Fetal Dose Research Articles

Fetal exposure to mercury and lead from intrauterine blood transfusions.

Mercury (Hg) and lead (Pb) exposure during childhood is associated with irreversible neurodevelopmental effects. Fetal exposure to Hg and Pb from intrauterine blood transfusion (IUBT) has not been reported. Fetal exposure was estimated based on transfusion volume and metal concentration in donor packed red blood cell (PRBCs). As biomarkers to quantify prenatal exposure are unknown, Hg and Pb in donor PRBCs were compared to estimated intravenous (IV) RfDs based on gastrointestinal absorption. Three pregnant women received 8 single-donor IUBTs with volumes ranging from 19 to 120 mL/kg. Hg and Pb were present in all donor PRBC units. In all, 1/8 IUBT resulted in Hg dose five times higher than the estimated IV RfD. Median Pb dose in one fetus who received 5 single-donor IUBTs between 20-32 weeks gestation was 3.4 μg/kg (range 0.5-7.9 μg/kg). One donor unit contained 12.9 μg/dL of Pb, resulting in a fetal dose of 7.9 μg/kg, 40 times higher than the estimated IV RfD at 20 weeks gestation. This is the first study documenting inadvertent exposure to Hg and Pb from IUBT and quantifying the magnitude of exposure. Screening of donor blood is warranted to prevent toxic effects from Hg and Pb to the developing fetus.

18F-FDG Whole-body PET/MRI of a 30-Week Pregnant Woman With Breast Cancer Revealed Interesting Fetal Findings

A 35-year-old 30-week pregnant woman was referred to our institution for initial staging of a triple negative invasive ductal carcinoma of the left breast. To avoid fetal radiation exposure from CT, a whole-body F-FDG PET/MRI was performed. Simultaneous acquisition of PET, T1-, T2-, and diffusion-weighted sequences revealed left axillary node extension and no distant metastases. Fetal radiation dose was estimated at 1.9 mGy. Interestingly, low fetal brain uptake and high symmetrical myocardial metabolism in both ventricles were found. Delivery was induced at 37 weeks of amenorrhea, and the patient underwent 4 cycles of neoadjuvant chemotherapy.

Intra- and inter-rater reliability in a comparative study of cross-sectional and spiral computed tomography pelvimetry methods.

BackgroundDifferent low-dose computed tomography (CT) pelvimetry methods can be used to evaluate the size of birth canal before delivery. CT pelvimetry might generate an acceptable low fetal radiation dose but its measurement accuracy is unknown.PurposeTo investigate intra- and inter-rater measurement reliability of cross-sectional and two spiral CT pelvimetry methods: standard spiral and short spiral.Material and MethodsTen individuals (age ≥60 years, body mass index ≥30 kg/m2) having a CT scan of the abdomen also had CT pelvimetry scans. Three radiologists made independent measurements of each pelvimetry method on two occasions and also in consensus for a reference pelvimetry computed from the standard-dose CT scan of the abdomen. Inter- and intra-rater reliability was analyzed by intraclass correlation coefficient.ResultsMeasurements in the short spiral pelvimetry demonstrated excellent intra- and inter-rater reliability, intraclass correlation coefficient ≥0.93, and good to excellent 95% confidence interval 0.87–0.99. Corresponding results of the standard spiral and cross-sectional pelvimetry showed good to excellent intraclass correlation coefficient ≥0.85 and ≥0.76, and 95% confidence interval was least good and moderate 0.73–0.98 and 0.59–0.97, respectively. Intraclass correlation coefficient between reference pelvimetry and other CT methods showed analogous results.ConclusionThe short spiral pelvimetry demonstrated high and best reliability in comparison to other methods. Standard spiral method showed also good measurement reliability but the short spiral pelvimetry generates lower fetal radiation dose. This method might be suitable for measurements at narrow pelvis. Patient acceptance and attitude to CT pelvimetry should be investigated.

Applying radiation protection and safety in radiotherapy.

