The 2020 national diagnostic reference levels for nuclear medicine in Japan

Radiation Exposure with Self-Expandable Metallic Stent versus Transanal Decompression Tube for Malignant Colorectal Obstruction: A Post Hoc Propensity Score Matched Analysis

Background: Although several reports have compared the outcomes of self-expandable metallic stent (SEMSs) and transanal decompression tube (TDT) placement for malignant colorectal obstruction (MCO), few studies have compared the radiation exposure (RE) associated with these two procedures. Consequently, we aimed to compare the RE of SEMS and TDT placements for MCO using propensity score matching (PSM) in a multi-center, prospective observational study. Methods: This study investigated the clinical data of 236 patients who underwent SEMS or TDT placement. The air kerma at the patient entrance reference point (Ka,r: mGy) and air kerma-area product (PKA; Gycm2) were measured and compared between SEMS and TDT groups after PSM. Results: After PSM, 61 patients were identified in each group. The median Ka,r in the SEMS group was significantly greater than that in the TDT group (77.4 vs. 55.6 mGy; p = 0.025) across the entire cohort. With respect to subgroup analyses by location, in the rectum, the median Ka, r and PKA were significantly greater in the SEMS group than in the TDT group (172.9 vs. 34.6 mGy; p = 0.001; and 46.0 vs. 18.1 Gycm2; p = 0.006, respectively). However, in the colon, the RE parameters did not significantly differ between the two groups. Conclusions: TDT might be a more suitable option for decompression in patients with malignant rectal obstruction due to its lower RE and technical advantages. Conversely, SEMS placement is recommended as the first decompression method to treat malignant colonic obstruction, in line with the current guidelines.

Evaluation of patients' radiation doses and establishment of institutional diagnostic reference levels in nuclear medicine in Oman

This study aimed to develop diagnostic reference levels (DRLs) in Single Photon Emission Computed Tomography/Computed Tomography (SPECT/CT) and Positron Emission Tomography/Computed Tomography (PET/CT) imaging for the most frequent SPECT/CT and PET/CT examinations performed at our institution. A total of 1134 adult patients, who have undergone SPECT/CT and PET/CT scanning over a period of 4 years (2018-2021), were included. The scans consisted of 401 PET/CT and 733 SPECT/CT scans. The CT dosimetry data [CT-dose-index (CTDIvol), dose-length-product (DLP)] and administered activities were collected. The DRLs were calculated for CTDIvol, DLP and administrated activity. The estimated DRLs are given as [median CTDIvol (mGy):median DLP (mGy.cm):median administrated activity (MBq)]: whole body PET/CT: 1.88:175:259; brain PET/CT: 12.9:300:239; cardiac PET/CT: 1.34:32:368; bone SPECT/CT: 2.68:116:763; MPI SPECT/CT (stress-rest): 1.49:52:751-721; parathyroid SPECT/CT: 3.1:126:779; thyroid uptake SPECT: 3.52:147:195; thyroid post-ablation SPECT/CT: 3.85:160:NA. The derived DRLs have allowed careful monitoring of doses delivered to patients and could act as a trigger to investigate doses that systematically exceeds the derived DRLs.

Diagnostic Reference Levels in PET Imaging at Chulabhorn Hospital, Thailand

Diagnostic reference levels (DRLs) are an important tool for controlling radiation exposure and ensuring safety in medical applications. In Thailand, DRL data have been gathered and established for nuclear medicine diagnostics since 2021. However, there is a lack of information on PET imaging examinations. At the National Cyclotron and PET Scan Centre, Chulabhorn Hospital, radiopharmaceuticals are produced for medical imaging and research, and a wide range of PET/CT and PET/MRI examinations are performed. Our objective was to investigate the administered activity of radiopharmaceuticals in patients undergoing PET imaging, especially the existing data on DRLs in medical diagnostic imaging. Methods: This was a retrospective study on nuclear medicine patients at the National Cyclotron and PET Scan Centre in 2023. Statistical analysis, including the mean and the 75th percentile values, was conducted to determine DRLs according to the International Commission on Radiological Protection guidelines. Results: The center performed 8,711 PET/CT and PET/MRI studies with 13 protocols in 2023. The most commonly administered activity was 18F-FDG in oncology and neurology examinations, with DRLs of 186.11 and 136.16 MBq, respectively. These values were notably almost twice lower than several reports in other countries. Conclusion: There is a lack of comprehensive data on most DRLs for PET imaging at this center because of the nonwidespread use of several radiopharmaceuticals. However, the lower DRLs for 18F-FDG can highlight the need for ongoing investigation toward the establishment of local DRLs, as well as assurance on the safety and efficiency of radiation used in nuclear medicine.

