Patient radiation biological risk in computed tomography angiography procedure

Computed tomography angiography (CTA) has become the most valuable imaging modality for the diagnosis of blood vessel diseases; however, patients are exposed to high radiation doses and the probability of cancer and other biological effects is increased. The objectives of this study were to measure the patient radiation dose during a CTA procedure and to estimate the radiation dose and biological effects.The study was conducted in two radiology departments equipped with 64-slice CT machines (Aquilion) calibrated according to international protocols. A total of 152 patients underwent brain, lower limb, chest, abdomen, and pelvis examinations. The effective radiation dose was estimated using ImPACT scan software. Cancer and biological risks were estimated using the International Commission on Radiological Protection (ICRP) conversion factors.The mean patient dose value per procedure (dose length product [DLP], mGy·cm) for all examinations was 437.8 ± 166, 568.8 ± 194, 516.0 ± 228, 581.8 ± 175, and 1082.9 ± 290 for the lower limbs, pelvis, abdomen, chest, and cerebral, respectively. The lens of the eye, uterus, and ovaries received high radiation doses compared to thyroid and testis. The overall patient risk per CTA procedure ranged between 15 and 36 cancer risks per 1 million procedures. Patient risk from CTA procedures is high during neck and abdomen procedures. Special concern should be provided to the lens of the eye and thyroid during brain CTA procedures. Patient dose reduction is an important consideration; thus, staff should optimize the radiation dose during CTA procedures.     

Eye lens dosimetry and the study on radiation cataract in interventional cardiologists

PurposeTo determine the eye lens dose of the Interventional Cardiology (IC) personnel using optically stimulated luminescent dosimeter (OSLD) and the prevalence and risk of radiation – associated lens opacities in Thailand.Methods and results48 IC staff, with age- and sex- matches 37 unexposed controls obtained eye examines. Posterior lens change was graded using a modified Merriam-Focht technique by two independent ophthalmologists. Occupational exposure (mSv) was measured in 42 IC staff, using 2 OSLD badges place at inside lead apron and at collar. Annual eye lens doses (mSv) were also measured using 4 nanoDots OSL placed outside and inside lead glass eyewear. The prevalence of radiation-associated posterior lens opacities was 28.6% (2/7) for IC, 19.5% (8/41) for nurses, and 2.7% (1/37) for controls. The average and range of annual whole body effective dose, Hp(10), equivalent dose at skin of the neck, Hp(0.07) and equivalent dose at eye lens, Hp(3) were 0.80 (0.05–6.79), 5.88 (0.14–35.28), and 5.73 (0.14–33.20) mSv respectively. The annual average and range of eye lens dose using nano Dots OSL showed the outside lead glass eyewear on left and right sides as 8.06 (0.17–32.45), 3.55(0.06–8.04) mSv and inside left and right sides as 3.91(0.05–14.26) and 2.44(0.06–6.24) mSv respectively.ConclusionEye lens doses measured by OSLD badges and nano Dot dosimeter as Hp(10), Hp(0.07) and Hp(3). The eyes of the IC personnel were examined annually by two ophthalmologists for the prevalence of cataract induced by radiation.     

Split-bolus computed tomography urography (CTU) achieves more than half of radiation dose reduction in females and overweight patients than conventional single-bolus computed tomography urography

ObjectiveTo compare radiation dose between single-bolus and split-bolus computed tomography urography (CTU).Materials and methodsWe prospectively enrolled patients undergoing single-bolus and split-bolus CTU from 2019 June to 2020 June. The age, sex and body mass index (BMI) of each patient was recorded and categorized into BMI classes. The radiation dose indices including volumetric computed dose index, size-specific dose estimate, dose length product and effective dose of each patient were compared between 2 CTU groups with calculation of dose reduction proportions (DRPs).ResultsSeventy-six patients underwent single-bolus (n = 39) and split-bolus (n = 37) CTU. Single-bolus CTU had higher radiation doses than split-bolus CTU and there were statistically significant differences of all radiation dose indices between two CTU groups without and with stratification by sex and BMI classes. The DRPs of volumetric computed dose index, size-specific dose estimate, dose length product and effective dose using split-bolus CTU were 49%, 49%. 50%, and 45%, respectively. Multiple linear regression with an effect size (f²) as 2.24 showed females (p = 0.027) and higher BMI classes (p = 2.38 *10⁻⁹) were associated with higher effective doses; and split-bolus CTU, lower effective doses (p = 5.40 *10⁻¹⁵). Using split-bolus CTU, females had consistently higher DRP of all radiation dose indices than males (54–55% versus 40–42%). Overweight patients had the largest DRP as 55% of effective dose.ConclusionsSplit-bolus CTU could be preferred by its significant radiation dose reduction effect in regard to single-bolus CTU, which was most profound in females and overweight patients.     

