Conceptus Dose Research Articles

Estimation of patients' organ doses and conceptus doses from selected X-ray examinations in two Nigeria X-ray centres

In this study, organ and conceptus doses of patients undergoing chest, abdomen and skull radiograph examinations at two Nigeria X-ray centres, Niger State General Hospital (NGH) and Two-Tees (TTX), are reported. Air kerma was measured, and entrance surface dose (ESD) and half-value layer estimated for each set of tube potential (kV(p)), focus to skin distance and current-time product (mAs) used for each of the patients included in this study. Results show that the mean air kerma in the two centres are similar for the three projections considered in this study. Organ doses ranged from <0.01 to 2.18 mGy in NGH and from <0.01 to 1.29 mGy in TTX for examinations of the abdomen, from <0.01 to 0.20 mGy in NGH and from <0.01 to 0.13 mGy in TTX for examinations of the skull and from <0.01 to 3.90 mGy in NGH and from <0.01 to 1.96 mGy in TTX for examinations of the chest. Generally, no significant difference is seen between the organ doses of male and female patients. In NGH, organ doses are generally greater than those from TTX for the three examinations. The mean ESDs for examinations of the chest postero-anterior, abdomen antero-posterior (AP) and skull AP are, respectively, 5.37, 6.28 and 4.24 mGy in NGH, and 5.82, 5.33 and 4.76 mGy in TTX. The ESDs reported in this study, except for examinations of the chest, are generally lower than comparable values published in the literature. Conceptus doses were also estimated for female patients using normalised published conceptus dose data for abdomen examinations. The estimated conceptus doses were >1 mGy even when the conceptus was located 12 cm below the surface of the abdomen.

SU‐FF‐I‐48: Normalized Conceptus Doses for Multi‐Detector CT Examinations : A Monte Carlo Study

Purpose: To provide normalized conceptus dose data for the estimation of the conceptus dose from examinations performed using a 16‐slice CT scanner. Method and Materials: The Monte Carlo N‐Particle (MCNP) radiation transport code was employed in this study to model the Siemens Sensation 16 CT scanner. Four mathematical phantoms were used simulating women at 0, 3, 6 and 9 months of gestation. The contribution to the conceptus dose from a single scan was measured at various positions across the phantom. To verify MCNP results, conceptus dose measurements were carried out by means of (a) three physical anthropomorphic phantoms simulating pregnancy at 0, 3 and 6 months of gestation and (b) thermoluminescence dosimetry. The scans were carried out using a Siemens Sensation 16 scanner. Results: The results consist of normalized conceptus dose coefficients for single slices of 2 cm width across the 4 mathematical phantoms. These coefficients were defined as the conceptus dose contribution from a single slice divided by the CTDI free‐in‐air measured with identical scanning parameters. Normalized conceptus dose data were calculated for (a) 120 kV and 140 kV and (b) 12 mm and 24 mm beam collimation. The mean conceptus dose can be calculated using the following formula: urn:x-wiley:00942405:media:mp0425:mp0425-math-0001 where Dc is the dose to the conceptus, CTDIF is the CTDI free‐in‐air, BC is the beam collimation in mm, fz the normalized conceptus dose coefficients and z1, z2 the boundaries of the scanned volume. Taking into account phantom differences, there was a good agreement between the results of the TLD measurements and the mathematical simulation. Conclusion: Accurate estimation of conceptus doses from MDCT examinations performed using a multi‐detector scanner can be made using the dose data provided in this study.

Fluoroscopically Assisted Surgical Treatments of Spinal Disorders: Conceptus Radiation Doses and Risks

A series of anterior-posterior and lateral fluoroscopic exposures at 5 spinal levels were performed on anthropomorphic phantoms simulating the 3 trimesters of gestation. To provide normalized data for the determination of conceptus dose specific to gestational stage and treated spinal level. To estimate the conceptus radiation dose and risk associated with typical fluoroscopically guided spinal treatments performed on the pregnant patient. To our knowledge, there are no available data on conceptus doses and radiogenic risks resulting from fluoroscopically guided spinal surgery of the expectant mother. Direct measurement of conceptus doses from simulated fluoroscopic projections involved in orthopedic surgery at different spinal levels for the 3 trimesters of gestation with use of anthropomorphic phantoms and thermoluminescent dosimetry. Estimation of conceptus radiation risks from a typical pedicle screw fixation and kyphoplasty procedure using the experimentally derived data. Conceptus doses from fluoroscopically guided spinal treatments are smaller than 4 mGy during all gestational stages, provided that the conceptus lies outside the primarily irradiated region. The associated risks of fatal cancer during childhood and congenital malformation on its progeny are at least 2 and 1500 times, respectively, lower than the spontaneous incidence rates. When the embryo is primarily irradiated, mean conceptus dose can be as high as 105 mGy from a nonoptimized exposure. At least 35 minutes of fluoroscopy are required for the induction of deterministic effects. Individual dose assessment is paramount in every pregnancy. Variations in fluoroscopy practices and gestational stage significantly affect fetal doses.