Radiotherapy is one of the primary treatment options in cancer management. Modern radiotherapy includes complex processes requiring many different kinds of expertise. Among them, knowledge and skills are needed in clinical oncology, radiobiology, radiotherapy planning and simulation, dose measurement and calculation, radiation safety and medical physics. Radiation oncologists should assume the full and final responsibility for treatment, follow-up and supportive care of the patient. For all these activities, radiation oncologist should coordinate and collaborate with a team including different professionals: nurses, radiographers (RTT), clinical engineers, information system experts, taking advantage in particular of the dosimetry expertise of the medical physicist. Radiation therapy is widely recognized to be one of the safest areas of modern medicine, and errors are very rare. However, radiation protection recommendations developed at national level should comply with the EURATOM Directive 2013/59. This paper describes several contemporary and emerging concerns related to radioprotection in radiation therapy including quality and safety in external beam radiotherapy and brachytherapy, foetal dose, secondary malignancies, and the safety issues related to the new techniques and treatment strategies.

Estimating fetal dose from tube current-modulated (TCM) and fixed tube current (FTC) abdominal/pelvis CT examinations.

The purpose of this work was to estimate scanner-independent CTDIvol -to-fetal-dose coefficients for tube current-modulated (TCM) and fixed tube current (FTC) computed tomography (CT) examinations of pregnant patients of various gestational ages undergoing abdominal/pelvic CT examinations. For 24 pregnant patients of gestational age from <5 to 36weeks who underwent clinically indicated CT examinations, voxelized models of maternal and fetal (or embryo) anatomy were created from abdominal/pelvic image data. Absolute fetal dose (Dfetus ) was estimated using Monte Carlo (MC) simulations of helical scans covering the abdomen and pelvis for TCM and FTC scans. Estimated TCM schemes were generated for each patient model using a validated method that accounts for patient attenuation and scanner output limits for one scanner model and were incorporated into MC simulations. FTC scans were also simulated for each patient model with multidetector row CT scanners from four manufacturers. Normalized fetal dose estimates, nDfetus , was obtained by dividing Dfetus from the MC simulations by CTDIvol . Patient size was described using water equivalent diameter (Dw ) measured at the three-dimensional geometric centroid of the fetus. Fetal depth (DEf ) was measured from the anterior skin surface to the anterior part of the fetus. nDfetus and Dw were correlated using an exponential model to develop equations for fetal dose conversion coefficients for TCM and FTC abdominal/pelvic CT examinations. Additionally, bivariate linear regression was performed to analyze the correlation of nDfetus with Dw and fetal depth (DEf ). For one scanner model, nDfetus from TCM was compared to FTC and the size-specific dose estimate (SSDE) conversion coefficients (f-factors) from American Association of Physicists in Medicine (AAPM) Report 204. nDfetus from FTC simulations was averaged across all scanners for each patient . was then compared with SSDE f-factors and correlated with Dw using an exponential model and with Dw and DEf using a bivariate linear model. For TCM, the coefficient of determination (R2 ) of nDfetus and Dw was observed to be 0.73 using an exponential model. Using the bivariate linear model with Dw and DEf , an R2 of 0.78 was observed. For the TCM technology modeled, TCM yielded nDfetus values that were on average 6% and 17% higher relative to FTC and SSDE f-factors, respectively. For FTC, the R2 of with respect to Dw was observed to be 0.64 using an exponential model. Using the bivariate linear model, an R2 of 0.75 was observed for with respect to Dw and DEf . A mean difference of 0.4% was observed between and SSDE f-factors. Good correlations were observed for nDfetus from TCM and FTC scans using either an exponential model with Dw or a bivariate linear model with both Dw and DEf . These results indicate that fetal dose from abdomen/pelvis CT examinations of pregnant patients of various gestational ages may be reasonably estimated with models that include (a) scanner-reported CTDIvol and (b) Dw as a patient size metric, in addition to (c) DEf if available. These results also suggest that SSDE f-factors may provide a reasonable (within ±25%) estimate of nDfetus for TCM and FTC abdomen/pelvis CT exams.

Diagnostic imaging in pregnancy: Making informed decisions.

