Measured scattered x-ray energy spectra for simulated irradiation geometries in diagnostic radiology

Energy spectrum measurement of scattered X-rays during IVR procedure

With the increase of the number of interventional radiology (IVR) procedures, the occupational exposure of operators and medical staff has attracted keen attention. The energy of scattered radiation in medical clinical sites is important for estimating the biological effects of occupational exposure. Recent years have seen many reports on the dose of scattered radiation by IVR, but few on the energy spectrum. In this study, the energy spectrum of scattered X-rays was measured by using a cadmium telluride (CdTe) semiconductor detector during IVR on several neurosurgical and cardiovascular cases. The cumulated spectra in each case were compared. The spectra showed little changes among neurosurgical cases and relatively large changes among cardiovascular cases. This was assumed to be due to the change of X-ray tube voltage and tube angle was larger in cardiovascular cases. The resulting energy spectra will be essential for the assessment of detailed biological effects of occupational exposure.

Performance of elastic x-ray shield made by embedding Bi2 O3 particles in porous polyurethane

BACKGROUND

Many healthcare institutions have guidelines concerning the usage of protective procedures, and various x-ray shields have been used to reduce unwanted radiation exposure to medical staff and patients when using x-rays. Most x-ray shields are in the form of sheets and lack elasticity, which limits their effectiveness in shielding areas with movement, such as the thyroid. To overcome this limitation, we have developed an innovative elastic x-ray shield.

PURPOSE

The purpose of this study is to explain the methodology for developing and evaluating a novel elastic x-ray shield with sufficient x-ray shielding ability. Furthermore, valuable knowledge and evaluation indices are derived to assess our shield's performance.

METHODS

Our x-ray shield was developed through a process of embedding Bi2 O3 particles into porous polyurethane. Porous polyurethane with a thickness of 10 mm was dipped into a solution of water, metal particles, and chemical agents. Then, it was air-dried to fix the metal particles in the porous polyurethane. Thirteen investigational x-ray shields were fabricated, in which Bi2 O3 particles at various mass thicknesses (ranging from 585 to 2493 g/m2 ) were embedded. To determine the performance of the shielding material, three criteria were evaluated: (1) Dose Reduction Factor (D R F $DRF$ ), measured using inverse broad beam geometry; (2) uniformity, evaluated from the standard deviation (S D $SD$ ) of the x-ray image obtained using a clinical x-ray imaging detector; and (3) elasticity, evaluated by a compression test.

RESULTS

The elastic shield with small pores, containing 1200 g/m2 of the metal element (Bi), exhibited a well-balanced performance. TheD R F $DRF$ was approximately 80% for 70 kV diagnostic x-rays. This shield's elasticity was -0.62 N/mm, a loss of only 30% when compared to porous polyurethane without metal. Although the non-uniformity of the x-ray shield leads to poor shielding ability, it was found that the decrease in the shielding ability can be limited to a maximum of 6% when the shield is manufactured so that theS D $SD$ of the x-ray image of the shield is less than 10%.

CONCLUSIONS

It was verified that an elastic x-ray shield that offers an appropriate reduction in radiation exposure can be produced by embedding Bi2 O3 particles into porous polyurethane. Our findings can lead to the development of novel x-ray shielding products that can reduce the physical and mental stress on users.

Technical note: Characteristics of the energy spread kernels of scattered radiation in an x-ray room

PURPOSE

To describe the scattered radiation spectra inside an x-ray room for different scattering conditions.

METHODS

Monte Carlo simulations of an x-ray room using phantoms of different size, varying field sizes, and a range of mono-energetic beams were carried out. For each energy, the particle fluence spectrum of scattered photons was collected at different spherical zones to describe the radiation reaching the different boundaries of the x-ray room. The effect on the scattered spectrum of the room floor was also considered.

RESULTS

The scattered spectra for mono-energetic primary beams at a given spherical zone give rise to oriented energy spread kernels (OESKs) that can be used to calculate the scattered spectrum for any poly-energetic beam at that zone. Despite the large differences, which can be seen in the OESKs when the scattering conditions vary, an important invariance is also observed: the position of the broad scatter peak for a given primary energy and zone.

CONCLUSIONS

The result of breaking down the calculation of the scattered radiation spectrum into the different factors that influence it allows estimating the spectrum in a wide range of situations. The invariant position of the broad scatter peak can be used to estimate the highest energy of the scattered photons for a given primary energy and zone, which may determine radiation shielding needs.

