The mean total DAP value of TACE reported in the present study (165.2 Gy·cm²) was smaller than those of the previous studies performed to set the diagnostic reference level (216–395.3 Gy·cm²) [10–12, 20], and was comparable with those of studies reporting radiation dose of CBCT-guided TACE (149.8–319.0 Gy·cm²) [17, 18, 21]. In several studies comparing new and old angiography systems when performing TACE, low median DAP values of new angiography systems were reported, which are lower than that those reported in the present study (145.3 vs. 57.4–132.9 Gy·cm²) [7, 14, 15]. In terms of fluoroscopy time, our results were similar to those reported in the literature (19.1 vs. 15.6–19.8 min) [10, 12, 18–20].
In the present study, we were able to suggest several risk factors for high DAP during TACE, and possible explanations for them are as follows. First, a high BMI was a significant predictor of high DAP, which can be explained by the increased thickness of the patient within the radiation field [22]. The automatic exposure control installed in modern angiography units automatically controls the radiation beam quality regarding tube potential, tube current, and thickness of additional filters in response to the patient's thickness to reduce the radiation dose while maintaining the image quality [23, 24]. Second, sex differences in body shape, particularly the shape of the abdomen, may also have contributed to the difference in total DAP between men and women [25]. Third, in cases of large (> 3 cm) tumors, the total DAP tended to be higher, probably because of the multiple feeding arteries that should be catheterized individually to be treated (Table E5 [online]. Finally, in the presence of aRHA or aLHA, additional DSA and CBCT are usually performed at the aberrant hepatic artery for the complete evaluation of the hepatic arterial supply, thereby increasing total DAP values.
It is more complex to explain the risk factors for each radiation source (fluoroscopy, DSA, and CBCT) because CBCT and DSA can play a complementary role in guiding microcatheters and micro-guidewires during TACE [17, 26, 27]. CBCT can help detect small tumors and provide the three-dimensional anatomy of the feeding arteries, replacing multiple DSA acquisitions and aiding superselective TACE [17, 26–28]. In the practice pattern of our institution, most superselective TACEs were performed after performing CBCT, while many of the nonselective TACEs were performed with or without minimal CBCT examination. Therefore, non-selective TACE may be associated with increased DSA DAP and decreased CBCT DAP. In addition, because a large proportion of fluoroscopy time is usually used to guide selective catheterization, fluoroscopy DAP is likely to be decreased in non-selective TACE [11, 20]. HCC with PVTT is known to be associated with increased tumor burden, infiltrative tumor type, and decreased hepatic function [29–31]. In this study, patients with Child-Pugh class B were more likely to have PVTT and undergo nonselective TACE, which is also associated with a smaller number of selectively treated vessels (Table E2 and E3 [online]).
The presence of aRHA and aLHA were significant predictors of high DAP. Anatomical variation of the hepatic artery is frequently observed, and the prevalence values of aRHA and aLHA have been reported to be 10.8–21.6% and 15.9–19.0%, respectively, in the literature [32–36]. In the present study, the prevalence rates of aRHA and aLHA were 14.3% and 14.5%, respectively. To completely evaluate the hepatic parenchymal lesion and detailed segmental hepatic artery anatomy in patients with aberrant hepatic arteries, additional DSA and CBCT performed at the aberrant hepatic artery are usually required. In this study, the impact of the presence of aLHA on the total DAP was more significant than that of aRHA. The presence of aLHA was a significant predictor of high DAP of DSA and fluoroscopy, whereas aRHA was not. Possible explanations for this result, considering the practice pattern in the authors' institution, are as follows: As described in the Methods section, we routinely performed SMA angiography in the initial session of TACE to evaluate the anatomical variation of the celiac axis and hepatic arteries. In most cases, aRHA and its supplying liver parenchyma were well evaluated in SMA angiography; therefore, additional DSA at aRHA was not required. However, when we performed celiac or CHA angiography, LGA originating from the proximal segment of the celiac axis was not completely evaluated. In patients with aLHA originating from the LGA not optimally evaluated on celiac angiography, we performed additional selective angiography using a microcatheter, consequently increasing DAP from DSA. Regarding fluoroscopy DAP, in our experience, catheterization of the LGA using a microcatheter tended to be more difficult and time-consuming than the catheterization of the aRHA arising from the SMA.
Different DAP values can also result from the use of different angiography systems. Several studies comparing the new and old angiography systems have reported significantly different DAP values between the two systems [7, 14–16]. In addition, when compared with the results using Allura Xper FD20 (control group; Philips Healthcare, Best, the Netherlands) reported by Schernthaner et al. [14], our results showed a higher CBCT DAP per examination (median: 69.2 vs. 16.5 Gy·cm²) and a lower fluoroscopy DAP per minute (median: 2.4 vs. 6.4 Gy·cm²), thereby reflecting the difference between angiography systems and settings. Although two different angiography units were used in the present study, the difference in total DAP was not statistically significant.
The present study has limitations because it was conducted in a single institution using only the angiography units of a specific manufacturer. The preferred technique and methods of TACE may vary between operators, institutions, and countries, which may also affect the radiation dose during TACE. Although this study included a large number of patients, the generalization or application of our results to individual institutions requires caution.
In conclusion, we were able to provide detailed reports on radiation doses during TACE and the risk factors for high radiation doses.