Use of effective dose in medicine

The impact of X-ray scatter correction software on abdomen radiography in terms of image quality and radiation dose

INTRODUCTION

The conventional anti-scatter grid is widely used in X-ray radiography to reduce scattered X-rays, but it increases patient dose. Scatter-correction software offers a dose-reducing alternative by correcting for scattered X-rays without a physical grid. Grids and software correction are necessary to reduce scatter radiation and improve image quality especially for the large body parts. The scatter correction can be beneficial in situations where the use of grid is challenging. The implementation of grids and advanced software correction techniques is imperative to ensure that radiographic images maintain high levels of clarity, contrast, and resolution, and ultimately facilitating more accurate diagnoses. This study compares image quality and radiation dose for abdomen exams using scatter correction software and physical grids.

METHODS

An anthropomorphic phantom (abdomen) underwent imaging with varying fat and lean tissue layers and body mass index (BMI) configurations. Imaging parameters included 70 kVp tube voltage, 110 cm SID, and Automatic Exposure Control (AEC) both lateral and central chambers. AP abdomen X-ray projections were acquired with and without an anti-scatter grid, and scatter correction software was applied. Image quality was assessed using contrast to noise ratio (CNR) and signal to noise ratio (SNR) metrics. The tube current mAs was considered an exposure factor that affected radiation dose and was used to compare the VG software and physical grid. Radiation dose was measured using Dose Area Products (DAP). The effective dose was estimated using Monte Carlo simulation-PCXMC software. Paired t-tests were used to investigate the image quality difference between the Gridless and VG software, Gridless and PG, and VG software and PG approaches. For the DAP and effective dose, paired t-test was used to investigate the difference between VG software and PG.

RESULTS

Images acquired with a grid had the highest mean CNR (71.3 ± 32) compared to Gridless (50 ± 33.8) and scatter correction software (59.3 ± 37.9). The mean SNR of the grid images was (82.7.3 ± 38.9), which is 18% higher than the scatter correction software images (70.4 ± 36.7) and 29% higher than in the Gridless images (62.9.3 ± 34). The mean DAP value was reduced by 81% when the scatter correction software was used compared to the grid (mean: 65.4 μGy.m2 and 338.2 μGy.m2, respectively) with a significant difference (p = 0.001). Scatter correction software resulted in a lower effective dose compared to physical grid use, (mean difference± SD = -0.3 ± 0.18 mSv) with a significant difference (P = 0.02).

CONCLUSION

Scatter correction software reduced the radiation dose required but images employing a grid yielded higher CNR and SNR. However, the radiation dose reduction might affect the image quality to a level that impacts the diagnostic information available. Thus, further research needs to be conducted to optimise the use of the scatter correction software.

IMPLICATION FOR PRACTICE

Objectively, X-ray scatter correction software might be promising in conditions where a grid cannot be applied.

Influence of resident involvement on fluoroscopy time and ionizing radiation exposure in fluoroscopy-guided spinal procedures

BACKGROUND

Fluoroscopic guidance has become the standard for a variety of medical procedures. Mastering these techniques requires practice, which may entail additional radiation for patients and providers. Despite their widespread use, the literature examining factors influencing radiation exposure in fluoroscopically guided pain procedures is scarce.

OBJECTIVE

To evaluate the influence of resident involvement on radiation exposure during fluoroscopy-guided spinal interventions.

DESIGN

Single-center, observational study.

SETTING

Outpatient physiatry clinic in a teaching hospital.

PATIENTS

All patients who received cervical or lumbar facet block(s) (FBs), transforaminal epidural steroid injection(s) (TFESIs) without digital subtraction, or a caudal epidural (CE) during the study period were included.

INTERVENTIONS

Resident involvement in the procedures: absent, observing, or participating.

MAIN OUTCOME MEASURES

Machine-indicated fluoroscopy time (seconds) and radiation dose (milligrays [mGy]).