The use of diagnostic imaging involving ionising radiation may be necessary in pregnancy and requires an assessment of the most appropriate and safest imaging modality which will provide the necessary information balanced with the potential risks to the mother and fetus. In most cases, this will involve a potential fetal radiation dose well below 50 mGy. At these doses, there is no risk of lethality, genetic damage/epigenetic change, teratogenicity, growth impairment or sterility. Older epidemiological data indicating a potential increased cancer risk have been contradicted by newer data and better understanding of the biology of low dose radiation. The linear no-threshold rule has been challenged by many and more realistic estimates of oncogenicity risk along with the potential risks of contrast agents are summarised in this review. Imaging in the pregnant population is increasing in both the number of examinations performed and the number of patients being imaged, with the greatest increase being computed tomography scans. Counselling and obtaining informed consent for imaging that involves radiation requires the clinician to communicate with the woman and her family a realistic estimate of the potential radiation dose to herself and her fetus, to describe and quantitate the risks of this estimated dose, to outline the benefits of the imaging procedure and to respond to any questions or concerns. As almost all diagnostic imaging involves doses below the 50 mGy threshold, clinically indicated investigations should not be withheld during pregnancy. All allied staff must also be well informed to ensure the patient receives a consistent message about the risks and benefits of the proposed test.

EP-1682 Fetal dose from head and neck tomotherapy versus 3D conformal radiotherapy

EP-1682 Fetal dose from head and neck tomotherapy versus 3D conformal radiotherapy

The OPTICA study (Optimised Computed Tomography Pulmonary Angiography in Pregnancy Quality and Safety study): Rationale and design of a prospective trial assessing the quality and safety of an optimised CTPA protocol in pregnancy

BackgroundCTPA is the gold standard investigation for evaluating suspected pulmonary embolism (PE) in the general population however is sometimes considered second line in pregnant and post-partum patients with a normal CXR due to its higher breast dose and the increased radio-sensitivity of breast tissue during this period. Guidelines advocating for scintigraphy over CTPA, however, quote significantly higher breast doses than those achievable with optimised low dose strategies. Defining the radiation dose achievable with a specific low-dose CTPA protocol is therefore imperative. As decreasing dose is associated with increased image noise, demonstrating the image quality and validity of a negative low-dose CTPA in out-ruling PE in this population is necessary. MethodsThe OPTICA study is a prospective multicentre observational study aiming to validate the clinical utility and safety of an optimised low-dose CTPA protocol in pregnancy. An optimised low-dose CTPA protocol has been agreed across all study sites with equivalent CT capabilities. Pregnant women undergoing CTPA for suspected PE will be included. Independent review of CTPAs by two radiology consultants, image data analysis and 3-month patient follow up will be performed. The primary outcome is the 3-month incidence of VTE in pregnant patients in whom PE was excluded at baseline CTPA. Secondary outcomes will confirm the associated radiation dose and image quality of this protocol. The radiation dose will be calculated using the Monte Carlo method and will include maternal effective, breast and foetal doses. Image quality will be assessed objectively by measuring opacification of the main pulmonary trunk, signal-to-noise and contrast-to-noise ratios and subjectively using a grading scale and inter-reader variability of CTPA results. ConclusionThe OPTICA study is the first prospective trial of a low-dose CTPA protocol in the pregnant population. It will provide high-quality evidence defining the achievable dose, image quality and safety of an optimised CTPA for this population. It will assist other institutes with similar CT capabilities in achieving comparable low doses for its patients and provide an evidence base upon which modern CTPA protocols can be appropriately compared to scintigraphy in the pregnant population.

Foetal radiation exposure caused by mechanical thrombectomy in large-vessel ischaemic stroke in pregnancy.

There is overwhelming evidence for the clinical benefits that are derived following mechanical thrombectomy in large-vessel acute ischaemic stroke. The risk of stroke is elevated in pregnancy due to many factors. To date, there have been two reports, totalling five patients, who have undergone mechanical thrombectomy in pregnancy, thus demonstrating the feasibility of the procedure; however, there is no data on the radiation exposure to the mother or foetus related to this therapy. We highlight the important technical considerations to minimise the risk of the procedure and report the estimated dose received by mother and foetus. We also compare these doses with those received during whole-body CT in trauma and CT pulmonary angiogram (CTPA) examinations. Three cases of mechanical thrombectomy were performed at separate tertiary referral neuroscience centres in the UK. Following diagnostic CT and mechanical thrombectomy, the total whole-body effective dose to the pregnant patient was significantly higher than in patients undergoing CTPA (p< 0.05), but not significant different compared to whole-body CT imaging in trauma patients. The estimated dose received by the foetus following diagnostic CT and mechanical thrombectomy was significantly lower than in whole-body imaging in trauma patients at p< 0.05, with no difference in estimated foetal dose compared to CTPA imaging. The estimated doses received by the foetus during diagnostic stroke imaging and mechanical thrombectomy are equivalent to, or less than, purely diagnostic imaging in emergency situations.