Anticipation of Radiation Dose to the Conceptus from Occupational Exposure of Pregnant Staff During Fluoroscopically Guided Electrophysiological Procedures

Conceptus dose from occupational exposure. A female employee working in the electrophysiology suite has the right to know potential radiation hazards to the unborn child before she is pregnant or before she decides to formally declare her pregnancy. Moreover, the employer of a declared pregnant worker must evaluate the work situation and ensure that the conceptus dose is kept below the maximum permissible level during the remaining gestation period. The aim of this study was to develop a method for conceptus dose anticipation and determination of maximum workload allowed for the pregnant employee who participates in fluoroscopically guided electrophysiological procedures. A C-arm fluoroscopy system, an anthropomorphic phantom, and a radiation meter were used to obtain scattered air kerma dose rates separately for each of the three fluoroscopic projections typically used in the electrophysiology suite. Air kerma to conceptus dose conversion factors for all trimesters of gestation were calculated using Monte Carlo simulation. A formula is presented for the anticipation of the conceptus dose from occupational exposure of pregnant staff during fluoroscopically guided electrophysiological procedures. Normalized data are provided for conceptus dose estimation from occupational exposure of pregnant staff working in any electrophysiology laboratory. A methodology for estimation of maximum workload allowed for each month of the remaining gestation period of a worker who declared her pregnancy is proposed, which ensures that the regulatory dose limits are not exceeded. Data presented may be used for the implementation of a radiation protection program designed for pregnant staff working in an electrophysiological suite.

Determination of Potential Uterine (Conceptus) Doses From Axial and Helical CT Scans

A tissue equivalent Rando Phantom and thermoluminescent dosimeters (TLDs) (LiF) were used to determine potential doses to the uterus at approximately the position of a conceptus from axial and helical CT scans of that region of the body. Doses were measured at the surface of the phantom and at various locations throughout the phantom. The results indicate that measurements taken on the surface of a patient or phantom are generally higher than the level at the location of the uterus within the patient. The results also indicate that the dose to tissue that is 12.7 cm (5 in) out of the direct beam is less than 10% of the dose within the beam. For tissues that are 20 cm (8 in) out of the beam, the dose is approximately 1% of the dose in the beam.

1064 poster Monte Carlo calculated conceptus dose in brain radiotherapy

1064 poster Monte Carlo calculated conceptus dose in brain radiotherapy

When a pregnant woman with suspected appendicitis is referred for a CT scan, what should a radiologist do to minimize potential radiation risks?

Published online: 26 May 2004 Springer-Verlag 2004 When a pregnant woman with suspected appendicitis is referred for a CT scan, what should a radiologist do to minimize potential radiation risks? Evaluation of a patient with suspected appendicitis is a classic situation where radiologists must review what the potential benefits will be, evaluate the potential risks, and modify the procedures to reduce the risks. When ultrasound fails, or is not available, CT becomes the modality of choice because it is fast, reliable, and less susceptible to equivocal error. Conceptus dose depends primarily on the following five factors: (1) kV—increasing the Xray tube voltage from 110 to 140 kV will increase the dose by about 60% (at constant mA); (2) mAs per rotation—the dose is directly proportional to the selected mAs per rotation; (3) patient size—the dose increases as patient size decreases; (4) pitch—doubling the pitch will halve the radiation dose; (5) beam collimation—fine collimation increases the dose owing to oversizing of the beam. For pregnant patients, the radiologist should always limit the scan volume to the necessary anatomy, and dual-pass (with and without contrast) studies should be strictly avoided. Using a step-andscan protocol and terminating the study when the appendix is scanned might be considered, but requires the radiologist to be present to review images as they are collected. Standard techniques for appendicitis in an average adult would likely result in a conceptus dose on the order of 30 mGy or less. At doses of <50 mGy, clinically detectable risks to normal mental and physical development have not been observed [1–3]. For a dose of 30 mGy, the most seriously suspected risks to the conceptus are stochastic risks of radiation-induced neoplasm and genetically heritable reproductive effects. The cancer risk is considered to be most important, and the numerical risk of inducing a cancer is dependent on the dose and perhaps on the gestational age [4, 5]. The best numerical estimate of risk is about one cancer per 500 fetuses exposed to 30 mGy of radiation [2]. While this numerical risk estimate has considerable uncertainty and might be too high, it can serve as useful guidance in directing medical care. The benefit/risk analysis demands that we ask this question: ‘‘Rather than risk one potential cancer, is it better to forego CT in 500 pregnant patients with suspected appendicitis, or is it better to scan all 500 cases and accept the one potential cancer in order to obtain a more certain diagnosis and to direct medical care more confidently?’’ The best way to manage the pregnant patient is to be prepared ahead of time. This includes establishing protocols that appropriately use radiation, performing quality Pediatr Radiol (2004) 34: 589–590 DOI 10.1007/s00247-004-1206-8 QUESTION/ANSWER