RESULTS

Two hundred ninety six procedures were included: 188 FBs (58 cervical, 130 lumbar), 48 CEs, and 60 TFESIs. For lumbar FBs, fluoroscopy time and radiation dose increased significantly when residents performed them (meantime  = 24.5 s, confidence interval [CI] = 20.4-28.7; meandose  = 3.53 mGy, CI = 2.57-4.49) compared to when they observed (meantime  = 9.9 s, CI = 8.1-11.7; meandose  = 1.28 mGy, CI = 0.98-1.59) (mean difference: time = 14.63 s, CI = 9.31-19.94; dose = 2.25 mGy, CI = 1.17-3.33) and were absent during the procedure (meantime  = 12.9 s, CI = 11.1-14.6; meandose  = 1.65 mGy, CI = 1.40-1.89) (mean difference: time = 11.67 s, CI = 7.35-15.98; dose = 1.88 mGy, CI = 1.01-2.76). In the case of TFESIs, time, but not dose, increased significantly when residents observed (meantime  = 39.1 s, CI = 30.7-47.6; meandose  = 6.73 mGy, CI = 3.39-10.07) compared to when they were absent (meantime  = 27.1 s, CI = 22.4-31.8; meandose  = 4.41 mGy, CI = 3.06-5.76 (mean difference: time = 11.99 s, CI = 1.37-22.61; dose = 2.32 mGy, CI = -1.20-5.84). Finally, resident involvement did not significantly affect the outcomes for CEs (ptime  = .032, pdose  = .74) and cervical FBs (ptime  = .64, pdose  = .68).

CONCLUSION

Resident participation affected lumbar FBs the most, with an increase in both fluoroscopy time and radiation dose.

Patient-level dose monitoring in computed tomography: tracking cumulative dose from multiple multi-sequence exams with tube current modulation in children

BACKGROUND

In children exposed to multiple computed tomography (CT) exams, performed with varying z-axis coverage and often with tube current modulation, it is inaccurate to add volume CT dose index (CTDI_vol) and size-specific dose estimate (SSDE) to obtain cumulative dose values.

OBJECTIVE

To introduce the patient-size-specific z-axis dose profile and its dose line integral (DLI) as new dose metrics, and to use them to compare cumulative dose calculations against conventional measures.

MATERIALS AND METHODS

In all children with 2 or more abdominal-pelvic CT scans performed from 2013 through 2019, we retrospectively recorded all series kV, z-axis tube current profile, CTDI_vol, dose-length product (DLP) and calculated SSDE. We constructed dose profiles as a function of z-axis location for each series. One author identified the z-axis location of the superior mesenteric artery origin on each series obtained to align the dose profiles for construction of each patient's cumulative profile. We performed pair-wise comparisons between the peak dose of the cumulative patient dose profile and ΣSSDE, and between ΣDLI and ΣDLP.

RESULTS

We recorded dose data in 143 series obtained in 48 children, ages 0-2 years (n=15) and 8-16 years (n=33): ΣSSDE 12.7±6.7 and peak dose 15.1±8.1 mGy, ΣDLP 278±194 and ΣDLI 550±292 mGy·cm. Peak dose exceeded ΣSSDE by 20.6% (interquartile range [IQR]: 9.9-26.4%, P<0.001), and ΣDLI exceeded ΣDLP by 114% (IQR: 86.5-147.0%, P<0.001).

CONCLUSION

Our methodology represents a novel approach for evaluating radiation exposure in recurring pediatric abdominal CT examinations, both at the individual and population levels. Under a wide range of patient variables and acquisition conditions, graphic depiction of the cumulative z-axis dose profile across and beyond scan ranges, including the peak dose of the profile, provides a better tool for cumulative dose documentation than simple summations of SSDE. ΣDLI is advantageous in characterizing overall energy absorption over ΣDLP, which significantly underestimated this in all children.

