Use of a dosimetry-based RAI protocol for treatment of benign hyperthyroidism optimises response while minimising exposure to ionising radiation.

BACKGROUND: The optimal treatment strategy for radioiodine (RAI) treatment protocols for benign hyperthyroidism remains elusive. Although individualised activities are recommended in European Law, many centres continue to provide fixed activities. Our institution implemented a dosimetry protocol in 2016 following years of fixed dosing which facilitates the calculation of individualised activities based on thyroid volume and radioiodine uptake. METHODS: This was a retrospective study comparing success rates using a dosimetry protocol targeting an absorbed dose of 150 Gy for Graves' disease (GD) and 125 Gy for Toxic Multinodular Goiter (TMNG) with fixed dosing (200MBq for GD and 400MBq for TMNG) among 204 patients with hyperthyroidism. Success was defined as a non-hyperthyroid state at 1 year for both disease states. Results were analysed for disease specific or patient specific modulators of response. RESULTS: This study included 204 patients; 74% (n = 151) received fixed activities and 26% (n = 53) of activities administered were calculated using dosimetry. A dosimetry-based protocol was successful in 80.5% of patients with GD and 100% of patients with TMNG. Differences in success rates and median activity administered between the fixed (204Mbq) and dosimetry (246MBq) cohort were not statistically significant (p = .64) however 44% of patients with GD and 70% of patients with TMNG received lower activities following treatment with dosimetry as opposed to fixed activities. Use of dosimetry resulted in successful treatment and reduced RAI exposure for 36% of patients with GD, 70% of patients with TMNG, and 44% of patients overall. CONCLUSION: This retrospective clinical study demonstrated that treatment with a dosimetry-based protocol for TMNG and GD achieved comparable success rates to fixed protocols while reducing RAI exposure for over a third of patients with GD and most patients with TMNG. This study also highlighted that RAI can successfully treat hyperthyroidism for some patients with activities lower than commonplace in clinical practise. No patient or disease specific modulators of treatment response were established in this study; however, the data supports a future prospective trial which further scrutinises the individual patient factors governing treatment response to RAI.

Finger doses due to68Ga-labelled pharmaceuticals in PET departments-results of a multi-centre pilot study.

INTRODUCTION: Although the use of68Ga has increased substantially in nuclear medicine over the last decade, there is limited information available on occupational exposure due to68Ga. The purpose of this study is to determine the occupational extremity exposure during the preparation, dispensing and administration of68Ga-labelled radiopharmaceuticals. METHOD: Workers in eight centres wore a ring dosimeter for all tasks involving68Ga-labelled radiopharmaceuticals for a minimum of one month. Additionally, the fingertip dose was monitored in two centres and the hand with the highest ring dose during68Ga procedures was also identified in one centre. RESULTS: The median normalised ring dose for68Ga procedures was found to be 0.25 mSv GBq-1(range 0.01-3.34). The normalised68Ga ring doses recorded in this study are similar to that found in the literature for18F. This study is consistent with previous findings that the highest extremity dose is found on the non-dominant hand. A limited sub study in two of the centres showed a median fingertip to base of the finger dose ratio of 4.3. Based on this median ratio, the extrapolated annual68Ga fingertip dose for 94% of the workers monitored in this study would be below Category B dose limit (150 mSv) and no worker would exceed Category A dose limit (500 mSv). CONCLUSION: When appropriate shielding and radiation protection practices are employed, the extremity dose due to68Ga is comparable to that of18F and is expected to be well below the regulatory limits for the majority of workers.

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.

Review of extremity dosimetry in nuclear medicine.

The exposure of the fingers is one of the major radiation protection concerns in nuclear medicine (NM). The purpose of this paper is to provide an overview of the exposure, dosimetry and protection of the extremities in NM. A wide range of reported finger doses were found in the literature. Historically, the highest finger doses are found at the fingertip in the preparation and dispensing of18F for diagnostic procedures and90Y for therapeutic procedures. Doses can be significantly reduced by following recommendations on source shielding, increasing distance and training. Additionally, important trends contributing to a lower dose to the fingers are the use of automated procedures (especially for positron emission tomography (PET)) and the use of prefilled syringes. On the other hand, the workload of PET procedures has substantially increased during the last ten years. In many cases, the accuracy of dose assessment is limited by the location of the dosimeter at the base of the finger and the maximum dose at the fingertip is underestimated (typical dose ratios between 1.4 and 7). It should also be noted that not all dosimeters are sensitive to low-energy beta particles and there is a risk for underestimation of the finger dose when the detector or its filter is too thick. While substantial information has been published on the most common procedures (using99mTc,18F and90Y), less information is available for more recent applications, such as the use of68Ga for PET imaging. Also, there is a need for continuous awareness with respect to contamination of the fingers, as this factor can contribute substantially to the finger dose.

Gender differences in estimating I-131 thyroid uptake from Tc-99m thyroid uptake for benign thyroid disease.

OBJECTIVE: For radioactive Iodine-131 (131I) treatments of thyroid diseases, increased efficacy has been reported for personalized dosimetry treatments. The measurement of Iodine-131 thyroid uptake (131IU) is required in these cases. This study aims to investigate whether 99mTc thyroid uptake (99mTcU) may be used in place of 131IU for implementing personalised treatments. METHODS: A retrospective study of 152 benign thyroid disease 131I treatments was carried out during 2012-2020; 117 treatments were for female patients while 35 were for male patients diagnosed with either Graves' disease, multinodular goitre or toxic nodules. RESULTS: A statistically significant correlation was found between 131IU and 99mTcU data, with the data more correlated for male than female patients (r = 0.71 vs 0.38, p-value < 0.001). Patient age and time difference between the two respective uptake measurements significantly influenced the uptake correlation in females but not for the male cohort, although there was no significant difference between the parameters across gender. Thyroid diagnosis and hormone levels showed a significant correlation with uptakes in both genders. Estimating 131IU based on 99mTcU was shown to be predictive for male but not in female patients (R2 = 91% vs 16%). CONCLUSION: Estimating 131IU based on 99mTcU is not recommended for females at our centre. Males reported good correlation, but a larger sample would be needed for validation. ADVANCES IN KNOWLEDGE: The initial findings showed a significant gender difference in benign thyroid uptake parameters at our centre, highlighting the potential need for gender consideration when planning 131IU patient management and when reporting studies results.