Evaluation of X-ray protective goggles in mitigating eye lens radiation exposure during radiopharmaceutical handling and patient care in nuclear medicine

The aim of this study is to estimate eye lens exposure dose when handling radiopharmaceuticals and interacting with patients receiving radiopharmaceuticals, and to verify the usefulness of X-ray protective goggles in mitigating such radiation exposure using phantoms. To evaluate radiation exposure during the handling of radiopharmaceuticals, we employed a fluorescent glass dosimeter to measure the radiation doses associated with 99mTc, 123I, 131I, 111In, and 18F at distances of 30 cm and 60 cm, followed by calculation of the 3 mm dose equivalent rate (3DER). We then estimated the dose reduction rates for various scenarios, including the use of syringe shields and X-ray protective goggles with lead equivalences of 0.07, 0.15, 0.75, and 0.88 mmPb, as well as their combined application. X-ray protective goggles with lead equivalence of 0.75 mmPb outperformed those with 0.07 mmPb and 0.15 mmPb, for all radionuclides and at both source distances. X-ray protective goggles with 0.88 mmPb outperformed those with 0.75 mmPb during handling of 131I and 111In at a distance of 30 cm. In the remaining scenarios, X-ray protective goggles with 0.88 mmPb resulted in marginal reductions or no discernible additional effects. The overall shielding effect of X-ray protective goggles was less pronounced for 131I and 18F, but the combined use of a syringe shield with X-ray protective goggles with 0.75 or 0.88 mmPb improved the dose reduction rate for all scenarios. In simulating patient care, X-ray protective goggles with 0.88 mmPb demonstrated a dose reduction effect of approximately 50% or more. X-ray protective goggles could reduce the 3DER for the eye lens, and were more effective when combined with a syringe shield. It is valid to use a lead equivalence of 0.88 mmPb to fully harness the protective capabilities of X-ray shielding goggles when dealing with all five types of nuclides in clinical settings.

Establishment of National Diagnostic Reference Levels for Administered Activity in Diagnostic Nuclear Medicine in Thailand

The diagnostic reference level (DRL) is a patient-exposure optimization tool used to evaluate radiation doses in medical imaging and provide guidance for protection from them. In Thailand, nuclear medicine DRLs have not been established yet. Therefore, this study surveyed dose levels in routine nuclear medicine procedures to provide national DRLs (NDRLs). Methods: NDRLs in Thailand were established by investigating the administered activity of radiopharmaceuticals in nuclear medicine examination studies. The NDRLs were determined on the basis of the 75th percentile (third quartile) of administered activity distribution as recommended by the International Commission on Radiological Protection. As part of a nationwide survey, datasets for the period between June 1, 2018, and August 31, 2019, were collected from 21 Thailand hospitals with nuclear medicine equipment. All hospitals were asked to report the nuclear medicine imaging devices in use, the standard protocol parameters for selected examinations, the injected activities, and the ages and weights of patients. All data were calculated to determine Thailand NDRLs, which were compared with international NDRLs. Results: The data reported by the 21 hospitals consisted of 4,641 examinations with SPECT or SPECT/CT for general nuclear medicine and 409 examinations with PET. The most widely performed examinations for SPECT were bone, thyroid, oncology, and cardiovascular imaging. The NDRLs for SPECT or SPECT/CT agreed well with published NDRLs for Europe, the United States, Japan, Korea, Kuwait, and Australia. In contrast, the NDRLs for 18F-FDG PET in oncology studies were higher than for Japan, Korea, Kuwait, and Australia but lower than for the United States, the United Kingdom, and the European Union. Conclusion: This study presents NDRL results for adults in Thailand as a way to optimize radiation protection in nuclear medicine imaging. Moreover, the reported injected activity levels were comparable to those of other countries.

Establishment and utilisation of national diagnostic reference level for adult computed tomography examinations in Ghana

The International Atomic Energy Agency, as part of the new regional project (RAF/9/059), recommend the establishment of diagnostic reference levels (DRLs) in Africa. In response to this recommendation, this project was designed to establish and utilise national DRLs of routine computed tomography (CT) examinations. These were done by estimating CT dose index and dose length product (DLP) from a minimum of 20 patient dose report of the most frequently used procedures using 75th percentile distribution of the median values. In all, 22 centres that formed 54% of all CT equipment in the country took part in this study. Additionally, a total of 2156 adult patients dose report were randomly selected, with a percentage distribution of 60, 12, 21 and 7% for head, chest, abdomen-pelvis and lumber spine, respectively. The established DRL for volume CT dose index were 60.0, 15.7, 20.5 and 23.8 mGy for head, chest, abdomen-pelvis and lumber spine, respectively. While the established DRL for DLP were 962.9, 1102.8, 1393.5 and 824.6 mGy-cm for head, chest, abdomen-pelvis, and lumber spine, respectively. These preliminary results were comparable with data from 16 other African countries, European Commission and the International Commission on Radiological Protection. Hence, this study would serve as a baseline for the establishment of a more generalised regional and national adult DRLs for Africa and other developing countries.

National and local diagnostic reference levels for adult18F-FDG and CT in Jordanian PET/CT: findings and implications in practice

