Assessment of patients' cumulative doses in one year and collective dose to population through CT examinations

Dose, dose, dose, but where is the patient dose?

The article reviews the historical developments in radiation dose metrices in medical imaging. It identifies the good, the bad, and the ugly aspects of current-day metrices. The actions on shifting focus from International Commission on Radiological Protection (ICRP) Reference-Man-based population-average phantoms to patient-specific computational phantoms have been proposed and discussed. Technological developments in recent years involving AI-based automatic organ segmentation and 'near real-time' Monte Carlo dose calculations suggest the feasibility and advantage of obtaining patient-specific organ doses. It appears that the time for ICRP and other international organizations to embrace 'patient-specific' dose quantity representing risk may have finally come. While the existing dose metrices meet specific demands, emphasis needs to be also placed on making radiation units understandable to the medical community.

Cumulative radiation exposure from multimodality recurrent imaging of CT, fluoroscopically guided intervention, and nuclear medicine

OBJECTIVES

To assess cumulative effective dose (CED) over a 4-year period in patients undergoing multimodality recurrent imaging at a major hospital in the USA.

METHODS

CED from CT, fluoroscopically guided intervention (FGI), and nuclear medicine was analyzed in consecutive exams in a tertiary care center in 2018-2021. Patients with CED ≥ 100 mSv were classified by age and body habitus (underweight, healthy weight, overweight, obese), as per body mass index percentiles < 5th, 5th to < 85th, 85th to < 95th, and ≥ 95th (age 2-19 years), and its ranges < 18.5, 18.5-24.9, 25-29.9, and ≥ 30 (≥ 20 years), respectively.

RESULTS

Among a total of 205,425 patients, 5.7% received CED ≥ 100 mSv (mean 184 mSv, maximum 1165 mSv) and their ages were mostly 50-64 years (34.1%), followed by 65-74 years (29.8%), ≥ 75 years (19.5%), 20-49 years (16.3%), and ≤ 19 years (0.29%). Body habitus in decreasing occurrence was obese (38.6%), overweight (31.9%), healthy weight (27.5%), and underweight (2.1%). Classification by dose indicated 172 patients (≥ 500 mSv) and 3 (≥ 1000 mSv). In comparison, 5.3% of 189,030 CT patients, 1.6% of 18,963 FGI patients, and 0.19% of 41,401 nuclear-medicine patients received CED ≥ 100 mSv from a single modality.

CONCLUSIONS

The study of total dose from CT, FGI, and nuclear medicine of patients with CED ≥ 100 mSv indicates major (89%) contribution of CT to CED with 70% of cohort being obese and overweight, and 64% of cohort aged 50-74 years.

CLINICAL RELEVANCE STATEMENT

Multimodality recurrent exams are common and there is a lack of information on patient cumulative radiation exposure. This study attempts to address this lacuna and has the potential to motivate actions to improve the justification process for enhancing patient safety.

KEY POINTS

• In total, 5.7% of patients undergoing multimodality recurrent imaging (CT, fluoroscopically guided intervention, nuclear medicine) incurred a dose of ≥ 100 mSv. • Mean dose was 184 mSv, with 15 to 18 times contribution from CT than that from fluoroscopically guided intervention or nuclear medicine. • In total, 70% of those who received ≥ 100mSv were either overweight or obese.

Is a one percent occurrence of high-dose patients significant?

Risk-free society is utopian. We come across risks in everyday life, and we use probabilities to get a feel of how risky a situation is. Risk probability numbers of around 1% are comforting, but an intercomparison of numbers among various low risks in popular situations can be enlightening. In this article, we compare risks of complications or death in several surgeries and risks in commercial air travel with risks for patients getting cumulative effective dose (CED) of 100 mSv or more, as the latter is a hot and controversial topic currently. The analysis shows that many common surgeries are a few tens or hundreds of times less risky than the risk from a 100 mSv dose, even though the former often frightens us more. Despite there being a much higher chance of developing cancer from radiation than being involved in a commercial plane accident, there is much less emphasis on patient radiation safety than aviation safety. Further, a look at the system of control on prescription drugs indicates that there is much to learn for policy planning. This analysis may help the International Commission on Radiological Protection (ICRP) in their review of recommendations.

