Computed tomography dosimetry with high-resolution detectors commonly used in radiotherapy - an energy dependence study.

New methods of dosimetry in computed tomography (CT) X-ray fields require the use of high-resolution detectors instead of pencil-type ionization chambers typically used for CT dose index (CTDI) measurements. This paper presents a study on the suitability of a wide range of ionization chambers, diodes, and a two-dimensional detector array, used primarily in radiation therapy, for CT and cone-beam CT dosimetry. Specifically, the energy dependence of these detectors from 50 kVp up to 125 kVp is reported. All measurements were performed in reference to a calibrated diode for use in this energy region. The radiation quality correction factors provided by the manufacturer were used, depending on the measured half-value layer (HVL) for the particular X-ray beam. Our study demonstrated the general usability of thimble ionization chambers. These thimble ionization chambers showed a maximum variation in energy response of 5%. Ionization chambers with even smaller sensitive volume, and which exhibit similar variation in energy dependence, can be used if higher spatial resolution is required. Furthermore, the investigated detectors are better suited for dosimetry at CT and CBCT units than conventional large volume or flat detectors, due to their rotational symmetry. Nevertheless, a flat detector can be used for certain measurement tasks, such as the acquisition of percent depth-dose curves or beam profiles for nonrotating beams, which are important for beam characterization.

Tables for effective dose assessment from diagnostic radiology (period 1946-1995) in epidemiologic studies.

Diagnostic radiology is a leading cause of man-made radiation exposure to the population. It is an important factor in many epidemiological studies as variable of interest or as potential confounder. The effective dose as a risk related quantity is the most often stated patient dose. Nevertheless, there exists no comprehensive quantification model for retrospective analysis for this quantity. This paper gives a catalog of effective dose values for common and rare examinations and demonstrates how to modify the dose values to adapt them to different calendar years using a quantification concept already used for retrospective analysis of the red bone marrow dose. It covers the time period of 1946 to 1995 and allows considering technical development and different practical standards over time. For an individual dose assessment, if the dose area product is known, factors are given for most examinations to convert the dose area product into the effective dose. Additionally factors are stated for converting the effective dose into the red bone marrow dose or vice versa.

Radiation Protection in Interventional Radiology/Cardiology-Is State-of-the-Art Equipment Used?

Interventional radiology/cardiology is one of the fields with the highest radiation doses for workers. For this reason, the International Commission on Radiological Protection (ICRP) published new recommendations in 2018 to shield staff from radiation. This study sets out to establish the extent to which these recommendations are observed in Germany. For the study, areas were selected which are known to have relatively high radiation exposure along with good conditions for radiological protection-interventional cardiology, radiology and vascular surgery. The study was advertised with the aid of an information flyer which was distributed via organisations including the German Cardiac Society (Deutsche Gesellschaft für Kardiologie- Herz- und Kreislaufforschung e. V.). Everyone who participated in our study received a questionnaire to record their occupational medical history, dosimetry, working practices, existing interventional installations and personal protective equipment. The results were compared with international recommendations, especially those of the ICRP, based on state-of-the-art equipment. A total of 104 respondents from eight German clinics took part in the survey. Four participants had been medically diagnosed with cataracts. None of the participants had previously worn an additional dosimeter over their apron to determine partial-body doses. The interventional installations recommended by the ICRP have not been fitted in all examination rooms and, where they have been put in place, they are not always used consistently. Just 31 participants (36.6%) stated that they "always" wore protective lead glasses or a visor. This study revealed considerable deficits in radiological protection-especially in connection with shielding measures and dosimetric practices pertaining to the head and neck-during a range of interventions. Examination rooms without the recommended interventional installations should be upgraded in the future. According to the principle of dose minimization, there is considerable potential for improving radiation protection. Temporary measurements should be taken over the apron to determine the organ-specific equivalent dose to the lens of the eye and the head.

[Gender-specific calculation of the effective dose with an example of thoracic CT tomography]. / Geschlechtsspezifische Bestimmung der effektiven Dosis am Beispiel von CT-Thoraxuntersuchungen.