Computed Tomography Pulmonary Angiography during Pregnancy: Radiation Dose of Commonly Used Protocols and the Effect of Scan Length Optimization.

ObjectiveTo evaluate the radiation dose for pregnant women and fetuses undergoing commonly used computed tomography of the pulmonary arteries (CTPA) scan protocols and subsequently evaluate the simulated effect of an optimized scan length.Materials and MethodsA total of 120 CTPA datasets were acquired using four distinctive scan protocols, with 30 patients per protocol. These datasets were mapped to Cristy phantoms in order to simulate pregnancy and to assess the effect of an effective radiation dose (in mSv) in the first, second, or third trimester of pregnancy, including a simulation of fetal dose in second and third trimesters. The investigated scan protocols involved a 64-slice helical scan at 120 kVp, a high-pitch dual source acquisition at 100 kVp, a dual-energy acquisition at 80/140 kVp, and an automated-kV-selection, high pitch helical scan at a reference kV of 100 kVref. The effective dose for women and fetuses was simulated before and after scan length adaptation. The original images were interpreted before and after scan length adaptations to evaluate potentially missed diagnoses.ResultsLarge inter-scanner and inter-protocol variations were found; application of the latest technology decreased the dose for non-pregnant women by 69% (7.0–2.2 mSv). Individual scan length optimization proved safe and effective, decreasing the fetal dose by 76–83%. Nineteen (16%) cases of pulmonary embolism were diagnosed and, after scan length optimization, none were missed.ConclusionCareful CTPA scan protocol selection and additional optimization of scan length may result in significant radiation dose reduction for a pregnant patient and her fetus, whilst maintaining diagnostic confidence.

Radiation exposure during pelvimetry CT procedures in Ibn Sina Children's Hospital of Rabat

PurposeThe goal of this pilot study was to estimate the doses delivered during of pelvimetry Computed Tomography (CT) procedures in order to establish local diagnostic reference level (DRL) of Ibn Sina Children's Hospital of Rabat. Materials and methodsThis study consisted of examining a total of 30 patients. All CT examinations were performed with a SIEMENS Somatom Sensation 64 CT with Automatic Exposure Control System. The data that collected for each diagnostic exam chosen included scanner acquisition parameters, number of series, use of the contrast medium, and rotation time as well as slice thickness, the displayed CT dose index (CTDIvol) and the Dose Length Product (DLP). Effective dose and DRL were evaluated using the International Commission on Radiological Protection (ICRP) conversion factor. ResultsThe average age of women who have benefited from the pelvimetry CT scan is equal to 25.10 ± 4.75 years. Tube voltage (kV), tube current and rotation time were 110 (kV), 30 (mA) and 0,8 (s) respectively. The average displayed CT dose index CTDIvol were 2.15 ± 0.02 mGy. The average dose length product (DLP) was (55.97 ± 0.25) mGy cm. The average effective dose received by women pregnant during a pelvimetry CT scan was 0.84 ± 0.01 mSv. The foetal dose was 2.36 ± 0.02 mGy. The local DRL for this procedure was equal to 56.66 ± 2.15 mGy cm. ConclusionOur values are higher than the standards of some European countries. This first ever survey of CT practice in Ibn Sina Children's Hospital of Rabat confirmed the need to improved training of health professionals involved in computed tomography on factors affecting image quality and dose and protocols optimization.

Pregnancy outcome after first trimester exposure to ionizing radiations

ObjectiveTo evaluate the effects of ionizing radiation exposure during the first trimester of pregnancy in usual clinical situations. Study designWe conducted a prospective observational cohort study using data collected between 1987 and 2014. This database was authorized by the French “Commission Nationale de l’Informatique et des Libertés”. The exposed group consisted of 319 pregnant women exposed to sub diaphragmatic ionizing radiations for diagnostic purposes, during the first trimester of pregnancy, and the control group consisted of 319 pregnant women without any exposure or exposed to non-teratogenic agents. Data on maternal history and radiations exposure were collected on first contact, and pregnancy outcomes were documented at follow-up. An univariate analysis was performed to compare both groups for the main outcomes. ResultsExposure to sub diaphragmatic ionizing radiation for diagnosis purpose (median fetal dose of 3.1 mGy [0.2–130.0]) during the first trimester of pregnancy was not significantly associated with an increased risk of malformations (1.5% vs 1.8%, p = 1.00), miscarriage (7.8% vs 7.2%, p = 0.88), in utero fetal death (0.3% vs 0%, p = 1.00) or fetal growth restriction (5.4% vs 3.5%, p = 0.62). ConclusionPregnant women exposed to irradiant diagnostic procedures do not present a higher risk of malformations, miscarriage, in utero fetal death or fetal growth restriction and should be reassured, even if the examination focused on the pelvis.