Optimisation of protection in the medical exposure of recurrent adult patients due to computed tomography procedures: development of recurrent exposures reference levels

OBJECTIVES

To assess the incidence (1 year) and the cumulative incidence (3 years) of the condition of patients accruing cumulative effective doses (CED) of ≥ 100 mSv and their variability among different hospitals. To establish and validate a reference level for the CED in patients with recurrent exposures (RERL) and provide a RERL value.

METHODS

Data of CT exposure was collected in 9 similar hospitals. The database included 294,222 patient*years who underwent 442,278 CT exams in 3 years. The incidence proportion of patients with CED ≥ 100 mSv in a given year (I100;1) and the 3-year cumulative incidence of patients with CED ≥ 100 mSv over 3 consecutive years (I100;3) were calculated and compared among different institutions.

RESULTS

I100;1 ranged from a minimum of 0.1% to a maximum of 5.1%. The percentage of recurrent patients was quite uniform among centres ranging from 23 to 38%. The I100;3 ranged from a minimum of 1.1 to 11.4%. There was a strong positive correlation between the third quartile values of yearly CED and yearly incidence (r = 0.90; R2 = 0.81; p < 0.0001). RERL value in our study was found at 34.0 mSv.

CONCLUSION

The management of patients with recurrent exposures is highly variable among hospitals leading to a 50-fold variation in I100;1 and to a tenfold variation in I100;3. RERL could be established and used by taking as a RERL quantity the CED and as a RERL value the 75th percentile of the third quartiles of the distribution of the yearly CED obtained by surveying different hospitals.

CLINICAL RELEVANCE STATEMENT

This is the first ever multicentre study that quantifies recurrent exposures in terms of incidence and cumulative incidence of patients with CED ≥ 100 mSv. RERL establishment and use could benefit the optimisation of radioprotection of patients with recurrent exposures.

KEY POINTS

This is the first multicentre study estimating yearly incidence and 3-year cumulative incidence of patients with cumulative effective doses ≥ 100 mSv. In this study, a 50-fold inter centre variation between the maximum (5.1%) and the minimum value (0.1%) of yearly incidence of patients with cumulative effective doses ≥ 100 mSv was reported. The range of the 3-year cumulative incidence extended from 1.1 to 11.4% (a tenfold variation) The third quartile of the yearly cumulative effective doses in a centre showed a strong positive correlation with the yearly incidence of patients with cumulative effective doses ≥ 100 mSv, with a potential of being used to set reference levels for recurrent exposures.

Deep learning-driven multi-view multi-task image quality assessment method for chest CT image

BACKGROUND

Chest computed tomography (CT) image quality impacts radiologists' diagnoses. Pre-diagnostic image quality assessment is essential but labor-intensive and may have human limitations (fatigue, perceptual biases, and cognitive biases). This study aims to develop and validate a deep learning (DL)-driven multi-view multi-task image quality assessment (M[Formula: see text]IQA) method for assessing the quality of chest CT images in patients, to determine if they are suitable for assessing the patient's physical condition.

METHODS

This retrospective study utilizes and analyzes chest CT images from 327 patients. Among them, 1613 images from 286 patients are used for model training and validation, while the remaining 41 patients are reserved as an additional test set for conducting ablation studies, comparative studies, and observer studies. The M[Formula: see text]IQA method is driven by DL technology and employs a multi-view fusion strategy, which incorporates three scanning planes (coronal, axial, and sagittal). It assesses image quality for multiple tasks, including inspiration evaluation, position evaluation, radiation protection evaluation, and artifact evaluation. Four algorithms (pixel threshold, neural statistics, region measurement, and distance measurement) have been proposed, each tailored for specific evaluation tasks, with the aim of optimizing the evaluation performance of the M[Formula: see text]IQA method.

RESULTS

In the additional test set, the M[Formula: see text]IQA method achieved 87% precision, 93% sensitivity, 69% specificity, and a 0.90 F1-score. Extensive ablation and comparative studies have demonstrated the effectiveness of the proposed algorithms and the generalization performance of the proposed method across various assessment tasks.

CONCLUSION

This study develops and validates a DL-driven M[Formula: see text]IQA method, complemented by four proposed algorithms. It holds great promise in automating the assessment of chest CT image quality. The performance of this method, as well as the effectiveness of the four algorithms, is demonstrated on an additional test set.