Eye lens dose correlations with personal dose equivalent and patient exposure in paediatric interventional cardiology performed with a fluoroscopic biplane system

PurposeTo analyse the correlations between the eye lens dose estimates performed with dosimeters placed next to the eyes of paediatric interventional cardiologists working with a biplane system, the personal dose equivalent measured on the thorax and the patient dose.MethodsThe eye lens dose was estimated in terms of H_p(0.07) on a monthly basis, placing optically stimulated luminescence dosimeters (OSLDs) on goggles. The H_p(0.07) personal dose equivalent was measured over aprons with whole-body OSLDs. Data on patient dose as recorded by the kerma-area product (P_KA) were collected using an automatic dose management system. The 2 paediatric cardiologists working in the facility were involved in the study, and 222 interventions in a 1-year period were evaluated. The ceiling-suspended screen was often disregarded during interventions.ResultsThe annual eye lens doses estimated on goggles were 4.13 ± 0.93 and 4.98 ± 1.28 mSv. Over the aprons, the doses obtained were 10.83 ± 0.99 and 11.97 ± 1.44 mSv. The correlation between the goggles and the apron dose was R² = 0.89, with a ratio of 0.38. The correlation with the patient dose was R² = 0.40, with a ratio of 1.79 μSv Gy⁻¹ cm⁻². The dose per procedure obtained over the aprons was 102 ± 16 μSv, and on goggles 40 ± 9 μSv. The eye lens dose normalized to P_KA was 2.21 ± 0.58 μSv Gy⁻¹ cm⁻².ConclusionsMeasurements of personal dose equivalent over the paediatric cardiologist’s apron are useful to estimate eye lens dose levels if no radiation protection devices are typically used.     

Out-of-field organ doses and associated risk of cancer development following radiation therapy with photons

Innovations in cancer treatment have contributed to the improved survival rate of these patients. Radiotherapy is one of the main options for cancer management nowadays. High doses of ionizing radiation are usually delivered to the tumor site with high energy photon beams. However, the therapeutic radiation exposure may lead to second cancer induction. Moreover, the introduction of intensity-modulated radiation therapy over the last decades has increased the radiation dose to out-of-field organs compared to that from conventional irradiation. The increased organ doses might result in elevated probabilities for developing secondary malignancies to critical organs outside the treatment volume. The organ-specific dosimetry is considered necessary for the theoretical second cancer risk assessment and the proper analysis of data derived from epidemiological reports. This study reviews the methods employed for the measurement and calculation of out-of-field organ doses from exposure to photons and/or neutrons. The strengths and weaknesses of these dosimetric approaches are described in detail. This is followed by a review of the epidemiological data associated with out-of-field cancer risks. Previously published theoretical cancer risk estimates for adult and pediatric patients undergoing radiotherapy with conventional and advanced techniques are presented. The methodology for the theoretical prediction of the probability of carcinogenesis to out-of-field sites and the limitations of this approach are discussed. The article also focuses on the factors affecting the magnitude of the probability for developing radiotherapy-induced malignancies. The restriction of out-of-field doses and risks through the use of different types of shielding equipment is presented.     

Conversion factors for effective dose and organ doses with the air kerma area product in patients undergoing percutaneous transhepatic biliary drainage and trans arterial chemoembolization

Conversion factors used to estimate effective (E) and organ doses (H_T) from air Kerma area product (KAP) are required to estimate population doses in percutaneous transhepatic biliary drainage (PTBD) and trans arterial chemoembolization (TACE) interventional procedures.In this study, E and H_T for ten critical organs/tissues, were derived in 64 PTBD and 48 TACE procedures and in 14,540 irradiation events from dosimetric, technical and geometrical information included in the radiation dose structured report using the PCXMC Monte Carlo model, and the ICRP 103 organ weighting factors. Conversion factors of: 0.13; 0.19; 0.26 and 0.32 mSv Gy⁻¹ cm⁻² were established for irradiation events characterized by a Cu filtration of 0.0; 0.1; 0.4 and 0.9 mm, respectively. While a single coefficient of conversion is not able to provide estimates of E with enough accuracy, a high agreement is obtained between E estimated through Monte Carlo methods and E estimated through E/KAP conversion factors accounting separately for the different modes of fluoroscopy and the fluorography component of the procedures.An algorithm for the estimation of effective and organ doses from KAP has been established in biliary procedures which considers the Cu filtration in the X-ray irradiation events. A similar algorithm could be easily extended to other interventional procedures and incorporated in radiation dose monitoring systems to provide dosimetric estimates automatically with enough accuracy to assess population doses.     

