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Original Research |
1 Department of Radiology, Teikyo University School of Medicine, 2-11-1, Kaga,
Itabashi-ku, Tokyo 173-8605, Japan. Address correspondence to S. Suzuki.
2 Nagase Landauer, Ltd., Tokyo, Japan.
Received October 10, 2004;
accepted after revision November 15, 2004.
Address correspondence to S. Suzuki.
Abstract
 Top Abstract IntroductionSubjects and MethodsResultsDiscussionAPPENDIX 1: Absorbed Doses...References |
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SUBJECTS AND METHODS. Doses were assessed for 24 procedures: 12 using a new unit with a digital flat-panel system and 12 using a conventional unit. Doses to patients' skin were evaluated with thermoluminescent dosimeters behind the left, middle, and right portions of the liver. The doses to the radiologists were measured by an electronic personal dosimeter placed on the chest outside a lead protector. The maximal skin doses to the patients and the dose equivalents, Hp(0.07), to the radiologists were compared between the two procedure groups with each angiographic unit.
RESULTS. For procedures with the new unit, the mean maximal skin dose to the patients was 284 ± 127 (SD) mGy (range, 130–467 mGy), and Hp(0.07) to the radiologists was 62.8 ± 17.4 µSv. For procedures with the conventional unit, the maximal skin dose to the patients was 1,068 ± 439 mGy (range, 510–1,882 mGy), and Hp(0.07) to the radiologists was 68.4 ± 25.7 µSv. The maximal skin dose to the patients was significantly lower with the new unit than with the conventional unit (p < 0.0005). There was no significant difference in the Hp(0.07) to the radiologists between the two procedure groups.
CONCLUSION. The new digital flat-panel system for angiographic imaging can reduce the radiation dose to patients' skin during TAE for HCC as compared with the conventional system.
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionAPPENDIX 1: Absorbed Doses...References |
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The usefulness of flat-panel radiography has been evaluated in the literature [2–6]. On the other hand, a digital flat-panel system for angiographic imaging became available recently. It has evolved as a new system to deliver high-resolution imaging with high dose efficiency. However, the few reports available on the effect of dose reduction by this system are limited to coronary angiography [7, 8].
In this study, we evaluated the radiation dose to patients' skin and outside the lead protector of radiologists during transcatheter arterial embolization (TAE) for hepatocellular carcinoma (HCC), one of the main abdominal interventional procedures in Japan, and compared a new angiographic unit with a digital flat-panel system and a conventional angiographic unit.
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionAPPENDIX 1: Absorbed Doses...References |
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The Advantx LCA unit has an undercouch tube and an overcouch image intensifier with four fields of view: 16 inches (41 cm), 12 inches (30 cm), 9 inches (23 cm), and 6 inches (15 cm). The 12-inch (30-cm) field of view was used mainly in this assessment. With Advantx LCA, the exposition data for fluoroscopy were 70–80 kV and 1.6–8.4 mA and for digital subtraction angiography were 80 kV and 3.4–35.6 mAs; the high beam filter used consisted of 1-mm aluminum and 0.1-mm copper.
The Innova 4100 unit has an undercouch tube and an overcouch digital flat-panel detector with four fields of view: 40, 32, 20, and 16 cm. A 32-cm field of view was used mainly in this assessment. With Innova 4100 unit, the exposition data for fluoroscopy were 79–85 kV and 1.0–4.2 mA and for digital subtraction angiography were 83–90 kV and 1.1–9.3 mAs; the high beam filter used was 0.1-, 0.2-, or 0.3-mm aluminum and was automatically selected by the system. Innova 4100 performed under automatic exposure control and used two fluoroscopy modes, low and normal, and two digital subtraction angiography modes, low and normal. We used the low modes. At the installation of Innova 4100, several radiologists checked that the quality of the images using the low modes was not worse than that of images obtained with Advantx LCA.
A total of 24 TAE procedures were performed from April to July 2004 (Table 1). Twelve patients (three women and nine men) underwent the procedures on the Advantx LCA unit. The mean patient age was 69.0 ± 9.8 (SD) years (range, 54.1–90.3 years). Twelve other patients (two women and 10 men) underwent the procedures with the Innova 4100 unit. The mean patient age was 73.8 ± 5.4 (SD) years (range, 63.5–80.0 years). The patients were recruited to undergo the procedure on one or the other system according to availability. All patients gave informed consent.