Systematic gender-specific differences in anatomy and physiology are mostly neglected in standard methodologies for the determination of effective doses. This paper presents and discusses three different concepts for the derivation of gender-specific effective doses. Based on the most convincing approach--especially through the influence of tissue weighting factors for the breast--the effective dose for a serial CT scan of the chest is higher for women (+11%) and lower (-11%) for men in comparison to the "gender-neutral" average value. These differences amount to +/- 30% for coronary serial CT applications.

[Radiation exposure to personnel in cardiac catheterization laboratories]. / Strahlenexposition des Personals im Herzkatheterlabor.

Radiation exposure in personnel of cardiac catheterization units is based on local dosimetry during patient investigations. In the present study, dose rates were measured at various heights in representative locations, with and without fixed radiation protection shields in place. To determine the effective dose values, TLD measurements were performed using on Alderson phantom to generate radiation scatter and a second phantom in the position of the cardiologist performing the catheterization. Various types of personal radiation protection garment and fixed shields were considered in the calculations. Our results indicate on one hand that good protective standards can be achieved with effective doses below 1 mSv/year under optimized conditions. On the other hand, inappropriate radiation protection equipment can cause substantial increase of radiation doses. Alone the lack of a thyroid shield increases the effective dose of the cardiologist by a factor of 3. For the personnel, effective doses were generally higher than personal doses by a factor between 1.5 and 4.8 depending on the radiation protection situation.

Influence of age, sex and calendar year on lifetime accumulated red bone marrow dose from diagnostic radiation exposure.

Our aim is to evaluate the relevance of different factors influencing lifetime accumulated red bone marrow dose, such as calendar year, age and sex. The lifetime dose was estimated for controls interviewed in person (N = 2811, 37.5% women) of the population-based representative Northern Germany Leukemia and Lymphoma Study. Data were assessed in standardized computer-assisted personal interviews. The calculation of doses is based on a comprehensive quantification model including calendar year, sex, kind of examination, and technical development. In multivariate regression models the annual red bone marrow dose was analyzed depending on age, sex and calendar year to consider simultaneously temporal changes in radiologic practice and individual risk factors. While the number of examinations continuously rises over time, the dose shows two peaks around 1950 and after 1980. Men are exposed to higher doses than woman. Until 1970 traditional examinations like conventional and mass screening examinations caused the main dose. They were then replaced by technically advanced examinations mainly computed tomography and cardiac catheter. The distribution of the red bone marrow dose over lifetime depends highly on the technical standards and radiation protection survey. To a lesser extent it is influenced by age and sex of the subjects. Thus epidemiological studies concerning the assessment of radiation exposure should consider the calendar year in which the examination was conducted.

Reduction of operator radiation dose by a pelvic lead shield during cardiac catheterization by radial access: comparison with femoral access.

OBJECTIVES: This study sought to determine the efficacy of patient pelvic lead shielding for the reduction of operator radiation exposure during cardiac catheterization via the radial access in comparison with the femoral access. BACKGROUND: Cardiac catheterization via the radial access is associated with significantly increased radiation dose to the patient and the operator. Improvements in radiation protection are needed to minimize this drawback. Pelvic lead shielding has the potential to reduce operator radiation dose. METHODS: We randomly assigned 210 patients undergoing elective coronary angiography by the same operator to a radial and femoral access with and without pelvic lead shielding of the patient. Operator radiation dose was measured by a radiation dosimeter attached to the outside breast pocket of the lead apron. RESULTS: For radial access, operator dose decreased from 20.9 ± 13.8 µSv to 9.0 ± 5.4 µSv, p < 0.0001 with pelvic lead shielding. For femoral access, it decreased from 15.3 ± 10.4 µSv to 2.9 ± 2.7 µSv, p < 0.0001. Pelvic lead shielding significantly decreased the dose-area product-normalized operator dose (operator dose divided by the dose-area product) by the same amount for radial and femoral access (0.94 ± 0.28 to 0.39 ± 0.19 µSv × Gy(-1) × cm(-2) and 0.70 ± 0.26 to 0.16 ± 0.13 µSv × Gy(-1) × cm(-2), respectively). CONCLUSIONS: Pelvic lead shielding is highly effective in reducing operator radiation exposure for radial as well as femoral procedures. However, despite its use, radial access remains associated with a higher operator radiation dose.