Occupational and patient radiation doses in a modern cardiac electrophysiology laboratory.

Technological advancements have greatly expanded the field of cardiac electrophysiology, requiring greater demands on imaging systems and potentially delivering higher radiation doses to patients and operators. With little contemporary research on occupational and patient radiation risk in the electrophysiology laboratory, the aim of this study was to analyze radiation doses, including occupational fetal doses, over approximately the last decade. We benchmarked the occupational data to our patient radiation dose data to allow for comparison and to put into perspective the associated radiation risks. Occupational radiation dosimetry analyzed included data from an 11-year period for physicians, a 7-year period for nurses, and a 9-year period for fetal doses. Patient-related dose metrics over an 8-year period were also analyzed. In the physician and nursing groups, there was a nearly 70% decrease in the average occupationalradiation doses over the given periods. Within the electrophysiology department, the average fetal occupationaldoses were very low, close to 0μSv. The average reference point air kerma per patient for all electrophysiology procedures decreased from nearly 600mGy/procedure in 2010 to just over 100mGy/procedure in 2017. Patient and occupational radiation doses in our laboratories significantly decreased over the periods analyzed as a result of clinical and technical staff efforts as well as advances in imaging technology. The radiation-related risk to individuals working in our electrophysiology laboratories, including pregnant women, is very low. Data reported herein could be used by other institutions to evaluate their occupational and patient radiation safety practices.

Bisphenol S instead of Bisphenol A: Toxicokinetic investigations in the ovine materno-feto-placental unit

Bisphenol S (BPS) is widely used as a substitute for Bisphenol A in consumer products. Despite its potential endocrine-disrupting effects and widespread exposure, toxicokinetic data, particularly during the critical period of pregnancy, are not available for BPS. The objectives of our study were to evaluate the mechanisms determining fetal exposure to BPS and to BPS glucuronide (BPSG) and to compare them with those prevailing for BPA.The disposition of BPS and BPSG was evaluated in the materno-fetal unit of the catheterized pregnant ewe model, following intravenous administrations of BPS and BPSG to mothers and their fetuses. In a second experiment, the rate of BPS accumulation in the fetal compartment was determined under steady-state conditions after repeated intravenous BPS administrations to the mother.In the maternal compartment, BPS was mainly metabolized into BPSG and totally eliminated in urine. Only 0.40% of the maternal dose was transferred to the fetus. However, once in the fetal compartment, 26% of the fetal dose was rapidly eliminated through placental transfer, while 46% of BPS was metabolized into BPSG which remained trapped in the fetal compartment. Thus, the elimination of BPSG from the fetal compartment required its back-conversion into bioactive BPS, leading to an 87% enhancement of the fetal BPS exposure.Our findings demonstrate that, despite the low materno-fetal placental transfer of BPS, this substitute for BPA is able to accumulate in the fetal compartment after repeated maternal exposure, leading to chronic fetal exposure to BPS in a range of concentrations similar to those of BPA.

Computed tomography pulmonary angiography versus ventilation-perfusion lung scanning for diagnosing pulmonary embolism during pregnancy: a systematic review and meta-analysis.