Reducing stray radiation with a novel detachable lead arm support in percutaneous coronary intervention

BACKGROUND

Placing radioprotective devices near patients reduces stray radiation during percutaneous coronary intervention (PCI), a promising technique for treating coronary artery disease. Therefore, lead arm support may effectively reduce occupational radiation dose to cardiologists.

PURPOSE

We aimed to estimate the reduction of stray radiation using a novel detachable lead arm support (DLAS) in PCI.

MATERIALS AND METHODS

A dedicated cardiovascular angiography system was equipped with the conventional 0.5-mm lead curtain suspended from the table side rail. The DLAS was developed using an L-shaped acrylic board and detachable water-resistant covers encasing the 0.5-, 0.75-, or 1.0-mm lead. The DLAS was placed adjacent to a female anthropomorphic phantom lying on the examination tabletop at the patient entrance reference point. An ionization chamber survey meter was placed 100 cm away from the isocenter to emulate the cardiologist's position. Dose reduction using the L-shaped acrylic board, DLAS, lead curtain, and their combination each was measured at five heights (80-160 cm in 20-cm increments) when acquiring cardiac images of the patient phantom with 10 gantry angulations, typical for PCI.

RESULTS

Median dose reductions of stray radiation using the L-shaped acrylic board were 9.0%, 8.8%, 12.4%, 12.3%, and 6.4% at 80-, 100-, 120-, 140-, and 160-cm heights, respectively. Dose reduction using DLAS with a 0.5-mm lead was almost identical to that using DLAS with 0.75- and 1.0-mm leads; mean dose reductions using these three DLASs increased to 16.2%, 45.1%, 66.0%, 64.2%, and 43.0%, respectively. Similarly, dose reductions using the conventional lead curtain were 95.9%, 95.5%, 83.7%, 26.0%, and 19.6%, respectively. The combination of DLAS with 0.5-mm lead and lead curtain could increase dose reductions to 96.0%, 95.8%, 93.8%, 71.1%, and 47.1%, respectively.

CONCLUSIONS

DLAS reduces stray radiation at 120-, 140-, and 160-cm heights, where the conventional lead curtain provides insufficient protection.

High filtration in interventional practices reduces patient radiation doses but not always scatter radiation doses

OBJECTIVES

In fluoroscopy-guided interventional practices, new dose reduction systems have proved to be efficient in the reduction of patient doses. However, it is not clear whether this reduction in patient dose is proportionally transferred to operators' doses. This work investigates the secondary radiation fields produced by two kinds of interventional cardiology units from the same manufacturer with and without dose reduction systems.Methods:Data collected from a large sample of clinical procedures over a 2-year period (more than 5000 procedures and 340,000 radiation events) and the DICOM radiation dose structured reports were analysed.

RESULTS

The average cumulative H_p(10) per procedure measured at the C-arm was similar for the standard and the dose reduction systems (452 vs 476 μSv respectively). The events analysis showed that the ratio H_p(10)/KAP at the C-arm was (mean ± SD) 5 ± 2, 10 ± 4, 14 ± 4 and 14 ± 6 μSv·Gy^-1·cm^-2 for the beams with no added filtration, 0.1, 0.4 and 0.9 mm Cu respectively and suggested that the main cause for the increment of the ratio H_p(10)/KAP vs the "standard system" is the use of higher beam filtration in the "dose reduction" system.

CONCLUSION

Dose reduction systems are beneficial to reduce KAP in patients and their use should be encouraged, but they may not be equally effective to reduce occupational doses. Interventionalists should not overlook their own personal protection when using new technologies with dose reduction systems.

ADVANCES IN KNOWLEDGE

Dose reduction technology in interventional systems may increase scatter dose for operators. Personal protection should not be overlooked with dose reduction systems.

Characterisation and mapping of scattered radiation fields in interventional radiology theatres

We used the Timepix3 hybrid pixel detector technology in order to determine the exposure of medical personnel to ionizing radiation in an interventional radiology room. We measured the energy spectra of the scattered radiation generated by the patient during X-ray image-guided interventional procedures. We performed measurements at different positions and heights within the theatre. We first observed a difference in fluence for each staff member. As expected, we found that the person closest to the X-ray tube is the most exposed while the least exposed staff member is positioned at the patient’s feet. Additionally, we observed a shift in energy from head to toe for practitioners, clearly indicating a non-homogenous energy exposure. The photon counting Timepix3 detector provides a new tool for radiation field characterisation that is easier-to-use and more compact than conventional X-ray spectrometers. The spectral information is particularly valuable for optimising the use of radiation protection gear and improving dosimetry surveillance programs. We also found the device very useful for training purposes to provide awareness and understanding about radiation protection principles among interventional radiology staff.

