Technical-Procedural Factors Influencing Radiation Dose in Prostatic Artery Embolization

Prostatic artery embolization (PAE) has become increasingly recognized as a minimally invasive solution for treating symptomatic benign prostatic hyperplasia (BPH). This procedure effectively merges satisfactory clinical outcomes with an impressive safety profile [1]. However, concerns have been raised regarding the associated radiation exposure for both patients and operators, primarily due to extended fluoroscopy times, multiple angiographic runs, and steep oblique projections [2,3]. In response to these concerns, various techniques have been developed to minimize radiation doses during PAE. For instance, intraprocedural cone-beam computed tomography (CBCT) has been utilized by certain groups to assist in the identification and selection of the prostatic artery, subsequently leading to decreased fluoroscopy time, fewer angiographic runs, and lower radiation exposure [4,5]. However, the benefits of this approach have faced scrutiny from other studies [6]. A low-dose angiographic protocol, which incorporates image processing to enhance lower image quality, has demonstrated a remarkable 74% reduction in radiation dose for the main operator during PAE compared to the standard protocol [7]. Despite this, large-scale studies reporting the use of such low-dose protocols in PAE remain limited. Additionally, the feasibility of conducting PAE using only anteroposterior imaging and intentionally unilateral PAE has also been suggested as viable strategies for minimizing radiation exposure [8,9]. Further research is essential to rigorously evaluate existing and innovative methods for reducing radiation exposure during PAE, ultimately identifying the most effective and practical solutions for integration into standard PAE practices.

This study reflects the recent experiences from a single center regarding the application of multiple techniques aimed at minimizing radiation doses during PAE. The primary goal is to evaluate these techniques and their efficacy in reducing radiation exposure. A secondary goal involves examining additional factors contributing to the total radiation exposure during PAE, while also reporting on the safety and effectiveness of PAE within the analyzed patient cohort.

Patient Selection Criteria for Prostatic Artery Embolization

Patients experiencing symptomatic BPH and treated with PAE at a single tertiary center between March 2020 and September 2021, with a minimum follow-up duration of two months, were retrospectively assessed. Inclusion criteria for the PAE procedure included: age ≥ 50 years, significant prostate enlargement (sonographically determined prostate volume exceeding 35 mL), moderate-to-severe lower urinary tract symptoms (International Prostate Symptom Score (IPSS) > 18), failure of medical treatment (5α-reductase inhibitors or selective α1-blockers administered for at least six months), and urinary retention managed through indwelling bladder catheter with at least three unsuccessful attempts at catheter removal prior to PAE. Exclusion criteria encompassed prior surgical or interventional prostate treatments, urinary tract infections, prostate or bladder malignancies, neurogenic bladder conditions, bladder diverticula larger than 3 cm, bladder stones, and any contraindications to angiography [10]. For all patients, computed tomography angiography (CTA) was carried out for treatment planning prior to the PAE procedure (Table 1).

All procedures were conducted using the same angiographic unit (Axiom Artis Zee, Siemens Healthineers, Erlangen, Germany) and by the same lead operator (with five years of prior experience in PAE).

Written informed consent was obtained from all patients prior to PAE, and the study received approval from the institutional research ethics review committee (approval number: 1950/2021).

Techniques Employed in Prostatic Artery Embolization

The fundamental techniques utilized in the current PAE study included the following procedures. Following local anesthesia, vascular access was secured via the common femoral artery using the Seldinger technique. A 4 or 5 French (F), 65-80 cm, reverse curve catheter (Cobra 1, Simmons 1, MOT, Merit Medical, USA, or Boston Scientific, USA) was employed to select the ipsilateral internal iliac artery (IIA) and facilitate the crossover maneuver. If catheterization of the contralateral IIA was unsuccessful with the same catheter, it was exchanged for a “vertebral” or “Bern” catheter. Digital subtraction angiography (DSA) of the IIAs was performed using the standard “Body” protocol of the equipment, with a manual injection of 10-20 mL of iodinated contrast through the angiographic catheter in anteroposterior and ipsilateral anterior oblique (30^o-40^o, often with additional caudal-cranial angulation up to 10^o) projections to document arterial anatomy and identify the origins of the prostatic arteries. Oblique roadmaps were created from the corresponding oblique DSAs (using the “DSA-Roadmap” function of the equipment) and were utilized to guide the catheterization of the prostatic artery; this was achieved using a microcatheter (1.7-2 F, Velout, Tellus, or Stridesmooth Asahi Intecc Co., Japan) and a double-angled 0.016-inch microguidewire (Meister-Asahi). Intra-arterial nitroglycerin was administered through the microcatheter to induce vasodilation, followed by acquiring DSAs with manual injections of 2-4 mL of contrast to examine the prostatic artery and its branches or anastomoses in detail. Embolization was performed until complete flow stasis was achieved using microspheres (Embosphere, Merit Medical, USA) with diameters ranging from 100-500 microns.

Subgroups of patients underwent modifications of the basic techniques, and the impact of these modifications on radiation dose was evaluated.

Application of Low-Dose Protocol for DSA Procedures

The preset LDP of the angiographic unit (Combined Applications to Reduce Exposure (CARE): Body CARE®-1 protocol, Siemens) is characterized by reduced pulse width and enhanced edge enhancement compared to the standard (“Body”) protocol (Figure 1).

Additional parameters for both the LDP and the standard protocol are accessible in Table 2.

