| Περίληψη: | Radiation exposure during endovascular repair of abdominal aortic aneurysms (AAAs) is a potential issue. Several studies have identified factors affecting radiation exposure, although they are limited. The aim of the present Thesis was to identify independent factors affecting radiation exposure in patients undergoing standard endovascular aneurysm repair (EVAR). Forty–eight consecutive patients underwent elective EVAR for infrarenal AAA managed between April 2019 and April 2020. Fluoroscopy time (FT) and kerma–area product (KAP) were the main outcome measures. Median (interquartile range) FT and KAP values were 1018 (653 – 1619) s and 2.68 (2.08 – 3.81) mGym2, respectively. C3 Excluder stent–graft use and main body insertion site from the right femoral were associated with significantly lower FT. Coronary artery disease, endografts with two docking limbs, AAA diameter, neck angle and length, procedure duration, contrast amount, and hospitalization were associated with significantly higher FT. Neck angle was the single independent perioperative factor related to FT higher than the median value observed in the study (P = 0.004, odds ratio: 1.073, 95% confidence interval: 1.023 – 1.126). The use of the C3 Excluder device was associated with lower KAP. AAA diameter, neck angle, procedure duration, contrast medium amount and postoperative hospitalization were associated with higher KAP. AAA diameter was the single independent factor related to KAP higher than the median value observed in the study (P = 0.013, odds ratio: 3.73, 95% confidence interval: 1.32 – 10.56).
Additionally, the current Thesis aims to evaluate patient doses and establish institutional diagnostic reference levels (IDRLs) during fluoroscopically–guided EVAR procedures. FT and KAP were recorded from 87 patients that underwent EVAR with a mobile C–arm fluoroscopy system. Effective dose (ED) and organs’ doses were calculated utilising appropriate conversion coefficients based on the recorded KAP values. Entrance surface dose (ESD) was calculated based on KAP values and technical parameters. The mean FT was 22.7 min (range 6.4 – 76.8 min), resulting in a mean KAP of 36.6 Gycm2 (range 2.0 – 167.8 Gycm2), a mean ED of 6.2 mSv (range 0.3 – 28.5 mSv) and a mean ESD of 458 mGy (range 26 – 2098 mGy). The corresponding median values were 17.4 min, 25.6 Gycm2, 4.4 mSv and 320 mGy. The threshold of 2 Gy for skin erythema was exceeded in two procedures for a focus–to–
skin distance (FSD) of 40 cm and six procedures when an FSD of 30 cm was considered. The highest doses absorbed by the adrenals, kidneys, spleen and pancreas and ranged between 3.7 and 313.3 mGy (average 66.8 mGy), 3.3 and 285.1 mGy (average 60.8 mGy), 1.3 and 111.1 mGy (average 23.7 mGy), 1.1 and 92.1 mGy (average 19.6 mGy), respectively. The IDRLs established at the 3rd quartile (75th percentile) of the distribution of the KAP values and are equal to 40.6 Gycm2. A wide range of patient doses was reported in the literature. The radiation dose received by the patients was comparative or lower than most of the previously reported values. However, higher doses can be revealed due to the X–ray system’s non–optimum use and extended FTs, mainly affected by complex clinical conditions, patients’ body habitus and vascular surgeon experience. The large variation of patient doses highlights the potential to optimise the EVAR procedure by considering the balance between the radiation dose and the required image quality. Additional studies need to be conducted in increasing the vascular surgeons’ awareness regarding patient dose and radiation protection issues during EVAR procedures.
Furthermore, the present Thesis describes the first series of patients with a AAA, including two patients with a juxtarenal aneurysm, treated with the ALTOTM abdominal stent–graft system (Endologix Inc, Irvine, Calif). The ALTOTM abdominal stent–graft system (Endologix Inc, Irvine, Calif) is the last–generation, polymer–based device for treatment of patients with AAAs. Six men were treated with the ALTOTM device at a single public center. All procedures were uneventful, while the dosimetric results recorded, in terms of kerma–area product and fluoroscopy time, were similar to those of previously published studies. No endoleak of any type was observed while there were no cases of device migration, thrombosis or structural graft failure at the first postoperative follow–up after one month. This clinical series demonstrated that the use of the ALTOTM stent–graft system is associated with promising patient outcomes. Lifelong post–surgery imaging surveillance may highlight possible late failures and suggest potential graft improvements.
The effect of body–mass–index (BMI) on organ doses (ODs) during infrarenal EVAR procedures was also evaluated. Patient– and intra–operative data from fifty–nine EVAR procedures were inserted into VirtualDose–IR software to calculate ODs. For overweight, obesity class–I and obesity class–II, ODs were up to 147%, 412% and 775% higher than those for normal weight patients, respectively. A large variation was observed in ODs published in literature mainly due to the differences in the software and the technical parameters used for the calculations.
The last objective of this Thesis was to document FT during EVAR procedures and identify possible factors that influence it. A retrospective analysis of a 180 patients' database with infrarenal AAAs submitted to EVAR during a seven–year period was performed. The FT was evaluated regarding risk factors and comorbidities, graft type, and patient–related, clinical and technical parameters. FT's median (interquartile range) was 1011 (698 – 1500) s. Excluder and C3 Excluder were associated with significantly lower FT values when compared to other grafts. Hypertension, dyslipidemia, age ≥ 70 years, maximum aneurysm diameter ≥ 6 cm, and procedure duration ≥ 2 hours resulted in higher FT values. A significantly lower FT was found for the operations performed in the seventh year of the study’s period compared to the previous six years, mainly due to the use of Excluder or C3 Excluder grafts. However, these grafts did not show any significant difference in FT values during the seven years. A significant correlation between FT with age and procedure duration was found. Nevertheless, procedure duration is a poor FT predictor in linear and logistic regressions, although is significantly correlated with FT. Dyslipidemia, procedure duration and graft type are independent predictors of FT larger than the median, while only the procedure duration is a predictor for FT larger than the 75th percentile value. The identified factors regarding radiation protection issues should be considered when contemplating AAA repair, however, without compromising the procedure's efficacy.
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