Optimization of newly developed and lead shields thicknesses for protecting taxi drivers from 99mTc injected patients

Presently, public members are exposed to sources of ionizing radiation, and health risks due to radiation exposures should be a concern. This study aims to calculate the whole-body cumulative radiation exposure of taxi drivers. Also, this study will provide the effect of using a simple lead shield and three types of glass shield AVT6, TZN-D, and SLGC-E5, by calculating the effective annual dose of the taxi drivers that work in medical centers. Two MIRD phantoms as a driver and patient, a sample body of a taxi, pure lead, and glass sheets as a shield, were simulated using the MCNP code. We assumed that the patients had undergone the brain, liver, and kidney SPECT imaging by injecting 99mTC-HMPAO, 99mTC-sulfur colloid, and 99mTC-DMSA with the activity of 740MBq, 185MBq, and 333MBq, respectively. These shields are simulated on two sides of the driver, in the back and right side. The annual effective dose was calculated for 0-3.5 g/cm² area densities. It was observed that the 0.45, 1.09, 1.28, and 2.11 g/cm² of Pb, TZN-D, AVT6, and SLGC-E5 respectively decrease the effective dose below the allowed limit. According to the results, using the lead shield, the effective dose was reduced by a factor up to 7.25 times. It is recommended that taxi drivers wear a 0.4 mm lead shield or its equivalent when they have Tc-99 m injected patients.

Internal doses from radionuclides and their health effects following the Fukushima accident

This paper presents an overview of current internal dose estimates from the Fukushima accident, potential population specific uncertainties in these estimates are investigated, along with the relative effects of internal and external exposures. Thyroid doses were largely due to ¹³¹I, but variations in thyroid weight and fractional uptake and retention times of ¹³¹I in the thyroid contribute to uncertainties in thyroid dose estimates. Lower values for these parameters in the Japanese population, as compared to international reference assumptions, would lead to underestimation of doses on the basis of reference thyroid weights and overestimation of doses using reference thyroid uptake and retention times. Any overall bias in thyroidal doses due to population specific factors is the net result of the balance between these effects. Internal doses to other organs are largely due to ¹³⁴Cs and ¹³⁷Cs and their whole body distribution, population specific differences in these dose estimates are driven by average body mass, due to the inverse relationship between this and retention times. Potential differences in dose estimates and any inferred risks, due to local population specific factors, may be less than a factor of two for children and male adults, but the potential difference may be slightly underestimated for female adults. Recent micro-dosimetric studies have confirmed the existing perception that risk from internal exposures to ¹³⁷Cs, ¹³⁴Cs, and ¹³¹I should be nearly equivalent to that from external exposure to gamma rays at the same absorbed dose. Epidemiological studies provide comparisons between external and internal exposures to ¹³¹I in children and suggest that effects of internal exposure are similar to those of external exposure. Effective dose has been formulated to harmonise internal and external exposure risks for radiation protection purposes. On the basis of this review, the use of effective dose in this context does not seem to be unreasonable.

The mandate and work of ICRP Committee 2 on doses from radiation exposure

The practical implementation of the International Commission on Radiological Protection's (ICRP) system of radiological protection requires the availability of appropriate methodology and data. Over many years, ICRP Committee 2 has provided sets of dose coefficients to allow users to evaluate equivalent and effective doses for radiation exposures of workers and members of the public. The methodology being applied in the calculation of doses is state-of-the-art in terms of the biokinetic models used to describe the behaviour of inhaled and ingested radionuclides, and the dosimetric models used to model radiation transport for external and internal exposures. This overview provides an outline of recent work and future plans, including publications on dose coefficients for adults, children, and in-utero exposures, with new dosimetric phantoms in each case. For the first time, ICRP will publish dose coefficients for intakes of radon isotopes calculated using dosimetric models. Committee 2 is also working with Committee 3 on dose coefficients for radiopharmaceuticals, and leading a cross-committee initiative to provide advice on the use of effective dose. The remit of Committee 2 has now been widened to include all data requirements for the assessment of doses to humans and non-human biota.