For the purposes of this study, LDP was deemed successfully applied when all DSA images collected during a PAE procedure utilized this protocol.

Minimizing Oblique Projections in PAE

Oblique projections are essential for outlining the prostatic artery, particularly its origin; however, they also lead to significantly higher radiation exposure compared to anteroposterior (AP) views. A recently described technique [8] suggests that in cases with larger prostatic arteries and suitable anatomy, it is feasible to perform PAE using only anteroposterior fluoroscopy and/or DSA (AP-PAE). In this study, successful application of AP-PAE was determined when embolization of the prostatic artery on at least one pelvic side was achieved exclusively with AP projections. It is important to note that in modern angiographic systems, the X-ray generator is positioned beneath the table; hence, in a supine patient, the projections of AP-PAE are actually posteroanterior rather than anteroposterior. The acronym AP was deliberately chosen to avoid confusion with the prostatic artery acronym and maintain consistency with prior references to this technique.

Utilizing Roadmap Imaging Instead of DSA for Anatomical Demonstration

This approach, termed “RDMP-PAE” in this study, involves obtaining roadmaps after activating the “Roadmap” function, fluoroscopy, and manual contrast injection, instead of performing DSAs for all contrast injections through the angiographic catheter on both pelvic sides. This technique was also employed for specific superselective injections via the microcatheter, although a minimum of one DSA run per pelvic side was conducted pre- and post-embolization to enhance image clarity and ensure identification of smaller branches and anastomoses.

Employing Cone-Beam Computed Tomography (CBCT)

CBCT was used selectively to clarify arterial anatomy in cases where there was uncertainty based on pre-procedural CTA and intraprocedural DSA. For this purpose, “proximal” CBCT was conducted with 45 mL of iodinated contrast (diluted 50% with normal saline) injected into the IIA through the angiographic catheter at a rate of 5 mL/second after a four-second delay. In select instances, CBCT was performed to confirm the presence of small but potentially hazardous anastomoses between the prostatic artery and other arterial branches (such as vesical, rectal, and penile). This involved contrast injection performed distally through the microcatheter (“distal” CBCT), requiring manual injection of 3 mL of contrast (the same dilution as previously mentioned) at approximately 0.5 mL/second with a two-second delay. For both CBCT techniques, a five-second rotational scan covering 200° was employed (Table 2). Acquired images were processed using a dedicated workstation (Leonardo, Siemens) for three-dimensional reconstructions and maximum intensity projections.

Additionally, several techniques and parameters were consistently applied across all patients to minimize radiation exposure. All DSA runs were performed at a rate of one frame (fr)/second, while fluoroscopy was conducted at seven pulses (p)/second, reducing to 2-4 p/second during the embolic injection phase. During this critical phase, tight collimation was applied to focus solely on the prostatic area and potential anastomoses. No magnification was utilized during DSA runs, opting instead for the preset digital “zoom” function (×2) provided by the manufacturer.

Monitoring and Recording Radiation Dose in PAE Procedures

Following each PAE procedure, the total dose area product (DAP) (μGy‧m²) was recorded by the angiographic unit and extracted for further analysis. The dose length product (DLP) (in mGy‧cm) associated with pre-procedural planning CTA was also documented. The effective dose (ED) of CTA for each patient was calculated from DLP using a conversion factor of 0.015 mSv/(mGy‧cm) [11,12]. The ED for each individual PAE procedure was determined from DAP using the conversion factor specific to “Pelvic arterial embolization” (0.0026 mSv/(μGy‧m²)) [11,13].

Structured Follow-Up Protocol After PAE

Clinical evaluations and imaging follow-ups (transabdominal ultrasound) were scheduled at approximately three, six, and 12 months after PAE, subsequently occurring every six months thereafter. Changes in IPSS, prostate volume, and post-void residual (PVR) compared to baseline measurements were meticulously recorded. Clinical success was defined as achieving a post-treatment IPSS of ≤15 points, representing at least a 25% decrease from baseline, without necessitating additional treatments. For patients with indwelling bladder catheters, clinical success was also characterized by permanent catheter removal with spontaneous micturition and PVR < 100 mL.

In-Depth Statistical Analysis Methods

Descriptive statistics were computed for both quantitative and qualitative data. The normality of variables was evaluated through skewness, kurtosis, and the Shapiro-Wilk test. The four techniques under review (LDP, AP-PAE, RDMP-PAE, and CBCT) were analyzed for their influence on DAP using simple regression analysis, formatted as independent samples t-tests. The relationship between body mass index (BMI) and DAP was also assessed via simple regression analysis. Statistically significant factors affecting DAP were subsequently analyzed with multiple linear regression. To determine clinical success rates of PAE over time, the Kaplan-Meier method was employed. A p-value of <0.05 was considered statistically significant.

Overall Patient Demographics and Clinical Data

A total of 66 patients underwent PAE during the course of the study. However, seven patients were excluded (two due to the absence of follow-up data and five for reasons specified below). The baseline demographic and clinical data for the remaining 59 patients included in the analysis are summarized in Table 3.

Before undergoing PAE, 39 patients experienced moderate to severe lower urinary tract symptoms, whereas 20 had indwelling bladder catheters. Bilateral PAE was performed in 47 out of 59 patients (79.6%), while the remaining patients underwent unilateral PAE. For the 59 patients included in the study, the mean DAP recorded was 16,424.7 ±