This study aims to report the findings of Jordanian national diagnostic reference level (NDRL) survey for fluorodeoxyglucose (18F-FDG) and local diagnostic reference level (LDRL) of computed tomography (CT) used for attenuation correction and anatomical localisation (AC-AL); and AC and diagnostic CT (AC-DX) within the context of whole-body WB and half-body HB adult oncology PET/CT scanning. Two-structured questionnaires were prepared to gather the necessary information: dosimetry data, patient demographics, equipment specification, and acquisition protocols for identified18F-FDG PET/CT procedures. The NDRL and achievable dose were reported based on the 75th and 50th percentiles for18F-FDG administered activity (AA), respectively. The LDRL was reported based on the 50th percentile for (CTDIvol) and (DLP). Data from 562 patients from four Jordanian PET/CT centres were collected. The survey revealed that Jordanian NDRL for AA (303 MBq) was within the acceptable range compared to the published-peer NDRL data (240-590 MBq). However, the18F-FDG AA varied across the participated PET/CT centres. The reported LDRL CTDIvoland DLP of CT used for (AC-AL) was 4.3 mGy and 459.3 mGy.cm for HB CT scan range, and 4.1 mGy and 659.9 mGy.cm for WB CT scans. The reported LDRL for CTDIvoland DLP for HB CT was higher when compared with the United Kingdom (3.2 mGy and 310 mGy.cm). Concurrently, in the context of WB CT, the reported values (i.e. CTDIvol and DLP) were also higher than both Kuwait (3.6 mGy and 659 mGy.cm) and Slovenia (3.6 mGy and 676 mGy.cm). The reported HB CT(AC-DX) was higher than Nordic, New Zealand and Swiss NDRLs and for WB (AC-DX) CT it was higher than Swiss NDRLs. This study reported the first Jordanian NDRL for18F-FDG and LDRL for HB and WB CT associated with18F-FDG PET/CT scans. This data is useful for Jordanian PET/CT centres to compare their LDRL to the suggested DRLs and utilise it in the process of optimising CT radiation doses.

Administered dosage and effective dose estimated from 81Rb-rubidium hydroxide for lung ventilation scintigraphy using 81mKr noble gas

The aim of this study was to estimate the administered dosage of 81mKr noble gas as calculated by the radioactivity of 81Rb-rubidium hydroxide (81RbOH). The administered dosage was regarded as the total amount of 81mKr noble gas. The radioactivity of 81mKr was calculated using the radioactivity of 81RbOH at the examination, the beginning of inhalation, the inhalation duration and the attenuation volume from the generator to the patient for 81mKr noble gas. In addition, we created an Internet survey and asked National University Hospital in Japan to respond to questions regarding the parameters of concern. Survey responses were provided by 38 hospitals (response rate was 90.5%). Twenty-seven hospitals (64.3%) examined lung ventilation scintigraphy using 81mKr noble gas. The mean administered dosage and the effective dose of lung ventilation scintigraphy using 81mKr noble gas were 35.8 ± 22.1 GBq and 0.97 ± 0.60 mSv, respectively.

Enhancing Nuclear Medicine Practice in Saudi Arabia: Advocating for Comprehensive Guidelines and Local Diagnostic Reference Levels

INTRODUCTION

 Diagnostic reference levels (DRLs) were initially introduced by the International Commission on Radiation Protection (ICRP). It refers to the measured quantity of administered activity (MBq) in nuclear medicine imaging studies and is a type of investigation level. DRL is recommended to prevent excessive radiation exposure to patients while maintaining adequate image quality. It should not be implemented as a dose constraint or dose limit. The Saudi Food and Drug Authority (SFDA) is the primary government body responsible for reporting national diagnostic reference levels (NDRLs) for diagnostic medical imaging technologies in Saudi Arabia. Only NDRLs for computed tomography, general X-ray, and mammography have been published and enforced locally. This study aims to establish local DRLs for nuclear medicine imaging procedures at King Abdulaziz University Hospital, Saudi Arabia, preparing for compliance proof once required by local authorities.

METHOD

 Data were collected from all machines, and six common protocols were studied, with data from 50 patients of standard body size for each identified protocol. The study was conducted retrospectively, and the 50th percentile was then calculated for each scan.

RESULTS

Both protocols for renal scans administered the lowest doses to patients (130 MBq and 148 MBq), respectively. The highest dose administered to patients was found to be in bone scans (1110 MBq).

CONCLUSION

The study establishes local DRLs for nuclear medicine imaging in our institution. Median activity dosages in renal, thyroid, and parathyroid imaging were comparable to locally and internationally published DRLs. However, they are higher in cardiac and bone imaging compared to local Saudi DRL and DRL in the European Union and the USA, likely due to the adopted protocols. These highlight the need for modifying the protocols to fulfill optimization efforts. These findings serve as a foundation for compliance with future regulatory requirements, ensuring patient safety and maintaining imaging quality in Saudi healthcare.

Establishment of diagnostic reference levels in computed tomography in two large hospitals in Oman

This study aimed to estimate diagnostic reference levels (DRLs) for the most frequent computed tomography (CT) imaging examinations to monitor and better control radiation doses delivered to patients. Seven CT imaging examinations: Head, Chest, Chest High Resolution (CHR), Abdomen Pelvis (AP), Chest Abdomen Pelvis (CAP), Kidneys Ureters Bladder (KUB) and Cardiac, were considered. CT dosimetric quantities and patient demographics were collected from data storage systems. Local typical values for DRLs were calculated for CTDIvol (mGy), dose length product (DLP) (mGy·cm) and effective doses (mSv) were estimated for each examination. The calculated DRLs were given as (median CTDIvol (mGy):median DLP (mGy·cm)): Head: 39:657; Chest: 13:451; CHR: 6:228; AP: 12:578; CAP: 20:807; KUB: 7:315, and Cardiac: 2:31. Estimated effective doses for Head, Chest, CHR, AP, CAP, KUB and Cardiac were 1.3, 12.7, 6.3, 12.5, 18.1, 5.8 and 0.8 mSv, respectively. The estimated DRLs will act as guidance doses to prevent systematic excess of patient doses.