Appropriate Use of Effective Dose in Radiation Protection and Risk Assessment

Effective dose was introduced by the ICRP for the single, over-arching purpose of setting limits for radiation protection. Effective dose is a derived quantity or mathematical construct and not a physical, measurable quantity. The formula for calculating effective dose to a reference model incorporates terms to account for all radiation types, organ and tissue radiosensitivities, population groups, and multiple biological endpoints. The properties and appropriate applications of effective dose are not well understood by many within and outside the health physics profession; no other quantity in radiation protection has been more confusing or misunderstood. According to ICRP Publication 103, effective dose is to be used for "prospective dose assessment for planning and optimization in radiological protection, and retrospective demonstration of compliance for regulatory purposes." In practice, effective dose has been applied incorrectly to predict cancer risk among exposed persons. The concept of effective dose applies generally to reference models only and not to individual subjects. While conceived to represent a measure of cancer risk or heritable detrimental effects, effective dose is not predictive of future cancer risk. The formula for calculating effective dose incorporates committee-selected weighting factors for radiation quality and organ sensitivity; however, the organ weighting factors are averaged across all ages and both genders and thus do not apply to any specific individual or radiosensitive subpopulations such as children and young women. Further, it is not appropriate to apply effective dose to individual medical patients because patient-specific parameters may vary substantially from the assumptions used in generalized models. Also, effective dose is not applicable to therapeutic uses of radiation, as its mathematical underpinnings pertain only to observed late (stochastic) effects of radiation exposure and do not account for short-term adverse tissue reactions. The weighting factors incorporate substantial uncertainties, and linearity of the dose-response function at low dose is uncertain and highly disputed. Since effective dose is not predictive of future cancer incidence, it follows that effective dose should never be used to estimate future cancer risk from specific sources of radiation exposure. Instead, individual assessments of potential detriment should only be based on organ or tissue radiation absorbed dose, together with best scientific understanding of the corresponding dose-response relationships.

Patient radiation doses in paediatric interventional cardiology procedures: a review

A large number of investigations into the radiation doses from x-ray guided interventional cardiology procedures in children have been carried out in recent years. A review was conducted of these studies, gathering data on kerma area product (P KA), fluoroscopic screening time (FT), air kerma, and estimates of effective dose and organ doses. The majority of studies focus on P KA and FT with no estimation of dose to the patient. A greater than ten-fold variation in average P KA was found between different studies, even where data were stratified by patient age or weight. Typical values of P KA were 0.6-10 Gy · cm2 (<1 year/10 kg), 1.5-30 Gy · cm2 (1-5 years), 2-40 Gy · cm2 (5-10 years), 5-100 Gy · cm2 (10-16 years) and 10-200 Gy · cm2 (>16 years). P KA was lowest for heart biopsy (0.3-10 Gy · cm2 for all ages combined) and atrial septostomy (0.4-4.0 Gy · cm2), and highest for pulmonary artery angioplasty (1.5-35 Gy · cm2) and right ventricular outflow tract dilatation (139 Gy · cm2). Most estimates of patient dose were in the form of effective dose (typically 3-15 mSv) which is of limited usefulness in individualised risk assessment. Few studies estimated organ doses. Despite advances in radiation protection, recent publications have reported surprisingly large doses, as represented by P KA and air kerma. There is little indication of a fall in these dose indicators over the last 15 years. Nor is there much suggestion of a fall in doses associated with the use of flat panel detectors, as opposed to image intensifiers. An assessment of the impact of radiation dose in the context of overall patient outcome is required.