Pregnancy and diagnostic X-rays

Diagnostic X-ray examinations are carried out in pregnant patients in clinical practice either accidentally or because of clinical urgency. In these cases, estimation of the risk to the conceptus is of paramount importance. The risk is dependent on the gestational age and the amount of radiation dose absorbed by the conceptus. Under normal operating conditions, conceptus doses from extra-abdominal examinations are lower than 1 mGy. In the case of examinations involving the abdomen or pelvis, doses to the embryo may be considerably higher in comparison with extra-abdominal examinations. In such cases, detailed assessment of dose to the conceptus is necessary. Doses to the unborn child below 100 mGy should not be considered a reason for termination of pregnancy. Counselling the pregnant patient regarding the risks of the diagnostic X-ray examination is essential. Deterministic effects have a threshold of 100 mGy or higher. This dose is higher than that expected from the overwhelming majority of the diagnostic X-ray examinations. As a result of radiation exposure, the conceptus is assumed to be at risk for stochastic effects, mainly childhood cancer, leukaemia and hereditary effects. The risk for radiation-induced childhood fatal cancer is about 6% per Gy. Risk estimates for genetic effects have been estimated to be about 1% per Gy. Pregnant workers are also exposed to diagnostic X-rays. The protection provided for the conceptus of the worker should be comparable to that of the general public (1 mGy) during the declared pregnancy. A radiation protection program for pregnant staff working at diagnostic radiology departments should be implemented to control conceptus exposure and assist the pregnant woman in obtaining the information necessary to continue her job safely.

Conceptus radiation dose assessment from fluoroscopically assisted surgical treatment of hip fractures.

Our aims in the present study were to (a) provide normalized dose data for the estimation of the conceptus dose from fluoroscopically assisted surgical treatment of hip fractures carried out during all trimesters of pregnancy and (b) estimate the conceptus radiation dose and risks associated with fluoroscopy during a typical treatment of hip fracture performed on a pregnant woman. Conceptus doses normalized to entrance surface dose (ESD) or dose area product (DAP) were obtained with the help of anthropomorphic phantoms simulating pregnancy in the three trimesters of gestation. ESD and conceptus dose measurements were carried out using thermoluminescent dosimeters. DAP to conceptus dose conversion factors were estimated for the first, second and third trimesters of gestation. Conceptus dose data normalized to ESD were also estimated to investigate whether these conversion factors may be used for procedures carried out in x-ray units not equipped with a DAP meter. Fluoroscopically assisted surgical treatments were performed in 18 women. The projections involved in these procedures are (a) posteroanterior (PA) and (b) lateral crosstable 45 degrees (LC). Radiation doses for a potential conceptus were estimated by using normalized dose data obtained in phantoms. The results consist of tabulated dose data normalized to DAP or ESD for the estimation of a conceptus dose. An important finding of this study was that the total DAP of a procedure, instead of the individual DAP values of each projection, could be used for the accurate estimation of the conceptus dose. Conceptus doses calculated using dose data normalized to ESD are about 23% higher compared to those estimated using data normalized to DAP. This discrepancy may be attributed to the contribution of scattering radiation from PA projection to ESD measurement of LC projection and vice versa. Therefore, dose data normalized to ESD do not provide accurate conceptus dose estimation. Doses normalized to DAP showed a dependence on (a) tube potential and (b) tube filtration. Data are provided to extent the doses normalized to DAP for the standard spectrum to other tube voltages and filtrations. The maximum dose for a potential conceptus was 0.425 mGy for a patient irradiated for 50 seconds during the PA projection and for 40 seconds during the LC projection. Although the total duration of fluoroscopy is usually less than 2 minutes during a typical procedure, screening time as long as 14 minutes has been reported in the literature for treatment of complex fractures. The relationship between conceptus dose and fluoroscopy time found in the current study showed that, in these cases, the radiation dose received by a conceptus may exceed 1 mGy. In conclusion, an accurate estimation of conceptus doses associated with fluoroscopically assisted surgical treatment of hip fractures can be made using the DAP normalized dose data provided in this study. Conceptus doses from a typical procedure is less than 1 mGy during all trimesters.