The deviation of liver dose in real patients for thoracic computed tomography scans: a new approach to individual dosimetry with methods of radiotherapy treatment planning.

The increasing use of computed tomography (CT) in diagnostic imaging is associated with a relevant increase in patient dose and requires CT dose optimization. Anthropomorphic phantoms and mathematical patient models have been developed to improve the dosimetry in diagnostic imaging. Nevertheless, the doses calculated in these models and the ones individual patients can receive may differ considerably. In particular, the assessment of organ doses is problematic when organs and tissues receive only a partial exposure. A typical example for this situation is the exposure of the liver within a thoracic CT. To evaluate the impact of the field boundary and the liver volume on the individual organ dose, 50 CT scans from 25 male and 25 female patients between the ages of 27 to 87 were analyzed in this study with the volumetric tools of a treatment planning system for radiotherapy. The relative volume of the liver within a thoracic CT was assessed and compared to results from dosimetry methods using standardized patient models. The differences between an individual dose and the results from standardized patients are considerable. The fraction of the liver volume within a thoracic CT with a standard lower boundary extends from 48-92%, resulting in a possible dose difference of up to a factor of 1.7. Results from mathematical phantoms can underestimate the liver dose by more than a factor of 2.6. From the determined data, correction factors for the dosimetry of the liver using standard programs can be derived.

An analytic approach to double dosimetry algorithms in occupational dosimetry using energy dependent organ dose conversion coefficients.

Personnel dose in diagnostic radiology is often underestimated. Typically the effective dose E is estimated based on dosimeters worn underneath the protective clothing measuring the personal dose equivalent Hp(10). This one-spot-measurement systematically neglects the exposure to the unshielded organs in the head and neck region. In this paper, energy dependent double dosimetry algorithms in the range of 30-80 keV are derived using organ dose conversion coefficients. The doses of shielded organs are assigned to a single dosimeter in the anterior thoracic region (chest) underneath the apron (Hp,c,u), and the doses of the organs not shielded are assigned to another dosimeter placed on the front area of the neck over the protective garment (Hp,n,o) with E = a1 Hp,c,u(10) + a2 Hp,n,o(10). Organs not completely shielded are categorized correspondingly. The coefficients a1 and a2 increase with higher energies up to 70 keV. The factors a2 are clearly higher according to ICRP 103 (rather than ICRP 60) because ICRP 103 considers additional organs in the head and neck region. According to ICRP 103, a conservative general algorithm with thyroid protection is E = 0.84 Hp,c,u(10) + 0.051 Hp,n,o(10) and without thyroid protection E = 0.79 Hp,c,u(10) + 0.100 Hp,n,o(10).

Cardiac catheterization: impact of face and neck shielding on new estimates of effective dose.

Optimization of radiation protection devices for the operator is achieved by minimizing the effective dose (E) on the basis of the recommendations of Publications 60 and 103 of the International Commission on Radiological Protection (ICRP). Radiation exposure dosimetry was performed with thermoluminescence dosimeters using one Alderson phantom in the patient position and a second one in the typical position of the operator. Various types of protective clothing as well as fixed leaded shieldings (table mounted shielding and overhead suspended shields) were considered calculating E. Shielding factors for protective equipment can readily be misinterpreted referring to the reduction of the effective dose because fixed protective barriers as well as radiation protection clothing are shielding only parts of the body. With the ICRP 103 approach relative to the exposure without lead protection, a lead apron of 0.35 or 0.5 mm thickness reduces E to 14.4 or 12.3%, respectively; by using an additional thyroid collar, these values are reduced to 9.7 or 7.5%. A thyroid collar reduces the effective dose by more than an increase of the lead equivalency of the existing apron. Wearing an apron of 0.5 mm lead-equivalent with a thyroid collar and using an additional side shield, E decreases to 6.8%. Using both a fixed side and face shield decreases E to 2.0%. For protective garments including thyroid protection, the values of the effective dose in cardiac catheterization are 47-106% higher with ICRP 103 than with ICRP 60 recommendations. This is essentially caused by the introduction of new factors for organs in the head and neck region in ICRP 103.