Automatic organ completion with image stitching for personalized radiation dosimetry in CT examinations

PURPOSE

Computed tomography (CT) image-based patient-specific voxel-based dosimetry has difficulties complementing missing tissues for organs located partially inside or completely outside the image volume. Previous studies constructed patient-specific whole-body models by rescaling reference phantoms or extending regional CT images with manually adjusted phantoms. This study proposes a methodology for automatic organ completion of regional CT images for CT dosimetry using a stitching approach.

METHODS

Virtual clinical trials were performed by truncating whole-body CT images to generate virtual clinical chest and abdominopelvic CT images. Corresponding anchor images for each patient were selected according to sex and similarity of the axial length and water equivalent diameter of the virtual regional CT images. Automatic image stitching was performed by transformation initialization and iteration, while the stitched CT images and organ atlas were used in GPU-based Geant4 Monte Carlo simulations to generate a radiation dose map and absorbed organ dose. To evaluate the performance of the stitching model in radiation dosimetry, organ mass differences and Jaccard's coefficient of stitched and rescaled anchor images were calculated, and the radiation doses were compared among the corresponding values from the VirtualDose®, original whole-body CT, stitching model, regional CT, registration-based rescaling method, and WED-based rescaling method.

RESULTS

The anatomical accuracy of stitched images was significantly improved. For organs partially inside the image volume, organ dose estimation from the stitching model could be more accurate than that reported in previous studies. The absolute differences in effective dose from the stitched images were 6.55% and 4.81% for chest and abdominopelvic CT scans, respectively.

CONCLUSION

The proposed automatic stitching model partially complements organs inside or outside the CT scan range and provides more accurate anatomical representations for radiation dosimetry than traditional phantom rescaling methods.

Accounting for radiation exposure from previous CT exams while deciding on the next exam: What do referring clinicians think?

PURPOSE

To obtain clinicians' views of the need to account for radiation exposure from previous CT scans and the advisability of a regulatory mechanism to control the number of CT scans for an individual patient.

METHODS

A convenience survey was conducted by emailing a link to a three-question electronic survey to clinicians in many countries, mostly through radiology and radiation protection contacts.

RESULTS

505 responses were received from 24 countries. 293 respondents (58%) understand that current regulations do not limit the number of CT scans that can be prescribed for a single patient in a year. When asked whether there should be a regulation to limit the number of CT scans that can be prescribed for a single patient in one year, only a small fraction (143, 28%) answered 'No', 182 (36%) answered 'Maybe' and 166 (33%) answered 'Yes'. Most respondents (337; 67%) think that radiation risk should form part of the consideration when deciding whether to request a CT exam. A minority (138; 27%) think the decision should be based only on the medical indication for the CT exam. Comparison among the 4 countries (South Korea, Hungary, USA and Canada) with the largest number of respondents indicated wide variations in responses.

CONCLUSIONS

A majority of the surveyed clinicians consider radiation risk, in addition to clinical factors, when prescribing CT exams. Most respondents are in favor of, or would consider, regulation to control the number of CT scans that could be performed on a patient annually.

T-shirt size as a classification for body habitus in computed tomography (CT) and development of size-based dose reference levels for different indications

PURPOSE

To examine the impact of patient size on dose indices and develop size-based reference levels (50th and 75th percentiles) for 20 body CT exams for routine and organ-specific clinical indications.

METHODS

Based on effective diameter estimated from adult body CT, each acquisition was classified into T-shirt size as XXS, XS, S, M, L, XL, and XXL. Radiation dose indices for each size and each exam type were correlated.

RESULTS

About 0.93 million CT exams from 256 CT facilities in the United States were analysed. Taking T-shirt size M as a reference, the CTDI_vol for other sizes were: XXS (∼60%), XS (∼65%), S (∼75%), L (∼130%), XL (∼165%), XXL (∼210%), or grossly small patients received about 60% of the dose as compared to M sized patients and XXL required doubling the dose. Taking ratio of the dose indices of the largest to smallest size, it was evident that SSDE variation was much less (about 50%) than that in CTDI_vol, but there was still nearly 40 to 220% variation in SSDE across the range of t-shirt sizes. The 50th and 75th percentile values are presented for CTDI_vol, SSDE and DLP for each of the 20 CT exams and for each of the seven T-shirt sizes.

CONCLUSIONS

A novel approach expressing body habitus in terms of T-shirt size is not only simple and intuitive, but it also provides a tool to have a perception of differences in dose metrices among patients of different body build.