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The procedures were performed by six experienced radiologists using standard techniques. A sheath was placed through the femoral route. Then superior mesenteric arteriography and celiac arteriography were performed using a visceral catheter. The hepatic artery branches supplying HCC were catheterized selectively using a microcatheter and embolized with a mixture of iodized oil and chemotherapeutic agents (mitomycin C and epirubicin hydrochloride), followed by gelatin particles (Gelfoam, UpJohn). This embolization was performed under fluoroscopic observation and was followed by angiography to evaluate the effect of the embolization. The pulse mode was used for fluoroscopy in both angiographic units. The X-ray field was decreased to as small as possible. The power injector was used for infusion of a contrast medium during digital subtraction angiography, unless manual injection was inevitable.
We estimated the effective photon energy of several main modes of fluoroscopy and digital subtraction angiography in TAE with each device by means of optically stimulated luminescence (OSL) dosimeters (Luxel badge, Nagase Landauer). The effective photon energy was 36–42 keV with Advantx LCA and 32–43 keV with Innova 4100.
The absorbed doses in the patients' skin were estimated from thermoluminescent dosimeter (TLD) measurements. We used TLD chips (TLD-100, Harshaw Bircon) packed in groups of three. Packed TLDs were placed behind the left, middle, and right portions of the liver. The TLDs were sent to be read to Nagase Landauer and were calibrated with cesium-137 (137Cs) gamma rays. A TLD system model 2000B + D (Harshaw Bircon) was used for readout. The minimal detectable dose of the TLD system was 0.2 mSv. The absorbed doses at the three points on the skin of patients were calculated as shown in Appendix 1.
The doses to the radiologists were measured with electronic personal dosimeters placed on the chest outside a lead protector. We used DIS-1 (RADOS Technology Oy) as the dosimeter. The dose equivalents, Hp(0.07) and Hp(10) (in µSv), were calculated, considering the response of DIS-1 chambers for the effective photon energy according to the data provided by RADOS Technology Oy.
The height, weight, and body mass index of patients; total fluoroscopic exposure time; total number of digital subtraction angiographic frames; maximal skin doses to patients; and dose equivalents, Hp(0.07) and Hp(10), to the radiologists were compared between the two procedure groups with each angiographic unit.
The Mann-Whitney test was used for statistical analysis. A p value of less than 0.05 was considered to represent a statistically significant result. In the procedures using Innova 4100, we analyzed the relationship between the displayed dose–area products and the maximal skin doses to the patients by means of the Pearson's correlation coefficient (r).
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionAPPENDIX 1: Absorbed Doses...References |
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Exposure Dose for Procedures with Innova 4100
The maximal skin dose to the patients was 284 ± 127 mGy (range,
130–467 mGy). The skin doses to the patients were 100 ± 69 mGy at
the left portion of the liver, 259 ± 98 mGy at the middle portion of
the liver, and 256 ± 140 mGy at the right portion of the liver
(Table 3). The
Hp(0.07) and Hp(10) outside the protectors of the
radiologists were 62.8 ± 17.4 µSv (range, 25.6–93.2 µSv)
and 57.2 ± 17.3 µSv (range, 29.7–83.2 µSv),
respectively.
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Comparison of Two Procedure Groups with Each Angiographic Unit
There were no significant differences between the two groups in the height,
weight, body mass index of patients; total fluoroscopic exposure time; or
total number of digital subtraction angiography frames.
The maximal skin doses to the patients were significantly lower with Innova 4100 than with Advantx LCA (p < 0.0005). The average maximal skin dose to the patients during the procedures with Innova 4100 was about one fourth of that with Advantx LCA.
There were no significant differences in the Hp(0.07) or Hp(10) outside the protectors of the radiologists between the two groups.
Relationship Between Dose–Area Products and Maximal Skin Doses to Patients
The dose–area products and the maximal skin doses to the patients
correlated (r = 0.767) (Fig.
1). The regression equation is as follows:
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionAPPENDIX 1: Absorbed Doses...References |
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The maximal skin dose to the patients during the procedures using the new unit with the digital flat-panel system was about one fourth that using the unit with the conventional system. Several factors are thought to contribute to the dose reduction. First, the digital flat-panel detector has high detective quantum efficiency. Second, the system software uses real-time image information to optimize all digital image chain parameters, including X-ray technique and spectral filtration. Third, the combination of a high-opacity tube and filtration enhances dose efficiency.
