This study reports detailed dosimetric data from diagnostic angiographies performed in patients with spinal dural AVFs. The mean procedural DAP of 62 spinal angiographies performed in 25 patients was 260 Gy cm2, with a mean fluoroscopy time of 19.6 min and a mean volume of contrast material of 143 ml. As our local DRL, we propose 329.41 Gy cm2.
Spinal endovascular procedures, whether diagnostic or therapeutic, are frequently associated with a higher amount of radiation exposure compared to most intracranial fluoroscopically guided procedures. This is not only because of the difference in vascular anatomy but also the comparably larger volume and thickness of body parts being imaged [1]. Furthermore, complete spinal DSA, which is sometimes required to pinpoint the fistula location, entails selective catheterization of numerous segmental arteries in the neck, chest, abdomen and pelvis branching from various vessels. This may yield longer fluoroscopy times and the use of a larger volume of contrast material.
According to the literature [4,5,6] a high-resolution contrast-enhanced MRA of the spine may be helpful in locating the fistula site and consequently limit the angiographic effort. Luetmer et al. observed that MRA depicted a fistula in 20 of 22 patients presenting with an SDAVF. Only 14 cases had the level of the fistula included in the imaging volume, and in 13 (59%) cases the level and site of the fistula could be predicted within 1 vertebral level, resulting in a more than 50% decrease in fluoroscopy time and contrast agent volume [4].
Using preangiographic ceMRA, the level of the fistula was accurately detected in 16/25 (64%) of the patients in the present series; however, in preoperative angiographies no significant difference between MRA positive and MRA negative cases was found in terms of DAP, fluoroscopy time or contrast agent volume. This might be explained by the small population size, the angiographers’ various degrees of expertise and the unique technical challenges of each case.
SDAVFs may arise anywhere between the foramen magnum and sacrum. Krings et al. stated that in their experience more than 80% of all SDAVFs are located between the Th6 and L2 vertebral levels [2]. Likewise, in our study 17 fistulas (17/25, 68%) were detected between those levels.
Regarding preoperative angiographies, we found no significant difference between fistulas at common and uncommon levels in terms of procedure DAP and contrast agent volume; however, the mean fluoroscopy time was significantly higher in the group of fistulas found at uncommon levels (42.7 min versus 28.5 min), which is consistent when considering the angiographical routine workflow. If the preangiographic MRA is negative, as is the case with most of the fistulas at uncommon locations, we usually begin with selective catheterization of segmental vessels at the thoracolumbar junction and move on to sacral or upper thoracic segmental arteries if necessary. As a result, a longer fluoroscopy time is commonly required to locate the fistula in these cases; however, because the DAP of pulsed fluoroscopy is relatively low as compared to a DSA run, a longer fluoroscopy time does not necessarily imply a significantly increased radiation dose.
In the literature, radiation dose data from spinal diagnostic angiographies were commonly published from cohorts with heterogeneous pathologies [1, 4, 10,11,12, 14]. In contrast, we rather aimed to collect homogeneous data dedicated to a specific spinal vascular pathology. For example, Chen and Gailloud analyzed 302 consecutive spinal angiograms conducted in 288 patients over a 10-year period [11]. Only 25 patients (42%) in this collective had dural AVFs. The majority (95%) of angiograms were full spinal angiographic examinations. The average contrast amount was 110 ml and the fluoroscopy time 25 min. These values are comparable with those of our complete cohort (n = 62; contrast agent 143 ml, fluoroscopy time 19.6 min); however, Chen and Gailloud neither undertook any subgroup analysis nor presented data on radiation dose. Instead, they focused on procedure safety in terms of neurologic and systemic complications. In another study, Luetmer et al. reported a mean fluoroscopy time of 38 min and a mean volume of contrast agent of 219 ml in their series of preoperative spinal angiograms performed in 22 patients with SDAVFs [4]. These findings are consistent with our results from preoperative angiographies, with a mean fluoroscopy time of 33.1 min and a contrast agent volume of 232 ml.
Spinal vascular malformations can easily be overlooked on DSA, hence repeat angiography is not unusual. According to Gailloud, common factors are e.g. misinterpretation of segmental arteries, demonstration but not perception of lesions, unintentionally missing the level of the feeding vessel, deliberate limitation of the procedure (e.g., no pelvic injections) and poor or nonselective injections [14]. Moreover, excessive patient discomfort caused by prolonged examinations represents a common reason for the angiography being terminated early. If an initial study is negative, Gailloud et al. believe that the threshold for seeking a second view and/or repeat the angiography should be low [14]. Likewise, in five of our patients the fistula was eventually detected on the second preoperative angiography.
The ICRP (International Commission on Radiological Protection) and the European Directive 2013/59/EURATOM directives underline the need for justification of patient exposure to radiation and highlight the importance of both documenting the radiation dose of each examination and utilizing appropriate diagnostic reference levels [7, 8]. Institutions or individual practitioners gather radiation dose reports for a procedure performed in their own practice to use reference levels as a quality improvement tool. For the determination of local DRLs with acceptable 95% confidence intervals, Miller et al. proposed at least 30 studies of the same procedure [1].
The National Federal Office of Radiation Protection has not yet established a national DRL for spinal endovascular procedures [9]. Moreover, a dedicated literature query did not reveal officially established or recommended DRL for spinal angiographies in further European countries, the USA, South Korea or Australia [15,16,17].
Recently, Opitz et al. suggested a DRL for spinal angiographies performed in patients presenting with SDAVF. They presented dosimetric data for SDAVFs from 58 diagnostic spinal angiographies, revealing a DRL of 396.39 Gy cm2 [18], which is in line with our calculated values. Furthermore, two multicenter studies from France done by Etard et al. and Kien et al. reported DRLs for spinal angiographies [19, 20]. They included 123 and 171 spinal angiographies from various centers in France and proposed a DRL of 185 Gy cm2 and 483 Gy cm2, respectively; however, a pathology-based subgroup analysis was not carried out in their studies, disabling a reasonable comparison with our findings.
Our study has several limitations because of the monocentric design. Angiographies were performed using a single angiographic system from a single vendor (Siemens Healthineers). Furthermore, we only analyzed diagnostic spinal angiographies of SDAVFs, hence the provided dosimetric data cannot be generalized to other spinal endovascular procedures and pathologies; however, since dural AVFs are the most prevalent indication for a spinal angiogram, our data may be considered as guidance and cover the vast majority of patients undergoing this procedure. Finally, the dosimetric values provided in this study are not weight-corrected.