Interference of cardiac implantable electronic devices and computed tomography imaging in the current era with a phantom model

Introduction

Cardiac implantable electronic devices are used in patients with cardiac rhythm disorders. Computed tomography irradiation is not prohibited for patients with cardiac implantable electronic devices, despite adverse events being reported. Hence, appropriate preparation and knowledge are required before computed tomography irradiation can be carried out in these patients. Since there is limited knowledge or literature about the influence of computed tomography irradiation in cases with recent cardiac implantable electronic devices, we aimed to evaluate the adverse events and elucidate the necessary and sufficient safety measures associated with this therapy.

Methods and Results

We placed cardiac implantable electronic devices on an anthropomorphic phantom model and observed their electrical activity in electrograms, while various protocols of computed tomography irradiation were implemented and adverse events evaluated. Oversensing with pauses of up to 3.2 s was observed in standard computed tomography protocols, but ventricular tachyarrhythmia or other clinically significant events could not be confirmed. Oversensing with pauses of up to 8.0 s was observed and ventricular tachyarrhythmia was detected in the maximum-dose protocols. However, treatments such as antitachycardia pacing or shock therapy for ventricular tachyarrhythmia were not observed because of their absence.

Conclusion

Computed tomography irradiation for patients using cardiac implantable electronic devices is highly unlikely to cause clinically significant adverse events with the device settings and computed tomography protocols currently being used. Changing or monitoring the device settings routinely before computed tomography irradiation is not necessarily required for most patients.

The establishment of national diagnostic reference levels for adult SPECT-CT in Saudi Arabia

This study aims to introduce national diagnostic reference levels (NDRLs) for adult hybrid single photon emission computed tomography (SPECT-CT) in nuclear medicine (NM) departments in the Kingdom of Saudi Arabia. The administered activity (AA) of radiopharmaceuticals, volume-weighted computed tomography dose index (CTDIvol) and dose length product (DLP) for ten hybrid SPECT/CT examinations were collected and analysed for one year. The median of AA, CTDIvoland DLP for each dose quantity was derived and the suggested national DRLs were determined based on the 75thpercentile for all identified SPECT-CT examinations. A comparison of the defined adult NDRLs in Saudi Arabia with the published data of other countries was performed. Although there are no significant variations of the proposed NDRL of AA between countries, the proposed NDRLs of the integrated CT metrics exceed the published data in most procedures. NM departments are urged to consider optimisation for both image quality and radiation protection.

A systematic review and meta-analysis on the radiation dose of computed tomography in hybrid nuclear medicine imaging

BACKGROUND

While diagnostic reference levels (DRLs) are well-established for the radiopharmaceutical part, published DRLs for the CT component of positron emission tomography/computed tomography (PET/CT) and single photon emission computed tomography/computed tomography (SPECT/CT) are limited. This systematic review and meta-analysis provides an overview of the different objectives of CT in hybrid imaging and summarizes reported CT dose values for the most common PET/CT and SPECT/CT examinations. Also, an overview of already proposed national DRLs is given.

METHODS

A systematic literature search was performed to identify original articles reporting CT dose index volume (CTDIvol), dose-length product (DLP) and/or national DRLs for the most frequently performed PET/CT and/or SPECT/CT examinations. Data were grouped according to the clinical objective: diagnostic (D-CT), anatomical localisation (AL-CT) or attenuation correction (AC-CT) CT. Random-effects meta-analyses were conducted.

RESULTS

Twenty-seven articles were identified of which twelve reported national DRLs. For brain and tumour PET/CT imaging, CTDIvol and DLP values were higher for a D-CT (brain: 26.7 mGy, 483 mGy cm; tumour: 8.8 mGy, 697 mGy cm) than for an AC/AL-CT (brain: 11.3 mGy, 216 mGy cm; tumour: 4.3 mGy, 419 mGy cm). Similar conclusions were found for bone and parathyroid SPECT/CT studies: D-CT (bone: 6.5 mGy, 339 mGy cm; parathyroid: 15.1 mGy, 347 mGy cm) results in higher doses than AL-CT (bone: 3.8 mGy, 156 mGy cm; parathyroid: 4.9 mGy, 166 mGy cm). For cardiac (AC-CT), mIBG/octreotide, thyroid and post-thyroid ablation (AC/AL-CT) SPECT/CT pooled mean CTDIvol (DLP) values were 1.8 mGy (33 mGy cm), 4.6 mGy (208 mGy cm), 3.1 mGy (105 mGy cm) and 4.6 mGy (145 mGy cm), respectively. For all examinations, high variability in nuclear medicine practice was observed.

CONCLUSION

The large variation in CT dose values and national DRLs highlights the need for optimisation in hybrid imaging and justifies the clinical implementation for nuclear medicine specific DRLs.