Evaluation of stray radiation to the operator for five hand-held dental X-ray devices

OBJECTIVES

Evaluate stray radiation to the operator, as represented by a plane within the significant zone of occupancy (SZO), produced by five models of hand-held intraoral dental X-ray devices (HIDXDs).

METHODS

The stray radiation for five models of HIDXDs was measured, using an anthropomorphic tissue-equivalent head phantom as a scattering object. An ionization chamber was used to measure the air kerma (μGy) at 63 positions in a 160 cm high by 60 cm wide plane that was 10 cm behind the X-ray device, identified as being within the SZO.

RESULTS

Based on the measured air kerma from stray radiation of five different HIDXDs, the estimated annual air kerma at all measured spatial positions was calculated. When calculated using a median air kerma of 0.8 mGy at the distal end of the cone, as typically required for digital image receptors, 1 the ranges for estimated annual air kerma in the SZO across the devices were 0.14-0.77 mGy for the median, 0.41-1.01 mGy for the mean, and 1.32-2.55 mGy for the maximum. Similarly, when calculated using a median air kerma of 1.6 mGy as typically required for D-speed film, 2 the ranges for estimated annual air kerma across the devices were 0.28-1.54 mGy for the median, 0.83-2.03 mGy for the mean, and 2.64-5.10 mGy for the maximum.

CONCLUSIONS

From measured air kerma values of stray radiation in the SZO, estimated annual exposures to the operator for HIDXDs are expected to be greater than from conventional wall-mounted or portable devices activated from a protected area (at a distance or behind shielding). HIDXDs should therefore only be used when patient accessibility makes their use necessary and the use of a portable device on a stand or a wall-mounted device is not reasonably feasible. This approach would keep occupational radiation exposures of dental workers as low as reasonably achievable.

Estimating head and neck tissue dose from x-ray scatter to physicians performing x-ray guided cardiovascular procedures: a phantom study

Physicians performing x-ray guided interventional procedures have a keen interest in radiation safety. Radiation dose to tissues and organs of the head and neck are of particular interest because they are not routinely protected by wearable radiation safety devices. This study was conducted to facilitate estimation of radiation dose to tissues of the head and neck of interventional physicians based on the dose recorded by a personal dosimeter worn on the left collar. Scatter beam qualities maximum energy and HVL were measured for 40 scatter beams emitting from an anthropomorphic patient phantom. Variables of the scatter beams included scatter angle (35° and 90°), primary beam peak tube potential (60, 80, 100, and 120 kVp), and 5 Cu spectral filter thicknesses (0-0.9 mm). Four reference scatter beam qualities were selected to represent the range of scatter beams realized in a typical practice. A general radiographic x-ray tube was tuned to produce scatter-equivalent radiographic beams and used to simultaneously expose the head and neck of an anthropomorphic operator phantom and radiochromic film. The geometric relationship between the x-ray source of the scatter-equivalent beams and the operator phantom was set to mimic that between a patient and physician performing an invasive cardiovascular procedure. Dose to the exterior surface of the operator phantom was measured with both 3 × 3 cm² pieces of film and personal dosimeters positioned at the location of the left collar. All films were scanned with a calibrated flatbed scanner, which converted the film's reflective density to dose. Films from the transverse planes of the operator phantom provided 2D maps of the dose distribution within the phantom. These dose maps were normalized by the dose at the left collar, providing 2D percent of left collar dose (LCD) maps. The percent LCD maps were overlain with bony anatomy CT images of the operator phantom and estimates of percent LCD to the left, right and whole brain, brain stem, lenses of the eyes, and carotid arteries were calculated. Per expectation, results indicated greater percent dose to superficial versus deep tissues and increasing percent dose to deep tissues with increasing scatter-equivalent beam energy and HVL. The results enable estimation of the scatter dose to tissues of the head and neck of interventional physicians based on occupational dose measured by a personal dosimeter worn at the collar outside the protective apron.

