The study of external dose rate and retained body activity of patients receiving 131I therapy for differentiated thyroid carcinoma

Radiation Safety and External Radiation Exposure Rate of Patients Receiving I-131 Therapy for Hyperthyroidism and Remnant Ablation as Outpatient: An Institutional Experience

Objective  Our objective was to study the radiation exposure rate as function of time in the administration of radioiodine iodine-131 (I-131) for the treatment of thyrotoxicosis or Graves' disease and remnant ablation on an outpatient basis at the Department of Nuclear Medicine, and also, to study the impact of revised discharge criteria for radioiodine therapy enforced by the Atomic Energy Regulatory Board (AERB) of India. Materials and Methods  This study included patients who underwent low-dose radioiodine therapy using I-131. Patients were classified into two different groups, that is, group A and group B. Group A included patients receiving low dose I-131 for the treatment of thyrotoxicosis, whereas group B included patients receiving I-131 therapy for the ablation of residual thyroid tissue after total thyroidectomy. The radiation exposure rate was measured using a radiation detector in milli roentgen per hour (mR/h) at 5 cm distance of stomach and neck levels and with the patient standing at the distance of 1 m after oral administration of I-131 at 0, 1, and 2 hours. Results  A total of 134 (17 males and 117 females) patients were included in the study. Group A comprised 102 (14 male and 88 females) patients and group B of 32 (3 males and 29 females) patients. At the neck level, the average exposure rate in group A versus group B after 0, 1, and 2 hours was observed to be 6.9 versus 22.27 mR/h, 33.67 versus 43.39 mR/h, and 41.75 versus 48.90 mR/h, respectively. At the stomach level, the exposure rate was 23.65 versus 71.32 mR/h, 13.27 versus 48.45 mR/h, and 9.91 versus 39.43 mR/h after 0, 1, and 2 hours, respectively. At a distance of 1 m, the exposure rate was 1.31 versus 2.99 mR/h, 1.05 versus 2.58 mR/h, and 0.92 versus 2.21 mR/h, respectively. Conclusion  Exposure rate measured for patients treated with up to 1,110 MBq (30 mCi) of I-131 was under permissible limits as per revised discharged limits, that is, 50 µSv/h (5 mR/h) prescribed by AERB, India. The patients undergoing radioiodine therapy I-131 (up to 1,110 MBq/30 mCi) can be discharged safely 2 hours postadministration following good work practice along with providing proper radiation safety instructions to patients.

A real-time system to report abnormal events involving staff in a nuclear medicine therapy unit

A system for internal and voluntary reporting of abnormal events in a Nuclear Medicine Therapy Unit is described. This system is based on the Internet of Things and is composed of an application for mobile devices and a wireless network of detectors. The application is addressed to healthcare professionals and is intended to be a user-friendly tool to make the reporting procedure little laborious. The network of detectors allows for a real-time measurement of the dose distribution in the patient's room. The staff was involved in all stages, from the design of the dosimetry system and mobile application up to their final testing. Face-to-face interviews were carried out with 24 operators in different roles in the Unit (radiation protection experts, physicians, physicists, nuclear medicine technicians and nurses). The preliminary results of the interviews and the current state of development of the application and the detection network will be described.

A SIMPLE AND NOVEL APPROACH TO STUDY KINETICS AND ESTIMATE RADIATION DOSES FROM INTERNALLY ADMINISTERED RADIOPHARMACEUTICALS USING AN EXTERNAL DOSE MEASUREMENT SYSTEM

Various methods have been reported to study radiotracer kinetics and make internal dosimetry feasible in the routine clinical nuclear medicine practice. The aim of the present study was to quantify cumulative activity and organ doses using an indigenously designed and fabricated external dose measurement system. The measurement was demonstrated on patients undergoing whole-body (WB) 18F-FDG (Fluorine-18-fluorodeoxyglucose) direct positron emission tomography/computed tomography investigations. An external dose measurement system comprising of an ionisation chamber-survey meter and the movable focussing collimator was used to quantify the uptake of 18F-FDG in liver and brain. Cumulative activity and normalised cumulative activity in these organs were calculated. The results were validated by performing measurements on a phantom uniformly filled with known activity of 18F-FDG.The difference in the absorbed dose estimated with and without collimator was statistically significant (p < 0.05). The external dose measurement technique is relatively novel, convenient and reliable for the assessment of internal absorbed dose of organs.