National Diagnostic Reference Levels for Nuclear Medicine in Qatar

Nuclear medicine (NM) started in Qatar in the mid-1980s with a 1-head γ-camera in Hamad General Hospital. However, Qatar is expanding, and now Hamad Medical Corp. has 2 NM departments and 1 PET/CT Center for Diagnosis and Research, with several hybrid SPECT/CT and PET/CT cameras. Furthermore, 2 new NM departments will be established in Qatar in the coming 3 y. Therefore, there is a need to optimize radiation protection in NM imaging and establish diagnostic reference levels (DRLs) for the first time in Qatar. This need is not only for the NM part of the examination but also for the CT part, especially in hybrid SPECT/CT and PET/CT. Methods: Data for adult patients were collected from the 3 SPECT/CT machines in the 2 NM facilities and from the 2 PET/CT machines in the PET/CT center. The 75th percentile values (also known as the third quartile) were considered preliminary DRLs and were consistent with the most commonly administered activities. The results for various general NM protocols were described, especially ^99mTc-based radiopharmaceuticals and PET/CT protocols including mainly oncologic applications. Results: The first DRLs for NM imaging in Qatar adults were established. The values agreed with other published DRLs, as was the case, for example, for PET oncology using ¹⁸F-FDG, with DRLs of 258, 230, 370, 400, and 461-710 MBq for Qatar, Kuwait, Korea, the United Kingdom, and the United States, respectively. Similarly, for cardiac stress or rest myocardial perfusion imaging using ^99mTc-methoxyisobutylisonitrile, the DRLs were 926, 976, 1,110, 800, and 945-1,402 MBq for Qatar, Kuwait, Korea, the United Kingdom, and the United States, respectively. Conclusion: The optimization of administered activity that this study will enable for NM procedures in Qatar will be of great value, especially for new departments that adhere to these DRLs.

Assessment of patients radiation doses associated with computed tomography coronary angiography

Computed tomography coronary angiography (CTCA) has generated tremendous interest over the past 20 years by using multidetector computed tomography (MDCT) because of its high diagnostic accuracy and efficacy in assessing patients with coronary artery disease. This technique is related to high radiation doses, which has raised serious concerns in the literature. Effective dose (E, mSv) may be a single parameter meant to reflect the relative risk from radiation exposure. Therefore, it is necessary to calculate this quantity to point to relative radiation risk. The objectives of this study are to evaluate patients' exposure during diagnostic CCTA procedures and to estimate the risks. Seven hundred ninety patients were estimated during three successive years. The patient's exposure was estimated based on a CT device's delivered radiation dose (Siemens Somatom Sensation 64 (64-MDCT)). The participating physicians obtained the parameters relevant to the radiation dose from the scan protocol generated by the CT system after each CCTA study. The parameters included the volume CT dose index (CTDIvol, mGy) and dose length product (DLP, mGy × cm). The mean and range of CTDIvol (mGy) and DLP (mGy × cm) for three respective year was (2018):10.8 (1.14-77.7) and 2369.8 ± 1231.4 (290.4-6188.9), (2019): 13.82 (1.13-348.5), and 2180.5 (501.8-9534.5) and (2020) 10.9 (0.7-52.9) and 1877.3 (149.4-5011.1), respectively. Patients' effective doses were higher compared to previous studies. Therefore, the CT acquisition parameter optimization is vital to reduce the dose to its minimal value.

Radiation Dose Assessment for Myocardial Perfusion Imaging: A Single Institution Survey

OBJECTIVE

This study aims to establish a local diagnostic reference level (LDRL) for single-photon emission tomography/computed tomography (SPECT/CT) and positron emission tomography/CT (PET/CT) with respect to myocardial perfusion imaging (MPI).

MATERIALS AND METHODS

The acquisition protocol and dosimetry data on the MPI procedures of five SPECT/CT scans and one PET/CT scan were collected. Data on technitum-99m sestamibi (^99mTc-sestamibi), ^99mTc-tetrofosmin, thallium-201 (²⁰¹Tl), and rubidium-82 (⁸²RB) were all collected from one centre via questionnaire booklets. Descriptive data analysis was used to analyse all variables, and the 50th percentile was used to analyse each radiation dose quantity.

RESULTS

The reported 50th percentile dose for a one-day stress/rest protocol using ^99mTc-sestamibi (445/1147 MBq) and ^99mTc-tetrofosmin (445/1147 MBq) and for a two-day stress/rest protocol using ^99mTc-sestamibi (1165/1184 MBq) and ^99mTc-tetrofosmin (1221/1184 MBq) are in good agreement with reported national diagnostic reference levels (NDRLs). However, the dose from the study data on a one-day stress/rest protocol using ^99mTc-sestamibi was more than the 50th percentile dose from the Brazilian data (370/1110 MBq) on a similar protocol, and the dose from the study data on a two-day stress/rest protocol using ^99mTc-tetrofosmin was more than the 50th percentile dose (1084/1110 MBq) from the United States data on MPI scans. Regarding the computed tomography (CT) portion of the SPECT/CT framework, the 50th percentile doses were lower than all the identified doses in the data considered in the literature reviewed. However, regarding the CT component of the PET/CT MPI scans, the ⁸²RB dose was more than the recorded doses in the CT data in the published literature.

CONCLUSION

This study determined the LDRL of five SPECT/CT protocols and one PET/CT MPI protocol. The results suggest that there may be opportunities to optimise the patient radiation burden from administered activities in patients undergoing SPECT examinations and the CT components associated with ⁸²RB PET/CT scans without compromising diagnostic image quality.

How should radiation exposure be handled in fluoroscopy-guided endoscopic procedures in the field of gastroenterology?