Monte Carlo Modeling of Computed Tomography Ceiling Scatter for Shielding Calculations

Radiation protection for clinical staff and members of the public is of paramount importance, particularly in occupied areas adjacent to computed tomography scanner suites. Increased patient workloads and the adoption of multi-slice scanning systems may make unshielded secondary scatter from ceiling surfaces a significant contributor to dose. The present paper expands upon an existing analytical model for calculating ceiling scatter accounting for variable room geometries and provides calibration data for a range of clinical beam qualities. The practical effect of gantry, false ceiling, and wall attenuation in limiting ceiling scatter is also explored and incorporated into the model. Monte Carlo simulations were used to calibrate the model for scatter from both concrete and lead surfaces. Gantry attenuation experimental data showed an effective blocking of scatter directed toward the ceiling at angles up to 20-30° from the vertical for the scanners examined. The contribution of ceiling scatter from computed tomography operation to the effective dose of individuals in areas surrounding the scanner suite could be significant and therefore should be considered in shielding design according to the proposed analytical model.

Organ-specific external dose coefficients and protective apron transmission factors for historical dose reconstruction for medical personnel

While radiation absorbed dose (Gy) to the skin or other organs is sometimes estimated for patients from diagnostic radiologic examinations or therapeutic procedures, rarely is occupationally-received radiation absorbed dose to individual organs/tissues estimated for medical personnel; e.g., radiologic technologists or radiologists. Generally, for medical personnel, equivalent or effective radiation doses are estimated for compliance purposes. In the very few cases when organ doses to medical personnel are reconstructed, the data is usually for the purpose of epidemiologic studies; e.g., a study of historical doses and risks to a cohort of about 110,000 radiologic technologists presently underway at the U.S. National Cancer Institute. While ICRP and ICRU have published organ-specific external dose conversion coefficients (DCCs) (i.e., absorbed dose to organs and tissues per unit air kerma and dose equivalent per unit air kerma), those factors have been published primarily for mono-energetic photons at selected energies. This presents two related problems for historical dose reconstruction, both of which are addressed here. It is necessary to derive conversion factor values for (1) continuous distributions of energy typical of diagnostic medical x-rays (bremsstrahlung radiation), and (2) energies of particular radioisotopes used in medical procedures, neither of which are presented in published tables. For derivation of DCCs for bremsstrahlung radiation, combinations of x-ray tube potentials and filtrations were derived for different time periods based on a review of relevant literature. Three peak tube potentials (70 kV, 80 kV, and 90 kV) with four different amounts of beam filtration were determined to be applicable for historic dose reconstruction. The probabilities of these machine settings were assigned to each of the four time periods (earlier than 1949, 1949-1954, 1955-1968, and after 1968). Continuous functions were fit to each set of discrete values of the ICRP/ICRU mono-energetic DCCs and the functions integrated over the air-kerma weighted photon fluence of the 12 defined x-ray spectra. The air kerma-weighted DCCs in this work were developed specifically for an irradiation geometry of anterior to posterior (AP) and for the following tissues: thyroid, breast, ovary, lens of eye, lung, colon, testes, heart, skin (anterior side only), red bone marrow (RBM), and brain. In addition, a series of functional relationships to predict DT Ka-1 values for RBM dependent on body mass index [BMI (kg m-2) ≡ weight per height] and average photon energy were derived from a published analysis. Factors to account for attenuation of radiation by protective lead aprons were also developed. Because lead protective aprons often worn by radiology personnel not only reduce the intensity of x-ray exposure but also appreciably harden the transmitted fluence of bremsstrahlung x-rays, DCCs were separately calculated for organs possibly protected by lead aprons by considering three cases: no apron, 0.25 mm Pb apron, and 0.5 mm Pb apron. For estimation of organ doses from conducting procedures with radioisotopes, continuous functions of the reported mono-energetic values were developed, and DCCs were derived by estimation of the function at relevant energies. By considering the temporal changes in primary exposure-related parameters (e.g., energy distribution), the derived DCCs and transmission factors presented here allow for more realistic historical dose reconstructions for medical personnel when monitoring badge readings are the primary data on which estimation of an individual's organ doses are based.

Investigation of scatter fractions for estimating leakage dose in medical X-ray imaging facilities

It is essential to make accurate estimates of the scatter of radiation from the human body when calculating the leakage dose in medical X-ray imaging facilities. The scatter fraction varies with the size and shape of the radiation field in a way that is not exactly proportional to the area of the field. Japanese law quotes values for the scatter fraction that are provided by the National Council on Radiation Protection and Measurements, but these data were obtained 30 years ago, using equipment that differed considerably from that employed nowadays. To date, no attempt has been made to confirm whether these data accurately describe current Japanese equipment. In the present study, we used an ion chamber dosimeter to measure scattered radiation fractions, and new scatter factor data are presented that resolve these problems.