IPEM topical report: current molecular radiotherapy service provision and guidance on the implications of setting up a dosimetry service

Despite a growth in molecular radiotherapy treatment (MRT) and an increase in interest, centres still rarely perform MRT dosimetry. The aims of this report were to assess the main reasons why centres are not performing MRT dosimetry and provide advice on the resources required to set-up such a service. A survey based in the United Kingdom was developed to establish how many centres provide an MRT dosimetry service and the main reasons why it is not commonly performed. Twenty-eight per cent of the centres who responded to the survey performed some form of dosimetry, with 88% of those centres performing internal dosimetry. The survey showed that a 'lack of clinical evidence', a 'lack of guidelines' and 'not current UK practice' were the largest obstacles to setting up an MRT dosimetry service. More practical considerations, such as 'lack of software' and 'lack of staff training/expertise', were considered to be of lower significance by the respondents. Following on from the survey, this report gives an overview of the current guidelines, and the evidence available demonstrating the benefits of performing MRT dosimetry. The resources required to perform such techniques are detailed with reference to guidelines, training resources and currently available software. It is hoped that the information presented in this report will allow MRT dosimetry to be performed more frequently and in more centres, both in routine clinical practice and in multicentre trials. Such trials are required to harmonise dosimetry techniques between centres, build on the current evidence base, and provide the data necessary to establish the dose-response relationship for MRT.

A Solution for Iterative Determination of Patient Release Instructions for Fractionated Radionuclide Therapy

INTRODUCTION

For fractionated radionuclide therapy protocols that involve large activities administered within short periods of time, there is a lack of guidance concerning how patient release calculations should be performed.

OBJECTIVES

Present a solution for estimating the effective dose of individuals exposed to a patient undergoing fractionated radionuclide therapy; this is intended to be used for iterative determination of patient release instructions.

METHODS

The effective dose of an individual in the vicinity of a patient is described by a piecewise function that is integrated over periods of time that are defined by several variables relevant to clinical planning of fractionated radionuclide therapy protocols. This solution is compared to a simpler calculation that treats all administrations as identical events.

RESULTS

For the two compared methodologies, their equivalence for estimating effective dose depends on several variables. However, for protocols where the elimination time of the radionuclide is far smaller than the time between administrations, both methodologies produce essentially equal results.

CONCLUSION

The author recommends using the presented solution for iterative determination of patient release instructions if a simpler approach generates release instructions that are overly restrictive. Doing so will allow for less strict release instructions because the dose mitigation from repeated adherence to release instructions after each fraction, in addition to potential inpatient time after each fraction, will be taken into account. Lastly, a spreadsheet that incorporates the presented solution has been made freely available for download.

Radioactive Iodine Therapy in Patients with Differentiated Thyroid Cancer: Study of External Dose Rate Attenuation Law and Individualized Patient Management

BACKGROUND

Therapy with radioactive iodine (¹³¹I) is a well established treatment method for postsurgical differentiated thyroid carcinoma (DTC). A fixed discharge time is generally set, regardless of individual differences in residual body radioactivity (RBA). This study aimed to investigate the RBA of each patient to find the attenuation law and to identify underlying factors in order to predict the time point for a safe, scientifically sound discharge plan.

METHODS

A total of 231 DTC patients undergoing ¹³¹I treatment were all treated with 3.7 GBq (100 mCi) of ¹³¹I. RBA was estimated by measuring the external body dose rate (EDR) at a distance of 1 m from the body surface between 0 and 72 hours after oral administration of ¹³¹I. Data from each patient were used to establish a time-EDR value (h-μSv/h) curve. Software was developed to predict the time when a patient's dose equivalent meets the national safety standard by including six time points between 40 and 60 hours. Several factors that might affect that time were analyzed.

RESULTS

The EDR attenuation law in patients could be described with a double exponential decay model, and the cutoff value was set as 23.3 μSv/h, upon which the predictive software was developed. Student's t-test showed there was no statistical difference between predicted values and the actual measured values (p > 0.05). Correlation analysis found that serum thyroglobulin, total triiodothyronine, total thyroxine, free triiodothyronine, free thyroxine, thyrotropin, 2- and 24-hour iodine uptake rate of the thyroid, scores of ^99mTc-pertechnetate thyroid scan, scores of ¹³¹I whole-body scan, scores of ultrasound scan, and gastrointestinal residues were associated with attenuation speed. A further multiple linear regression analysis found that 24-hour iodine uptake (X₁), residual thyroid grading by ¹³¹I whole-body scan (X₂), blood free triiodothyronine (X₃) and free thyroxine (X₄) predominantly influenced the decline of the EDR. The regression equation was Ŷ = 2.091X₁ + 6.370X₂ + 4.529X₃ + 2.466X₄ - 8.614 (F = 44.03, p < 0.01).

CONCLUSIONS

An effective and convenient method was created to measure and predict the individual safety time for discharge. This could play a significant role not only for scientific hospital discharge planning, rational use of medical resources, and better individualized management, but also in public radiation protection.