Fluoroscopy-guided endoscopic procedures (FGEPs) are rapidly gaining popularity in the field of gastroenterology. Radiation is a well-known health hazard. Gastroenterologists who perform FGEPs are required to protect themselves, patients, as well as nurses and radiologists engaged in examinations from radiation exposure. To achieve this, all gastroenterologists must first understand and adhere to the International Commission on Radiological Protection Publication. In particular, it is necessary to understand the three principles of radiation protection (Justification, Optimization, and Dose Limits), the As Low As Reasonably Achievable principle, and the Diagnostic Reference Levels (DRLs) according to them. This review will mainly explain the three principles of radiation exposure protection, DRLs, and occupational radiological protection in interventional procedures while introducing related findings. Gastroenterologists must gain knowledge of radiation exposure protection and keep it updated.

Radiation doses from low-dose CT scans in SPECT/CT and PET/CT examinations: A survey in Germany

AIM

Recently, dose reference levels (DRLs) have been defined in Germany for auxiliary low-dose CT scans in hybrid SPECT/CT and PET/CT examinations, based on data from 2016/17. Here, another survey from 2020 was evaluated and compared with the new DRLs as well as with similar surveys from foreign countries.

METHODS

The survey, which had already been conducted in the Nordic countries, queried for various examinations including the following values: patient weight and height, volume CT dose index (CTDI_vol), dose length product (DLP). For each examination, statistical parameters such as the third quartile (Q3) were determined from all submitted CTDI_vol and DLP values. Additionally, for examinations comprising datasets from at least 10 systems, the third quartile (Q3-Med) of the respective median values of each system was calculated. Q3 and Q3-Med were compared with the newly published DRLs from Germany and values from similar studies from other countries.

RESULTS

Data from 15 SPECT/CT and 13 PET/CT systems from 15 nuclear medicine departments were collected. For the following examinations datasets from more than 10 systems were submitted: SPECT lung VQ, SPECT bone, SPECT&PET cardiac, PET brain, PET oncology. Especially for examinations of the thorax and heart, the new DRLs are very strict compared to this study. The CTDI_vol values for examinations of the head were lower in this study than the DRLs prescribe now.

CONCLUSIONS

For certain examination types, there is a need for dose optimization at some clinics and devices in order to take into account the new DRLs in Germany in the future.

Medical Radiation Exposure Reduction in PET via Super-Resolution Deep Learning Model

In positron emission tomography (PET) imaging, image quality correlates with the injected [18F]-fluorodeoxyglucose (FDG) dose and acquisition time. If image quality improves from short-acquisition PET images via the super-resolution (SR) deep learning technique, it is possible to reduce the injected FDG dose. Therefore, the aim of this study was to clarify whether the SR deep learning technique could improve the image quality of the 50%-acquisition-time image to the level of that of the 100%-acquisition-time image. One-hundred-and-eight adult patients were enrolled in this retrospective observational study. The supervised data were divided into nine subsets for nested cross-validation. The mean peak signal-to-noise ratio and structural similarity in the SR-PET image were 31.3 dB and 0.931, respectively. The mean opinion scores of the 50% PET image, SR-PET image, and 100% PET image were 3.41, 3.96, and 4.23 for the lung level, 3.31, 3.80, and 4.27 for the liver level, and 3.08, 3.67, and 3.94 for the bowel level, respectively. Thus, the SR-PET image was more similar to the 100% PET image and subjectively improved the image quality, as compared to the 50% PET image. The use of the SR deep-learning technique can reduce the injected FDG dose and thus lower radiation exposure.

Diagnostic Reference Levels for nuclear medicine imaging in Austria: A nationwide survey of used dose levels for adult patients

PURPOSE

To assess dose levels in routine nuclear medicine (NUC) procedures in Austria as a prior to a legislative update of the National Diagnostic Reference Levels (NDRL).

METHOD

As part of a nationwide survey of common NUC-examinations between June 2019 and November 2019, data sets were collected from 33 Austrian hospitals with NUC equipment. All hospitals were asked to report the NUC imaging devices in use (model, type, year of manufacture, detector material, collimators), the standard protocol parameters for selected examinations (standard activity, collimator, average acquisition time, reconstruction type, use of time-of-flight) and to report data from 10 representative examinations (e.g. injected activity, weight), incl. the most common NUC-examinations for planar imaging/SPECT and PET. Median/mean values for injected activity were calculated and compared to current Austrian and international NDRL. A Pearson correlation coefficient was computed comparing different variables.

RESULTS

In total, all 33 hospitals (100% response rate) reported data for this study for 60 SPECT devices, 21 PET/CT devices and 23 scintigraphy devices. Fixed activity values for scintigraphy/SPECT and PET were employed by about 90% and 56% of the hospitals, respectively. The most widely performed examinations for scintigraphy/SPECT are bone imaging, thyroid imaging, renal imaging (with MAG3/EC) and lung perfusion imaging (in 88% of the hospitals) and F-18 FDG-PET studies for oncology indications (in 100% of the hospitals). Significant correlations were found for patient weight and injected activity (scintigraphy/SPECT), use of iterative reconstruction and injected activity (PET) as well as size of field-of-view and injected activity (PET).

CONCLUSIONS

The reported injected activity levels were comparable to those in other countries. However, for procedures for which NDRL exist, deviations in injected activities of >20% compared to the NDRL were found. These deviations are assumed to result mainly from advances in technology but also from deviations between NDRL and prescribed activities as given in the information leaflets of the radiopharmaceuticals.