Differences between computed tomography pulmonary angiography and ventilation-perfusion lung scanning in pregnant patients with suspected acute pulmonary embolism are not well-known, leading to ongoing debate on which test to choose. We searched in PubMed, EMBASE, Web of Science and the Cochrane Library databases and identified all relevant articles and abstracts published up to October 1, 2017. We assessed diagnostic efficiency, frequency of non-diagnostic results and maternal and fetal exposure to radiation exposure. We included 13 studies for the diagnostic efficiency analysis, 30 for the analysis of non-diagnostic results and 22 for the radiation exposure analysis. The pooled rate of false negative test results was 0% for both imaging strategies with overlapping confidence intervals. The pooled rates of non-diagnostic results with computed tomography pulmonary angiography and ventilation-perfusion lung scans were 12% (95% confidence interval: 8-17) and 14% (95% confidence interval: 10-18), respectively. Reported maternal and fetal radiation exposure doses were well below the safety threshold, but could not be compared between the two diagnostic methods given the lack of high quality data. Both imaging tests seem equally safe to rule out pulmonary embolism in pregnancy. We found no significant differences in efficiency and radiation exposures between computed tomography pulmonary angiography and ventilation-perfusion lung scanning although direct comparisons were not possible.

I068] Radiation effects on the embryo and fetus

The effects of in utero radiation should not be confused with heritable effects that can manifest by irradiating germ cells (oocytes or spermatocytes) before conception, causing chromosomal aberrations and/or mutations in the genes themselves. These (stochastic) genetic effects have been documented in animals and insects, but there is no epidemiological evidence of excess heritable disease in the offspring of humans irradiated before conception. The irradiation of somatic cells of the embryo/fetus can cause both tissue injuries and stochastic effects. Tissue injuries are dependent on the fetal stage of development and have been documented in irradiated cohorts of Hiroshima/Nagasaki atomic bomb survivors and residents around Chernobyl and the Mayak Plant/Techa River in the Southern Urals, as well as after medical radiation. According to the 2013 US National Council on Radiation Protection and Measurements Report 174, embryo lethality can occur in the pre-implantation period at doses above 100 mGy; malformations (such as microcephaly, micrognathia and cleft palate) may occur during organogenesis above 100 mGy, and severe mental retardation, in the weeks 8–25th post conception, with a dose threshold of 300 mGy. The most sensitive period is the 8–15th week, where a decrease of up to 30 IQ units has been observed. As for radiation-induced stochastic effects, although cancer has been observed for in utero irradiated cohorts from Hiroshima/Nagasaki and Southern Urals, the numbers are small; it is not known which are the most vulnerable gestation periods. However, the cancer life time risk seems lower than that following irradiation during childhood, which in turn is much higher than in adults. On a mechanistic basis, the 2015 International Commission on Radiological Protection Report 131, suggested that because of high competition between the irradiated and non-irradiated stem cells after low doses in utero, the injured stem cells are discarded before birth, thus yielding a low cancer risk. During childhood growth, stem cell competition is less stringent (higher risk) as the stem cell/niche units increase in number to cope with the increase in tissue volume, an unnecessary mechanism in adulthood (lower risk). The presentation will end showing typical fetal doses in medical radiation procedures.

Radiation treatment planning and delivery strategies for a pregnant brain tumor patient.

The management of a pregnant patient in radiation oncology is an infrequent event requiring careful consideration by both the physician and physicist. The aim of this manuscript was to highlight treatment planning techniques and detail measurements of fetal dose for a pregnant patient recently requiring treatment for a brain cancer. A 27‐year‐old woman was treated during gestational weeks 19–25 for a resected grade 3 astrocytoma to 50.4 Gy in 28 fractions, followed by an additional 9 Gy boost in five fractions. Four potential plans were developed for the patient: a 6 MV 3D‐conformal treatment plan with enhanced dynamic wedges, a 6 MV step‐and‐shoot (SnS) intensity‐modulated radiation therapy (IMRT) plan, an unflattened 6 MV SnS IMRT plan, and an Accuray TomoTherapy HDA helical IMRT treatment plan. All treatment plans used strategies to reduce peripheral dose. Fetal dose was estimated for each treatment plan using available literature references, and measurements were made using thermoluminescent dosimeters (TLDs) and an ionization chamber with an anthropomorphic phantom. TLD measurements from a full‐course radiation delivery ranged from 1.0 to 1.6 cGy for the 3D‐conformal treatment plan, from 1.0 to 1.5 cGy for the 6 MV SnS IMRT plan, from 0.6 to 1.0 cGy for the unflattened 6 MV SnS IMRT plan, and from 1.9 to 2.6 cGy for the TomoTherapy treatment plan. The unflattened 6 MV SnS IMRT treatment plan was selected for treatment for this particular patient, though the fetal doses from all treatment plans were deemed acceptable. The cumulative dose to the patient's unshielded fetus is estimated to be 1.0 cGy at most. The planning technique and distance between the treatment target and fetus both contributed to this relatively low fetal dose. Relevant treatment planning strategies and treatment delivery considerations are discussed to aid radiation oncologists and medical physicists in the management of pregnant patients.