Multimodal Breast Phantoms for Microwave, Ultrasound, Mammography, Magnetic Resonance and Computed Tomography Imaging.

The aim of this work was to develop multimodal anthropomorphic breast phantoms suitable for evaluating the imaging performance of a recently-introduced Microwave Imaging (MWI) technique in comparison to the established diagnostic imaging modalities of Magnetic Resonance Imaging (MRI), Ultrasound (US), mammography and Computed Tomography (CT). MWI is an emerging technique with significant potential to supplement established imaging techniques to improve diagnostic confidence for breast cancer detection. To date, numerical simulations have been used to assess the different MWI scanning and image reconstruction algorithms in current use, while only a few clinical trials have been conducted. To bridge the gap between the numerical simulation environment and a more realistic diagnostic scenario, anthropomorphic phantoms which mimic breast tissues in terms of their heterogeneity, anatomy, morphology, and mechanical and dielectric characteristics, may be used. Key in this regard is achieving realism in the imaging appearance of the different healthy and pathologic tissue types for each of the modalities, taking into consideration the differing imaging and contrast mechanisms for each modality. Suitable phantoms can thus be used by radiologists to correlate image findings between the emerging MWI technique and the more familiar images generated by the conventional modalities. Two phantoms were developed in this study, representing difficult-to-image and easy-to-image patients: the former contained a complex boundary between the mammary fat and fibroglandular tissues, extracted from real patient MRI datasets, while the latter contained a simpler and less morphologically accurate interface. Both phantoms were otherwise identical, with tissue-mimicking materials (TMMs) developed to mimic skin, subcutaneous fat, fibroglandular tissue, tumor and pectoral muscle. The phantoms' construction used non-toxic materials, and they were inexpensive and relatively easy to manufacture. Both phantoms were scanned using conventional modalities (MRI, US, mammography and CT) and a recently introduced MWI radar detection procedure called in-coherent Multiple Signal Classification (I-MUSIC). Clinically realistic artifact-free images of the anthropomorphic breast phantoms were obtained using the conventional imaging techniques as well as the emerging technique of MWI.

Monitoring Ionizing Radiation Exposure for Cardiotoxic Effects of Breast Cancer Treatment.

Serial assessments of left ventricular ejection fraction (LVEF) are customary in patients with breast cancer receiving trastuzumab. Radionuclide angiography (RNA) is often used; however, a typical monitoring schedule could include 5 scans in a year. We evaluated the proportion of imaging-related ionizing radiation attributable to RNA in 115 patients with breast cancer, from 3 medical centers in the United States, Ireland, and Japan, who completed 12 months of trastuzumab treatment. Estimated radiation dose (ERD) was used to calculate exposure associated with imaging procedures spanning the 18 months before and after trastuzumab therapy. In addition, 20 cardiologists and oncologists from participating centers were surveyed for their opinions regarding the contribution of RNA to overall radiation exposure during trastuzumab treatment. When RNA was used to monitor LVEF, the mean ERD from imaging was substantial (34 ± 24.3 mSv), with the majority attributable solely to RNA (24.7 ± 14.8 mSv, 72.6%). Actual ERD associated with RNA in this population differed significantly from the perception in surveyed cardiologists and oncologists; 70% of respondents believed that RNA typically accounted for 0% to 20% of overall radiation exposure from imaging; RNA actually accounted for more than 70% of ERD. In conclusion, RNA was used to monitor LVEF in most patients in this cohort during and after trastuzumab therapy. This significantly increased ERD and accounted for a greater proportion of radiation than that perceived by surveyed physicians. ERD should be taken into account when choosing a method of LVEF surveillance. Alternative techniques that do not use radiation should be strongly considered.

Langevin equation approach to diffusion magnetic resonance imaging.

The normal phase diffusion problem in magnetic resonance imaging (MRI) is treated by means of the Langevin equation for the phase variable using only the properties of the characteristic function of Gaussian random variables. The calculation may be simply extended to anomalous diffusion using a fractional generalization of the Langevin equation proposed by Lutz [E. Lutz, Phys. Rev. E 64, 051106 (2001)] pertaining to the fractional Brownian motion of a free particle coupled to a fractal heat bath. The results compare favorably with diffusion-weighted experiments acquired in human neuronal tissue using a 3 T MRI scanner.

An interactive taxonomy of MR imaging sequences.

Discerning an underlying structure in the array of magnetic resonance (MR) imaging sequences and acronyms available is a bewildering task. Attempts have been made to present standard taxonomies of MR imaging sequences, primarily on the basis of their underlying physics. Despite this, it is difficult to usefully incorporate given taxonomies into routine clinical knowledge. The links, differences, and similarities among sequences are multidimensional and too complex for tabular presentation on the printed page. The authors present an interactive taxonomy of MR imaging sequences. With this graphical interface, the user can explore the changing relationships among a wide range of sequence types as they are viewed from different perspectives and through different associations, working through a natural learning process.