Radiation Dose Modulation of Computed Tomography Component in Positron Emission Tomography/Computed Tomography

In oncology practice, the CT component of PET/CT may be used for attenuation correction, lesion localization, and CT diagnosis, and significantly enhances the clinical benefit of PET. However, acquisition of CT covering the whole body increases radiation dose and consequently the risk of cancer induction, and optimization should be pursued. In CT, radiation dose is a major determinant of image quality, and is mainly adjusted by modulation of tube current. Automatic exposure control (AEC) is widely used for tube current modulation, and increases tube current in a large patient and in strongly attenuating regions of a given patient to preserve image quality despite strong X-ray attenuation. Radiation dose determined by AEC depends on various factors, such as the type of AEC software, scout imaging direction, arm positioning, and patient centering. Because radiation dose reduction increases image noise and may degrade clinical utility, image quality should be assessed together with radiation dose in the process of optimization. Clinical demands for image quality vary largely depending on the aim of the CT component, with lower quality being sufficient for lesion localization than for CT diagnosis. Therefore, optimal radiation dose differs according to the aim. Determining optimal dose is a somewhat subjective and difficult task, and use of the diagnostic reference level, determined based on national or regional survey, is recommended to recognize need for optimization. The volume CT dose index and dose-length product are used as indices of CT radiation dose, and effective dose may also be calculated for comparison of stochastic effects among different radiation sources and among different imaging procedures. Wide coverage from the head to the lower extremities causes problems in estimating these indices in whole-body PET/CT. CT definitely enhances clinical benefits of PET but simultaneously increases potential detriments due to radiation exposure. In the era of hybrid imaging, nuclear medicine practitioners should be aware of the technology and radiation dose management of CT.

Optimization of injection dose in 18F-FDG PET/CT based on the 2020 national diagnostic reference levels for nuclear medicine in Japan

OBJECTIVE

Recently, the national diagnostic reference levels (DRLs) in Japan were revised as the DRLs 2020, wherein the body weight-based injection dose optimization in positron emission tomography/computed tomography using 18F-fluoro-2-deoxy-D-glucose (18F-FDG PET/CT) was first proposed. We retrospectively investigated the usefulness of this optimization method in improving image quality and reducing radiation dose.

METHODS

A total of 1,231 patients were enrolled in this study. A fixed injection dose of 240 MBq was administered to 624 patients, and a dose adjusted to 3.7 MBq/kg body weight was given to 607 patients. The patients with body weight-based injection doses were further divided according to body weight: group 1 (≤ 49 kg), group 2 (50-59 kg), group 3 (60-69 kg), and group 4 (≥ 70 kg). The effective radiation dose of FDG PET was calculated using the conversion factor of 0.019 mSv/MBq, per the International Commission on Radiological Protection publication 106. Image quality was assessed using noise equivalent count density (NECdensity), which was calculated by excluding the counts of the brain and bladder. The usefulness of the injection dose optimization in terms of radiation dose and image quality was analyzed.

RESULTS

The body weight-based injection dose optimization significantly decreased the effective dose by 11%, from 4.54 ± 0.1 mSv to 4.05 ± 0.8 mSv (p < 0.001). Image quality evaluated by NECdensity was also significantly improved by 10%, from 0.39 ± 0.1 to 0.43 ± 0.2 (p < 0.001). In no case did NECdensity deteriorate when the effective dose was decreased. In group 1, the dose decreased by 32%, while there was no significant deterioration in NECdensity (p = 0.054). In group 2, the dose decreased by 17%, and the NECdensity increased significantly (p < 0.01). In group 3, the dose decreased by 3%, and the NECdensity increased significantly (p < 0.01). In group 4, the dose increased by 14%, but there was no significant change in the NECdensity (p = 0.766).

CONCLUSION

Body weight-based FDG injection dose optimization contributed to not only the reduction of effective dose but also the improvement of image quality in patients weighing between 50 and 69 kg.

The radiation doses and radiation protection on the endoscopic retrograde cholangiopancreatography procedures

Although many interventions involving radiation exposure have been replaced to endoscopic procedure in the gastrointestinal and hepatobiliary fields, there remains no alternative for enteroscopy and endoscopic retrograde cholangiopancreatography (ERCP), which requires the use of radiation. In this review, we discuss the radiation doses and protective measures of endoscopic procedures, especially for ERCP. For the patient radiation dose, the average dose area product for diagnostic ERCP was 14-26 Gy.cm², while it increased to as high as 67-89 Gy.cm² for therapeutic ERCP. The corresponding entrance skin doses for diagnostic and therapeutic ERCP were 90 and 250 mGy, respectively. The mean effective doses were 3- 6 mSv for diagnostic ERCP and 12-20 mSv for therapeutic ERCP. For the occupational radiation dose, the typical doses were 94 μGy and 75 μGy for the eye and neck, respectively. However, with an over-couch-type X-ray unit, the eye and neck doses reached as high as 550 and 450 μGy, with maximal doses of up to 2.8 and 2.4 mGy/procedure, respectively.A protective lead shield was effective for an over couch X-ray tube unit. It lowered scattered radiation by up to 89.1% in a phantom study. In actual measurements, the radiation exposure of the endoscopist closest to the unit was reduced to approximately 12%. In conclusion, there is a clear need for raising awareness among medical personnel involved endoscopic procedures to minimise radiation risks to both the patients and staff.

