[The First Step in the Optimization of Radiation Protection of Patients in Cerebral Angiography: Investigate the Possibility of Constructing the Diagnostic Reference Level by Imaging Objective/Disease Group Using Display Value of the Blood Vessel Imaging Apparatus].

To optimize the radiation protection of patients, we investigated the possibility of constructing the diagnostic reference levels (DRLs) by imaging objective/disease group using display value of the blood vessel imaging apparatus (air kerma-area product: PKA, air kerma at the patient entrance reference point: Ka, r) in cerebral angiography. We used PKA and Ka, r recorded during surgery of 997 patients at our hospital, and classified them according to the purpose of imaging (diagnostic cerebral angiography or neuro interventional radiology) and disease group. Neuro interventional radiology (PKA: 268±155 Gy・cm2, Ka, r: 2420±1462 mGy) was significantly higher than that of diagnostic cerebral angiography (PKA: 161±70 Gy・cm2, Ka, r: 1112±485 mGy), (Mann-Whitney test, P<0.01). Significant difference was found between PKA and Ka, r for imaging purpose and disease group (Kruskal-Wallis test, P<0.05). It is highly probable that the DRL for cerebral angiography can be constructed by imaging purpose/disease group using display value (PKA, Ka, r) of the blood vessel imaging apparatus.

[Construction of System for Support of Multifacility IVR Dose Analysis and Research].

Although measurement and management of angiographic entrance skin dose (ESD) are deemed extremely important, accurate determination of maximum ESD and its location is generally difficult because of the dependence on therapeutic technique and position. Following our development of body-mounted gear bearing radiophotoluminescence glass dosimeter (RPLD) arrays for direct measurement of ESD in cranial and cardiovascular angiography and interventional radiology (IVR), our focus next turned to the limited number of facilities equipped to read RPLD outputs and the need for methods to effectively provide feedback to clinical facilities. As described here, we first constructed an RPLD reading facility capable of sending and receiving RPLDs by post, offering the potential to enable utilization of the developed gear at all hospitals in Japan that perform angiography and IVR. We next developed specialized web-based system to generate dose maps from RPLD dose data, thereby enabling any facility to perform trial system analysis, evaluation, and implementation; and investigated the results and related problems.

[The Need for Lens Radiation Protection for Healthcare Provider in Open and Internal Fixation of the Hip Joint].

Increased occupational exposure of radiation workers is a major problem during open reduction and internal fixation (ORIF) of the hip joint, as the surgeon's eye lens is in close proximity to the patient and the X-ray tube. The purposes of this study were to clarify the occupational exposure of radiation workers during ORIF of the hip joint and to examine the need for radiation protection measures. The radiation exposure of radiation workers was evaluated by making an airborne dose distribution map using phantom experiments. The radiation goggles attached with a small optically stimulated luminescence dosimeter were used in clinical practice to measure the lens dose received by the surgeon, and the necessity of radiation goggles was examined. The airborne dose distribution in ORIF of the hip joint showed a wider area of high dose rate during axial fluoroscopy of the femoral neck than during posterior-anterior fluoroscopy. In axial fluoroscopy of the femoral neck, the surgeon was always in the high dose rate range of 10 µGy/min or higher, the nurses were in the dose rate range of 4 to 10 µGy/min, and the radiologic technologists were in the dose rate range of 0.5 µGy/min or lower. The maximum 3 mm dose equivalent to the surgeon per case was 0.38 mSv. In contradiction, radiation goggles were useful in ORIF because they provided approximately 60% shielding. It is advisable to work with radiation goggles to avoid cataracts.

Background Factors Affecting the Radiation Exposure of the Lens of the Eye among Nurses in Interventional Radiology: A Quantitative Observational Study.

With the International Commission on Radiological Protection's (ICRP) reduction in the radiation dose threshold for cataracts, evaluating and preventing radiation exposure to the lens of the eye among interventional radiology (IR) staff have become urgent tasks. In this study, we focused on differences in lens-equivalent dose (HT Lens) to which IR nurses in three hospitals were exposed and aimed to identify factors underlying these differences. According to analyses of time-, distance-, and shielding-related factors, the magnitude of the HT Lens dose to which IR nurses were exposed could be explained not by time or shielding but by the distance between the X-ray exposure field and the location of the IR nurse. This distance tended to be shorter in hospitals with fewer staff. The most effective means of reducing the exposure of the lenses of IR nurses' eyes to radiation is to position them at least two meters from the radiation source during angiography procedures. However, some hospitals must provide IR departments with comparatively few staff. In work environments where it is infeasible to reduce exposure by increasing distance, interventions to reduce time by managing working practices and investment in shielding equipment are also important. This study was not registered.

The Effect of Pre-Operative Verbal Confirmation for Interventional Radiology Physicians on Their Use of Personal Dosimeters and Personal Protective Equipment.