Elimination of biological and physical artifacts in abdomen and brain computed tomography procedures using filtering techniques

IntroductionMedical images are usually affected by biological and physical artifacts or noise, which reduces image quality and hence poses difficulties in visual analysis, interpretation and thus requires higher doses and increased radiographs repetition rate.ObjectivesThis study aims at assessing image quality during CT abdomen and brain examinations using filtering techniques as well as estimating the radiogenic risk associated with CT abdomen and brain examinations.Materials and MethodsThe data were collected from the Radiology Department at Royal Care International (RCI) Hospital, Khartoum, Sudan. The study included 100 abdominal CT images and 100 brain CT images selected from adult patients. Filters applied are namely: Mean filter, Gaussian filter, Median filter and Minimum filter. In this study, image quality after denoising is measured based on the Mean Squared Error (MSE), Peak Signal-to-Noise Ratio (PSNR), and the Structural Similarity Index Metric (SSIM).ResultsThe results show that the images quality parameters become higher after applications of filters. Median filter showed improved image quality as interpreted by the measured parameters: PSNR and SSIM, and it is thus considered as a better filter for removing the noise from all other applied filters.DiscussionThe noise removed by the different filters applied to the CT images resulted in enhancing high quality images thereby effectively revealing the important details of the images without increasing the patients’ risks from higher doses.ConclusionsFiltering and image reconstruction techniques not only reduce the dose and thus the radiation risks, but also enhances high quality imaging which allows better diagnosis.     

Incident air kerma to absorbed organ dose conversion factors for breast and lung in PA thorax radiography: The effect of patient thickness and radiation quality

PurposeConverting the measurable quantities to patient organ doses in projection radiography is usually based on a standard-sized patient model and a specific radiation quality, which are likely to differ from the real situation. Large inaccuracies can therefore be obtained in organ doses, because organ doses are dependent on the exposure parameters, exposure geometry and patient anatomy. In this study, the effect of radiation quality and patient thickness on the organ dose conversion factors were determined.MethodsIn this study, the posterior–anterior projection radiograph of the thorax was selected in order to determine the effect of radiation quality (tube voltages of 70–130 kV and total filtrations of 3 mmAl to 4 mmAl + 0.2 mmCu) and patient thickness (anterior–posterior thicknesses of 19.4–30.8 cm) on the breast and lung dose conversion factors. For this purpose, Monte Carlo simulation programs ImpactMC and PCXMC were used with computed tomography examination data of adult male and female patients and mathematical hermaphrodite phantoms, respectively.ResultsCompared to the reference beam quality and patient thickness, the relative variation range in organ dose conversion factors was up to 74% for different radiation qualities and 122% for different patient thicknesses.ConclusionsConversion factors should only be used with comprehensive understanding of the exposure conditions, considering the exposure parameters, exposure geometry and patient anatomy they are valid for. This study demonstrates that patient thickness-specific and radiation quality-specific conversion factors are needed in projection radiography.     

Normoxic polymer gel dosimetry using less toxic monomer of N-isopropyl acrylamide and X-ray computed tomography for radiation therapy applications

Background

Polymer gel dosimetry has been used extensively in radiation therapy for its capability in depicting a three dimensional view of absorbed dose distribution. However, more studies are required to find less toxic and more efficient polymers for application in radiotherapy dosimetry.

Aim

The purpose of this work was to evaluate the N-isopropyl acrylamide (NIPAM) gel dosimetric characteristics and optimize the protocol for X-ray computed tomography (CT) imaging of gel dosimeters for radiation therapy application.

Material and methods

A polymer gel dosimeter based on NIPAM monomer was prepared and irradiated with ⁶⁰Co photons. The CT number changes following irradiation were extracted from CT images obtained with different sets of imaging parameters.

Results

The results showed the dose sensitivity of ΔN_CT (H) = 0.282 ± 0.018 (H Gy⁻¹) for NIPAM gel dosimeter. The optimized set of imaging exposure parameters was 120 kV_p and 200 mA with the 10 mm slice thickness. Results of the depth dose measurement with gel dosimeter showed a great discrepancy with the actual depth dose data.

Conclusion

According to the current study, NIPAM-based gel dosimetry with X-ray CT imaging needs more technical development and formulation refinement to be used for radiation therapy application.