Radiation dose to conceptus resulting from tangential breast irradiation

Purpose: To estimate the radiation dose to the conceptus resulting from tangential breast irradiation. Methods and Materials: Conceptus radiation doses were measured in anthropomorphic phantoms simulating the geometry of a pregnant woman at the first, second, and third trimesters of gestation. Medial and lateral field irradiations were generated using a 6-MV X-ray beam. Dose measurements were performed with thermoluminescent dosimeters. Results: For a treatment course delivering 50 Gy to the tumor, conceptus dose at the first trimester of gestation was found to be 2.1–7.6 cGy, depending on the field size used and the distance between conceptus and primary irradiation field. The corresponding dose ranges to the conceptus during the second and third trimesters of gestation were 2.2–24.6 cGy and 2.2–58.6 cGy, respectively. Dose data and formulas are presented to estimate conceptus dose for individual patients undergoing breast radiotherapy during the entire pregnancy. Conclusions: This study may be of value in the management of pregnant women needing tangential breast irradiation, because it provides the required information to estimate conceptus dose.

Conceptus radiation dose and risk from chest screen-film radiography.

The objectives of the present study were to (a) estimate the conceptus radiation dose and risks for pregnant women undergoing posteroanterior and anteroposterior (AP) chest radiographs, (b) study the conceptus dose as a function of chest thickness of the patient undergoing chest radiograph, and (c) investigate the possibility of a conceptus to receive a dose of more than 10 mGy, the level above which specific measurements of conceptus doses may be necessary. Thermoluminescent dosimeters were used for dose measurements in anthropomorphic phantoms simulating pregnancy at the three trimesters of gestation. The effect of chest thickness on conceptus dose and risk was studied by adding slabs of lucite on the anterior and posterior surface of the phantom chest. The conceptus risk for radiation-induced childhood fatal cancer and hereditary effects was calculated based on appropriate risk factors. The average AP chest dimension (d(a)) was estimated for 51 women of childbearing age from chest CT examinations. The value of d(a) was estimated to be 22.3 cm (17.4-27.2 cm). The calculated maximum conceptus dose was 107 x 10(-3) mGy for AP chest radiographs performed during the third trimester of pregnancy with maternal chest thickness of 27.2 cm. This calculation was based on dose data obtained from measurements in the phantoms and d(a) estimated from the patient group. The corresponding average excess of childhood cancer was 10.7 per million patients. The risk for hereditary effects was 1.1 per million births. Radiation dose for a conceptus increases exponentially as chest thickness increases. The conceptus dose at the third trimester is higher than that of the second and first trimesters. The results of the current study suggest that chest radiographs carried out in women at any time during gestation will result in a negligible increase in risk of radiation-induced harmful effects to the unborn child. After a properly performed maternal chest X-ray, there is no need for individual conceptus dose estimations.

Brain radiotherapy during pregnancy: an analysis of conceptus dose using anthropomorphic phantoms.

The aims of this study were: (a) to determine conceptus dose resulting from brain radiotherapy; (b) to investigate the necessity of using shielding devices over patient's abdomen during treatment; and (c) to estimate the components of conceptus dose. Radiation doses received by conceptus were measured using anthropomorphic phantoms simulating pregnancy at 4, 12 and 24 weeks gestation and thermoluminescent dosemeters. All irradiations were performed with two lateral and opposed fields approximating the minimum, medium and maximum field size used during treatment of brain malignancies. For a treatment course delivering 65 Gy to tumour without using shielding equipment, conceptus dose never exceeded 100 mGy. Appropriate positioning of 5.1 cm of lead over the phantom's abdomen provided reduction of conceptus dose from 26% to 71%, depending upon gestational age, field size and distance from the field isocentre. The contribution of scatter arising from within the phantom to the conceptus dose was small compared with that from head leakage and collimator scatter. Our dosimetric results indicate that the construction of special shielding equipment is not a prerequisite for treating brain malignancies during pregnancy. However, based on the concept that exposures in women of childbearing age should be kept as low as reasonably achievable, we suggest that shielding devices should be used whenever possible.

Conceptus dose from two state-of-the-art CT scanners.

Two phantoms, constructed from plastic and water and appropriately proportioned to simulate the female pelvis, were used in the evaluation of the dose delivered to a conceptus from two widely used computed tomographic (CT) scanners. Doses were measured along the central axis and surface of each phantom while scanning 25 contiguous 1-cm sections. Ionization chambers were used for data acquisition. Methods for correcting for partial volume effects inside the chambers are examined. Formulas for calculating the dose to the conceptus in a wide variety of possible situations are presented. These data may be used to guide management of pregnant patients who require or have had CT examinations.

Pregnancy and women radiologists.

Concerns about conceptus exposure to ionizing radiation, the level of conceptus dose that is likely to result from the mother's occupation, precautions to insure low conceptus dose, and the effects of radiation on the conceptus are discussed as they relate to the woman radiologist, her career and possible pregnancy. The amounts of radiation per examination are tabulated for the various radiologic modalities, and a summary is given of exposure levels.