Interventional radiology (IR) physicians must be equipped with personal passive dosimeters and personal protective equipment (PPE); however, they are inconsistently used. Therefore, we aimed to explore practical measures to increase PPE usage and ascertain whether these measures could lead to an actual decrease in exposure doses to IR physicians. Dosimeters and PPE were visually inspected. Then, a pre-operative briefing was conducted as a direct intervention, and the use of dosimeters and PPE was verbally confirmed. Finally, the intervention effect was verified by measuring the use rates and individual exposure doses. Because of the intervention, the use rate markedly improved and was almost 100%. However, both the effective dose rate (effective dose/fluoroscopy time) and the lens equivalent dose rate (lens equivalent dose/fluoroscopy time) showed that the intervention led to a statistically significant increase in exposure (effective dose rate: p = 0.033; lens equivalent dose rate: p = 0.003). In conclusion, the proper use of dosimeters and PPE raised the radiation exposure values for IR physicians immediately after the intervention, which was hypothesized to be due to the inclusion of exposure overlooked to date and the changes in the dosimeter management method from a single- to a double-dosimeter approach.

[Study of the additional filter in transcatheter hepatic arterial embolization].

It is well known that Interventional Radiology (IVR) is useful. However, the patient dose in IVR is increasing because of the prolongation of fluoroscopic time and the increase in the number of radiographies in recent years. We studied the adequacy of the additional filter for the decrease of the skin surface dose in patients with hepatocellular carcinoma of transcatheter arterial embolization (TAE). In 20 patients (15 men and 5 women, average age: 66.9 and 72.0 years old) who had undergone TAE, we estimated the skin surface dose from the records of their exposure condition (tube voltage, tube current, time, and field size of image intensifier) and the results of the phantom experiment with 2 kinds of additional filter. The estimated skin surface dose of the patient was 1.75 ± 0.84 with the additional filter of 1.5 mm thickness of aluminum (1.5 mmAl), 1.46 ± 0.67 Gy with 0.03 mm thickness tantalum (0.03 mmTa) and 1.17 ± 0.55 Gy with 0.06 mm thickness of tantalum (0.06 mmTa). Against a skin surface dose of 1.5 mmAl, the dose reduction of 16.7% was shown in 0.03 mmTa and 33.2% in 0.06 mmTa. With a DSA phantom of iodine density 0.5 and 1.0 and 2.0 mgI/ml, DSA images were acquisitioned at tube voltage 70, 80 and 90 kV to compare the detectability of contrast media in 0.06 mmTa with 1.5 mmAl. To evaluate the detectability of contrast media in 0.06 mmTa in 1.5 mmAl, receiver operating characteristic (ROC) analysis was performed with the pixel value of the phantom image. The area under the ROC curve in a 1.5 mmAl filter and the 0.06 mmTa filter provided with each contrast media density and each tube voltage was approximately a constant value. It was suggested that there was no differences in the detectability of contrast media in both additional filters. In conclusion, the skin surface dose of the patient was able to be reduced 33.2% without decreasing contrast media detectability by changing the additional filter from 1.5 mmAl to 0.06 mmTa. It was most suitable in TAE in our hospital to choose 0.06 mmTa as an additional filter.

[Method of calculating patient skin surface dose in transcatheter arterial embolization].

The usefulness of interventional radiology (IVR) in clinical practice is well known. However, patient dose in IVR has recently been increased as a result of the prolongation of fluoroscopic time and the increased number of radiographies. We studied a simple method of calculating skin surface dose in patients who underwent transcatheter arterial embolization (TAE) for the treatment of hepatocellular carcinoma by obtaining the value of a dose area product meter attached to the digital subtraction angiography system. In 20 subjects (15 men and 5 women, aged an average of 68.2+/-7.3 years, respectively) who underwent TAE, exposure conditions (tube voltage, tube current, time, and size of image intensifier) in a time series and last value indicated on the dose area product meter were recorded. A dosimetric phantom was placed at a position the same as that of the patient for TAE, the surface dose (SD) of the phantom was measured under various exposure conditions, and SD per unit mAs (SD/mAs) was obtained. Then the skin surface dose in each subject was estimated from the values of the exposure condition and SD/mAs. A high correlation was observed between the last value (x) on the dose area product meter and the estimated skin surface dose (y) (r=0.933), and the following regression equation was derived: y=0.005x-0.589. The skin surface dose calculated using the regression equation was compared with that obtained by the method recommended by the Japan Association on Radiological Protection in Medicine (JARPM), considering the value estimated from the value of exposure conditions with SD/mAs as the gold standard. The results indicated that the error in the method using the regression equation was significantly lower than that of the JARPM method (18.3+/-14.0% and 75.5+/-66.0%, respectively, p<0.01). In conclusion, the skin surface dose in TAE could be monitored with high precision using the value of the dose area product meter by obtaining the regression formula between the value of the dose area product meter and the skin surface dose estimated with the phantom values.