NATIONAL DIAGNOSTIC REFERENCE LEVELS FOR NUCLEAR MEDICINE IN KUWAIT

The diagnostic reference level (DRL) is an optimization tool of patients exposure used to evaluate and provide guidance for radiation doses in medical imaging. In the past few decades, there has been a global increase in the number of diagnostic imaging procedures, including nuclear medicine procedures, and consequently the patient radiation exposure. This has encouraged international and national healthcare organizations to take actions and keep up with such changes to meet the expectations of an increasing use of ionizing radiation in medicine. The DRL in Kuwait was established by investigating the administered activity of radiopharmaceuticals and computed tomography (CT) radiation doses in hybrid imaging systems. The DRL were determined based on the 75th percentile of radiopharmaceuticals administered activity distribution as recommended by the international commission on radiation protection (ICRP). This study presents the establishment process and results of the first national DRLs for nuclear medicine procedures in Kuwait as a way to optimize radiation exposure. The DRLs determined in Kuwait are in good agreement with other published DRLs in Europe, Japan, Korea, Australia and the US.

Establishment of typical adult CT dose indicators for PET-CT scans in Slovenia

The aim was to determine typical values of diagnostic reference level (DRL) quantities for the computed tomography (CT) part of the most common positron emission tomography-computed tomography (PET-CT) procedures in Slovenia. The most common PET-CT procedures were identified, and data collated for 565 patients imaged in all three PET-CT units in Slovenia during a time span of 11 months. As the number of facilities is too low to establish national DRLs, we followed ICRP recommendations and determined typical values of DRL quantities as the median values of the pooled set of data. Mean, median, and standard deviation of CT dose index (CTDI_vol) and total dose length product (DLP) for the CT part of the most common PET-CT procedures were determined for pooled data as well as for each PET-CT unit. The data were compared between all three units to identify possible outliers that would likely benefit from optimization. Three most common CT protocols covering approximately 2/3 of all PET-CT imaging performed in Slovenia were considered: from the base of the cranium to the middle of the femur, from the top of the head to the middle of the femur, and for the whole-body PET-CT. The established typical values in terms of total DLP were 295, 359, and 676 mGyċcm, respectively; and in terms of CTDI_vol3.05, 3.22, and 3.60 mGy, respectively. Comparing the data between all three units showed significantly higher (p< 0.001) patient doses on one unit, indicating a need for optimization. The results present the first-time data on the national typical values of DRL quantities for the CT part of most common PET-CT procedures in Slovenia. While the determined typical values are within the DRL values established in some other countries, significant differences were found between the individual units included in the study.

Cumulative radiation doses from recurrent PET/CT examinations

Positron emission tomography (PET–CT) is an essential imaging modality for the management of various diseases. Increasing numbers of PET–CT examinations are carried out across the world and deliver benefits to patients; however, there are concerns about the cumulative radiation doses from these examinations in patients. Compared to the radiation exposure delivered by CT, there have been few reports on the frequency of patients with a cumulative effective radiation dose of ≥100 mSv from repeated PET–CT examinations. The emerging dose tracking system facilitates surveys on patient cumulative doses by PET–CT because it can easily wrap up exposure doses of PET radiopharmaceuticals and CT. Regardless of the use of a dose tracking system, implementation of justification for PET–CT examinations and utilisation of dose reduction measures are key issues in coping with the cumulative dose in patients. Despite all the advantages of PET/MRI such as eliminating radiation exposure from CT and providing good tissue contrast in MRI, it is expensive and cannot be introduced at every facility; thus, it is still necessary to utilise PET–CT with radiation reduction measures in most clinical situations.

Attenuation correction using deep learning for brain perfusion SPECT images

OBJECTIVE

Non-uniform attenuation correction using computed tomography (CT) improves the image quality and quantification of single-photon emission computed tomography (SPECT). However, it is not widely used because it requires a SPECT/CT scanner. This study constructs a convolutional neural network (CNN) to generate attenuation-corrected SPECT images directly from non-attenuation-corrected SPECT images.

METHODS

We constructed an auto-encoder (AE) using a CNN to correct the attenuation in brain perfusion SPECT images. SPECT image datasets of 270 (44,528 slices including augmentation), 60 (5002 slices), and 30 (2558 slices) cases were used for training, validation, and testing, respectively. The acquired projection data were reconstructed in three patterns: uniform attenuation correction using Chang's method (Chang-AC), non-uniform attenuation correction using CT (CT-AC), and no attenuation correction (No-AC). The AE learned an end-to-end mapping between the No-AC and CT-AC images. The No-AC images in the test dataset were loaded into the trained AE, which generated images simulating the CT-AC images as output. The generated SPECT images were employed as attenuation-corrected images using the AE (AE-AC). The accuracy of the AE-AC images was evaluated in terms of the peak signal-to-noise ratio (PSNR) and the structural similarity metric (SSIM). The intensities of the AE-AC and CT-AC images were compared by voxel-by-voxel and region-by-region analysis.

RESULTS

The PSNRs of the AE-AC and Chang-AC images, compared using CT-AC images, were 62.2, and 57.9, and their SSIM values were 0.9995 and 0.9985, respectively. The AE-AC and CT-AC images were visually and statistically in good agreement.

CONCLUSIONS

The proposed AE-AC method yields highly accurate attenuation-corrected brain perfusion SPECT images.