The deterioration of the image intensifier of the conventional system may result in an increase in the patients' skin dose. However, the iris in the image intensifier of the conventional system used in this study had been adjusted at the time of its regular maintenance to fix the exposure dose. Therefore, deterioration of the image intensifier had little effect on the result.
Some investigators have evaluated the entrance skin dose to patients during TAE for HCC [10, 11]. The total skin entrance dose was 1,793.7 ± 739.1 mGy and 973 ± 681 mGy as determined by Iida et al. [10] and Ishiguchi et al. [11], respectively. They used a conventional system for angiographic imaging without a digital flat-panel system. In our assessment, the maximal skin dose to the patients was 1,068 ± 439 mGy using a conventional system, and it was not higher than the doses reported by those researchers. Therefore, the new system with a digital flat-panel system seems to decrease the exposure dose of the patients, although differences in the protocol of the procedure, angiography equipment, and methods of dosimetry probably affect the dose to some extent.
Enhancement of the thermoluminescent response at low photon energies is one of the main disadvantages of TLD. Only a few reports are available on the TLD-100 response at diagnostic X-ray energy [12–14]. According to the data of Muhogora et al. [13], the TLD response to diagnostic X ray of 33 and 48 keV as normalized to 137Cs gamma rays is about 1.15 and 1.25, respectively. The estimated effective photon energy of our X-ray devices was 32–43 keV. In our assessment, the correction factor relevant to the energy response of TLD was 1.21, and the result was consistent with the findings of Muhogora et al.
There were no significant differences in the Hp(0.07) or Hp(10) outside the protectors of the radiologists between the two procedure groups with either angiographic unit, in contrast to the significant differences in the skin absorbed doses to the patients. The difference in the additional filters used is thought to be one explanation, because the additional filters affect the spectral distribution of the primary photons and the scattered photons from the patients. However, it seems to be difficult to explain the marked differences in patients' exposure but absence of differences in the radiologists' exposure only by the spectral distribution. The differences in equipped protective elements (screen) and the positional relationship between the radiologists and the X-ray tube may be other reasons. Saida [15] developed protective devices attached to the angiographic apparatus and assessed their effectiveness for reducing operators' exposure during abdominal vascular interventional procedures. In that assessment, the operator's dose at the abdomen outside a lead protector using the attached protective devices was about 1% of that using no such devices. Including the effectiveness of attached protective devices, further studies are required to measure the magnitude and spatial distribution of the scatter.
The usefulness of the measurements of dose–area product has been evaluated in the literature [16–20]. There was a strong positive linear association between the maximal skin doses to the patients and the dose–area products. Therefore, the maximal skin dose to the patients can probably be estimated from the dose–area products during TAE for HCC. However, the difference in the X-ray equipment used and the kind of interventional procedures probably affects the regression coefficient. So, it is important to assess the relationship between the dose–area products and the maximal skin dose to the patient during each interventional procedure at each institution.
This study has some limitations. We compared the new angiographic unit with a digital flat-panel system used for 1 year and the conventional unit used for 7 years. The latest units without a digital flat-panel system will also reduce the patients' skin dose due to recent developments in dose-reduction techniques. However, as mentioned, the new angiographic unit with a digital flat-panel system reduced the patients' skin doses when compared with the doses noted in other recent articles [10, 11]. Therefore, it will be useful in dose reduction compared with the equipment generally used in recent times.
In conclusion, the new digital flat-panel system for angiographic imaging can reduce the patients' skin dose during TAE for HCC as compared with the conventional system.
APPENDIX 1: Absorbed Doses at Three Points on the Skin of Patients
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionAPPENDIX 1: Absorbed Doses...References |
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Advantx UNV (GE Healthcare) was used as the angiography equipment.
Irradiation conditions were based on the following protocol: 80-kVp tube
voltage, 400-mA tube current, and 12-inch (30 cm) image intensifier size. As a
phantom, we used Tough Water Phantom WE type (Kyoto Kagaku) with a 20.0-cm
thickness. We placed a calibrated ion chamber (model 9010, Radcal) at the
center of the exposure field on the lower surface of the phantom. The TLD
chips packed in groups of three were also put in the center of the exposure
field in contact with the ion chamber. Then, irradiation was done taking 625
digital subtraction angiography frames. The absorbed dose of the ion chamber
was 1.28 Gy, and the average Hp(0.07) measured by the TLD was 1.88
Sv. The coefficient factor (CF) was calculated by the following
equation:
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Acknowledgments
We thank Shinju Funaki for his advice and expertise.
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionAPPENDIX 1: Absorbed Doses...References |
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