An investigation of operator exposure in interventional radiology

A study was conducted to investigate how operator exposure in interventional radiology is affected by various common fluoroscopic imaging conditions. Stray radiation levels surrounding the imaging chain of a C-arm angiographic system were measured with an anthropomorphic abdomen phantom under different imaging conditions, and isodose curves were constructed. Operator exposure was shown to increase with patient dose-area product as the imaging field of view (FOV) is changed, with the highest scatter levels occurring with an intermediate-sized FOV. Use of copper spectral beam filtration was found to result in decreased operator exposure, whereas use of wedge-shaped equalization filters was found to increase exposure. The effect of increasing patient abdomen thickness was simulated by surrounding the phantom with plastic bolus material. Increasing the thickness by 5 cm resulted in a doubling of exposure at the operator's waist. Exposure to the operator's upper body was significantly reduced when the FOV was positioned on the far side of the patient. Operator exposure can be maintained at an acceptable level by taking these variables into consideration and incorporating the suggested dose reduction techniques into routine practice to the greatest extent possible.

Measurement of backscattered x-ray spectra at the water surface in the energy range 60 kV to 120 kV

Backscattered x-ray spectra at the water surface have been measured by using a small silicon diode detector. The measurements have been made at tube voltages 60 kV to 120 kV (HVL 2.4-6.1 mm Al) and field sizes 5 x 5 cm2 to 30 x 30 cm2. The measured spectra are corrected for detector distortion and for the angular dependence of detector efficiency. The obtained backscattered spectrum has a lower mean energy and a narrower shape than the primary spectrum. The ratio of the mean energy of the backscattered spectrum to that of the primary spectrum is between 0.83 and 0.94. The ratio of the spectrum width at 10% of the continuous spectrum maximum is between 0.65 and 0.78. The change of spectral shape due to the field size is slight. In the high-voltage spectra, the peak due to the Compton scattering of tungsten Kalpha x-rays is observed. The backscatter factors (BSFs) calculated from the obtained spectra show a satisfactory agreement with other studies. The difference between the BSF defined as the ratio of air kerma and the BSF defined as the ratio of water kerma is also calculated; the maximum difference is 0.43%. The empirical equation showing the relation between the two BSFs is presented.

Evaluation of protective shielding thickness for diagnostic radiology rooms: theory and computer simulation

This work presents the development and evaluation using modern techniques to calculate radiation protection barriers in clinical radiographic facilities. Our methodology uses realistic primary and scattered spectra. The primary spectra were computer simulated using a waveform generalization and a semiempirical model (the Tucker-Barnes-Chakraborty model). The scattered spectra were obtained from published data. An analytical function was used to produce attenuation curves from polychromatic radiation for specified kVp, waveform, and filtration. The results of this analytical function are given in ambient dose equivalent units. The attenuation curves were obtained by application of Archer's model to computer simulation data. The parameters for the best fit to the model using primary and secondary radiation data from different radiographic procedures were determined. They resulted in an optimized model for shielding calculation for any radiographic room. The shielding costs were about 50% lower than those calculated using the traditional method based on Report No. 49 of the National Council on Radiation Protection and Measurements.

A comparison of mammography spectral measurements with spectra produced using several different mathematical models

Due to the relatively complex nature of spectral measurements from x-ray machines, many researchers use mathematical models to simulate the spectra they need. However, there is concern over their accuracy, and hence the impact that their accuracy may have, on subsequent calculations that rely upon the spectra modelled. With this in mind spectral measurements have been performed on a mammography machine and a comparison with spectra calculated using several different models is presented. Several different techniques have been investigated in the spectral measurements to allow for pulse pileup and other effects of high count rate. Comparison with half value layer (HVL) measurements shows that the use of a gating signal in conjunction with the air-free path provides accurate results without the need for a pinhole collimator. Comparison of the measured spectra with those calculated using different models proposed in the literature suggests that accurate results can be produced by all models, but only if the user attempts to match the calculated HVL of the modelled spectrum with the physically measured HVL. If this is not done the modelled spectra may be in error. The impact of such an error is demonstrated in calculations of mean glandular dose, which indicate a possible underestimate of the dose by up to 20%.