Estimation of foetal radiation dose in a comparative study of pelvimetry with conventional radiography and different computer tomography methods

Introduction Conventional radiography and computed tomography CT can result in different radiation doses to the foetus when pelvimetry needs to be performed before childbirth New techniques in diagnostic imaging provide the basis for the optimization of radiation dose and create opportunities for higher measurement accuracy The purpose of the study was to estimate the radiation dose to the foetus from pelvimetry performed using conventional radiography compared to different CT methods namely the topogram method cross sectional method short spiral method standard spiral method and flash spiral method Methods An anthropomorphic phantom and thermoluminescent dosemeters TLD were used for the dose measurements Bags with sodium chloride were placed on top of the phantom rsquo s abdomen and were used to simulate the last month of pregnancy The foetal radiation dose was equated to the absorbed energy to the TLDs placed at the area of the birth canal uterus Results Themean absorbed dose to the foetus was measured with conventional radiographic technique to mGy The mean absorbed dose to the foetus with the various CT methods resulted in mGy topogram mGy cross sectional mGy short spiral mGy standard spiral and mGy flash spiral Conclusion Although the absorbed dose to the foetus was higher in the CT pelvimetry methods the dose levels are low The CT spiral methods allowed adjustments in multiplane image reconstructions which could increase measurement accuracy However further studies are needed to investigate different CT pelvimetry methods in relation to measurement accuracy

Dosimetric factors for diagnostic nuclear medicine procedures in a non-reference pregnant phantom

This study evaluates the impact of using non-reference fetal models on the fetal radiation dose from diagnostic radionuclide administration. The six-month pregnant phantoms including fetal models at the 10th and 90th growth percentiles were constructed at either end of the normal range around the 50th percentile and implemented in the Monte Carlo N-Particle code version MCNPX 2.6. This code has then been used to evaluate the 99mTc S factors of the target organs of interest, as this is the most commonly used radionuclide in nuclear medicine procedures. Substantial variations were observed in the S factors between the 10th/90th percentile phantoms from the 50th percentile phantom, with the greatest difference being 38.6%. When the source organs were in close proximity to, or inside the fetal body, the 99mTc S factors presented strong statistical correlations with fetal body habitus. The trends observed in the S factors and the differences between various percentiles were justified by the source organs’ masses, and chord length distributions. The results of this study showed that fetal body habitus had a considerable effect on fetal dose (on average up to 8.4%) if constant fetal biokinetic data were considered for all fetal weight percentiles. However, a smaller variation on fetal dose (up to 5.3%) was obtained if the available biokinetic data for the reference fetus were scaled by fetal mass.

The use of out-of-plane high Z patient shielding for fetal dose reduction in computed tomography: Literature review and comparison with Monte-Carlo calculations of an alternative optimisation technique

When performing CT examinations on pregnant patients, great effort should be dedicated towards optimising the exposure of the mother and the conceptus. For this purpose, many radiology departments use high-Z garments to be wrapped around the patient's lower abdomen for out-of-plane organ shielding to protect the fetus. To assess their current protection efficiency, we performed a literature review and compared the efficiencies mentioned in the literature to Monte-Carlo calculations of CT protocols for which the overall scan length was reduced. We found 11 relevant articles, all of them reporting uterus exposure due to CT imaging performed for exclusion of pulmonary embolism, one of the leading causes of peripartum deaths in western countries. Uterus doses ranged between 60 and 660 µGy per examination, and relative dose reductions to the uterus due to high-Z garments were between 20 and 56%. Calculations showed that reducing the scan length by one to three centimetres could potentially reduce uterus dose up to 24% for chest imaging, and even 47% for upper abdominal imaging. These dose reductions were in the order of those achieved by high-Z garments. However, using the latter may negatively influence the diagnostic image quality and even interfere with the automatic exposure control system thus increasing patient dose if positioned in the primary beam, for example in the overranging length in helical acquisition. We conclude that efforts should be concentrated on positioning the patient correctly in the gantry and optimising protocol parameters, rather than using high-Z garments for out-of-plane uterus shielding.