Effective dose estimation in diagnostic radiology with two dosimeters: impact of the 2007 recommendations of the ICRP.

In many standard situations in radiation protection the effective dose is underestimated if it is based on the depth personal dose equivalent Hp(10) measured with a single dosimeter in the anterior thoracic region (chest) underneath the protective apron (Hp,c,u). The estimate can be significantly improved by inclusion of a second dosimeter worn on the front area of the neck over of the protective garment (Hp,n,o) representing organs and areas that are usually not completely covered by the protective garment. The recent recommendations of the International Commission on Radiological Protection (ICRP) emphasize the contribution of the head and neck region to the effective dose. This accentuates the need for a valid representation of this body region in the effective dose algorithm. In this paper we derived coefficients for the two-dosimeter situation using phantom measurements for selected radiological procedures with different geometries between patient and investigator. According to ICRP 60, the algorithm with {without} thyroid protection is E = 0.64{0.64} Hp,c,u + 0.016{0.073} Hp,n,o. According to ICRP 103, the algorithm becomes E = 0.60{0.60} Hp,c,u + 0.047{0.094} Hp,n,o. The ICRP 103 model reveals that the underestimation of the effective dose based on Hp(10) using a single dosimeter worn under the protective garment is even higher than previously assumed based on ICRP 60. Future personal dosimetry should be qualified by a two-dosimeter concept. The head and neck region which is not covered by a conventional protective garment needs to be protected by mounted shielding or other constructive measures.

Randomized comparison of operator radiation exposure during coronary angiography and intervention by radial or femoral approach.

Controversial data have been published on the amount of radiation exposure during radial coronary procedures. We hypothesized that in the current era, high-volume operators with optimal technique would not be exposed to higher radiation doses during radial procedures. A total of 297 patients undergoing cardiac catheterization (195 elective diagnostic coronary angiograms and 102 elective coronary interventions) were prospectively assigned in a random fashion to the radial access (RA) or femoral access (FA). All procedures were performed by the same operator with vast experience in radial procedures and standard measures for radiation protection were used. Operator radiation exposure was measured with an electronic radiation dosimeter attached to the breast pocket of the operator on the outside of the lead apron and estimates of the ambient dose equivalent were derived. For coronary angiograms, fluoroscopy time (2.8 +/- 2.1 vs. 1.7 +/- 1.4 min; P < 0.001) and dose-area product (15.1 +/- 8.4 vs. 13.1 +/- 8.5 Gy x cm(2); P < 0.05) were increased by 18% and 15%, respectively, for RA vs. FA. Operator radiation exposure was 100% higher for the RA compared to the FA (64 +/- 55 vs. 32 +/- 39 microSv; P < 0.001). For coronary interventions, fluoroscopy time (11.4 +/- 8.4 vs. 10.4 +/- 6.8 min; P = NS) and dose-area product (46.3 +/- 28.7 vs. 51.0 +/- 29.4 Gy x cm(2); P = NS) for RA and FA were not statistically different. However, operator radiation exposure was increased by 51% for the RA compared to the FA (166 +/- 188 vs. 110 +/- 115 microSv; P < 0.05). This study demonstrates that the radial approach is burdened with a 100% increase in operator radiation exposure during diagnostic coronary catheterization procedures and a 50% increase during coronary interventions, provided that no special devices for radiation protection are used. Measurements of radiation dose, such as fluoroscopy time and dose-area product, substantially underestimate the disproportionate rise in radiation exposure. Special precautions are warranted to improve radiation protection during invasive coronary procedures via the radial approach.