBq of ¹³¹I-NaI.

METHODS

Ninety-two patients undergoing total thyroidectomy and lymph node removal were included. If cancer had not spread to lymph nodes, patients received 1.11 GBq of ¹³¹I-NaI when the lesion maximal diameter was smaller than 4 cm, and 3.7 GBq for bigger sizes. If cancer had spread to lymph nodes patients received 5.55 GBq. There were 30, 49 and 13 patients respectively treated with 1.11 GBq(Group 1), 3.7 GBq(Group 2) and 5.55 GBq(Group 3). Two SPECT/CT scans were performed at 2d and 7d after radioiodine administration for each patient to determine the thyroid remnant activities and effective half-lives of the radioiodine.

RESULTS

Statistical analysis showed significant differences (p < 0.05) in the effective half-life among patients treated with 1.11 GBq, 3.7 GBq and 5.55 GBq. A high positive correlation (ρ > 0.95) was found between the time-integrated activity and the remnant activity at 2d for the three groups of patients.

CONCLUSIONS

There were significant differences in the effective half-life of the radioiodine in remnants of patients treated with activities of 1.11 GBq, 3.7 GBq or 5.55 GBq. The high positive linear correlation found between the time-integrated activity and the remnant activity at 2d for the three groups of patients indicate that the time-integrated activity could be estimated from one time-point.

Thyroid uptake test with portable device (COTI) after 131I tracer administration: proof of concept

COTI (collar therapy indicator) has been recently introduced for the detection of gamma rays with emphasis on thyroid investigations. The aim of this study was to test the feasibility of a prototype version of COTI including activity detectors with low sensitivity in performing thyroid uptake measurements for a large group of patients. Consequently, thyroid uptake tests were carried out for a total of 89 patients (22 males and 67 females; age: 44 ± 13 years) with thyroid cancer (n = 74), hyperthyroidism (n = 16) at 2 and 24 h after administration of 0.44-2 MBq of ¹³¹I. Eight individuals among the thyroid cancer patients were monitored up to 96 h after administration. The COTI device was equipped with two CsI (Tl) detectors, known as LoHi type, sensitive to activity ranges from 0.02 to 30 MBq of ¹³¹I. The uptake values from COTI were compared with those measured with a standard probe. It was found that the mean uptake of thyroid activity in thyroid cancer patients was 2.1 ± 1.3% at 2 h when measured with the standard probe, while it was 2.2 ± 1.2% when measured with COTI. In addition, the average uptake at 24 h after administration was 2.5 ± 3.2% and 3.2 ± 3.8% measured with COTI and the standard probe, respectively. A strong correlation was found at 24 h between the results obtained with COTI and the standard probe, while a weaker correlation was seen at 2 h. Overall, there was no significant difference between the results obtained with the standard probe and those obtained with COTI at both 2 and 24 h (P_value ≥ 0.05). Besides, 85% of the uptake values measured with COTI were less than those measured with the standard probe at the 24 h after administration. The average uptake value was 0.9 ± 0.8% after 96 h by COTI, and 1.4 ± 1.3% by the standard probe. Pertaining to the hyperthyroidism patients, COTI showed mean uptake values of 20 ± 16% and 23 ± 18% at 2 and 24 h, respectively. In contrast, the standard probe suggested higher mean uptake values of 26 ± 18% and 30 ± 22%, respectively. It is concluded that the prototype of COTI used in the present study has been proved to be a feasible and promising tool in thyroid investigations. It is noted, however, that the next COTI generation should include detectors equipped with collimator and energy discrimination.

In vitro evaluation of an iodine radionuclide dosimeter (IRD) for continuous patient monitoring

In vivo dosimetry of the patients treated by I-131 is important from patient dosimetry and radiation protection points of view. Knowledge of delivered dose to the target volume and adjacent normal tissues can improve the effectiveness of radioiodine treatment. Herein, design, fabrication, and assessment processes of an iodine radionuclide dosimeter (IRD) are explained. Two CsI(Tl) scintillator crystals coupled to photodiodes were used in IRD fabrication with specifications derived from Monte Carlo (MC) simulation. Linearity, sensitivity, and long-term performance of the system were tested. Delivered dose due to a known administered activity of I-131 was calculated by MC simulation which was validated based on the Medical Internal Radiation Dose (MIRD) Committee formalism, and the calibration factor was provided. Using the current mode signal acquisition method, the system showed a linear response up to 8.2 GBq radioiodine activity to prohibit the pile-up error without a need for correction factor. On the other hand, IRD was sensitive down to the rarely detectable activity of 7.4 MBq. A prototype version of the IRD system has been developed to guide the hospital staff for the safe release of iodine - administered patients and to provide an insight for physicians about the delivered dose to the thyroid and nearby organs. Graphical abstract IRD attached to MIHAN.