Use of effective dose

International Commission on Radiological Protection (ICRP) Publication 103 provided a detailed explanation of the purpose and use of effective dose and equivalent dose to individual organs and tissues. Effective dose has proven to be a valuable and robust quantity for use in the implementation of protection principles. However, questions have arisen regarding practical applications, and a Task Group has been set up to consider issues of concern. This paper focusses on two key proposals developed by the Task Group that are under consideration by ICRP: (1) confusion will be avoided if equivalent dose is no longer used as a protection quantity, but regarded as an intermediate step in the calculation of effective dose. It would be more appropriate for limits for the avoidance of deterministic effects to the hands and feet, lens of the eye, and skin, to be set in terms of the quantity, absorbed dose (Gy) rather than equivalent dose (Sv). (2) Effective dose is in widespread use in medical practice as a measure of risk, thereby going beyond its intended purpose. While doses incurred at low levels of exposure may be measured or assessed with reasonable reliability, health effects have not been demonstrated reliably at such levels but are inferred. However, bearing in mind the uncertainties associated with risk projection to low doses or low dose rates, it may be considered reasonable to use effective dose as a rough indicator of possible risk, with the additional consideration of variation in risk with age, sex and population group.

Overview of ICRP Committee 2: doses from radiation exposure

The focus of the work of Committee 2 of the International Commission on Radiological Protection (ICRP) is the computation of dose coefficients compliant with Publication 103 A set of reference computational phantoms is being developed, based on medical imaging data, and used for radiation transport calculations. Biokinetic models used to describe the behaviour of radionuclides in body tissues are being updated, also leading to changes in organ doses and effective dose coefficients. Dose coefficients for external radiation exposure of adults calculated using the new reference phantoms were issued as Publication 116, jointly with the International Commission on Radiation Units and Measurements. Forthcoming reports will provide internal dose coefficients for radionuclide inhalation and ingestion by workers, and associated bioassay data. Work is in progress to revise internal dose coefficients for members of the public, and, for the first time, to provide reference values for external exposures of the public. Committee 2 is also working with Committee 3 on dose coefficients for radiopharmaceuticals, and leading a cross-Committee initiative to give advice on the use of effective dose.

Absorbed Doses and Risk Estimates of (211)At-MX35 F(ab')2 in Intraperitoneal Therapy of Ovarian Cancer Patients

PURPOSE

Ovarian cancer is often diagnosed at an advanced stage with dissemination in the peritoneal cavity. Most patients achieve clinical remission after surgery and chemotherapy, but approximately 70% eventually experience recurrence, usually in the peritoneal cavity. To prevent recurrence, intraperitoneal (i.p.) targeted α therapy has been proposed as an adjuvant treatment for minimal residual disease after successful primary treatment. In the present study, we calculated absorbed and relative biological effect (RBE)-weighted (equivalent) doses in relevant normal tissues and estimated the effective dose associated with i.p. administration of (211)At-MX35 F(ab')2.

METHODS AND MATERIALS

Patients in clinical remission after salvage chemotherapy for peritoneal recurrence of ovarian cancer underwent i.p. infusion of (211)At-MX35 F(ab')2. Potassium perchlorate was given to block unwanted accumulation of (211)At in thyroid and other NIS-containing tissues. Mean absorbed doses to normal tissues were calculated from clinical data, including blood and i.p. fluid samples, urine, γ-camera images, and single-photon emission computed tomography/computed tomography images. Extrapolation of preclinical biodistribution data combined with clinical blood activity data allowed us to estimate absorbed doses in additional tissues. The equivalent dose was calculated using an RBE of 5 and the effective dose using the recommended weight factor of 20. All doses were normalized to the initial activity concentration of the infused therapy solution.

RESULTS

The urinary bladder, thyroid, and kidneys (1.9, 1.8, and 1.7 mGy per MBq/L) received the 3 highest estimated absorbed doses. When the tissue-weighting factors were applied, the largest contributors to the effective dose were the lungs, stomach, and urinary bladder. Using 100 MBq/L, organ equivalent doses were less than 10% of the estimated tolerance dose.

CONCLUSION

Intraperitoneal (211)At-MX35 F(ab')2 treatment is potentially a well-tolerated therapy for locally confined microscopic ovarian cancer. Absorbed doses to normal organs are low, but because the effective dose potentially corresponds to a risk of treatment-induced carcinogenesis, optimization may still be valuable.