Benign prostatic hyperplasia (BPH) is an exceedingly common condition, estimated to affect greater than 50% of men over the age of 60. Typical patient concerns involve the lower urinary tract and include pain, incontinence, urgency, and a weak stream. In severe cases, the compression of the urethra by the prostate can result in urine retention, reflux and eventually acute renal failure. Prostatic artery embolization (PAE) has emerged as a popular alternative to conventional methods for treatment of symptomatic prostate enlargement. This minimally invasive procedure offers many advantages, most notably a reduction in recovery time and risk of urinary and sexual side effects compared to surgical resection. However, it is a technically complex and time-consuming procedure, factors which contribute to relatively high radiation doses incurred by both the patient and Interventional Radiologist.
There are several related but distinct terms which may cause confusion when discussing radiation dose measurement. Absorbed dose refers to the amount of energy deposited by ionizing radiation. Because there are various forms of radiation, each with differing properties, the equivalent dose is calculated with weighted coefficients to estimate the level of biological damage. During medical procedures, radiation is delivered in the form of X and gamma rays, which have a coefficient of 1, so absorbed and equivalent dose are equal. Finally, effective dose (E) takes into account the sensitivity of the particular organ or body part to radiation, as dividing tissues are more susceptible to damage and is used to estimate the potential long-term effects of radiation exposure. Absorbed dose is measured in Gray (Gy) while effective dose and equivalent dose are measured in Sievert (Sv).
This study prospectively analyzed radiation exposure to both patients and interventional radiologists during 25 prostatic artery embolization procedures .
Study Population and Treatment Protocol
Beginning in August 2015, twenty-five patients received PAE to address lower urinary tract symptoms resulting from BPH. The average age was 65.7 (range 43-85) with an average prostate volume of 79 cm3(range 36-157, > 30 suggests BPH) and average prostate-specific antigen level of 5.9 ng/mL (> 4 is considered abnormal.)
All procedures were performed by a single interventional radiologist. Fluoroscopy was performed at 15 images per second, digital subtraction angiography (DSA) was performed at 2 images per second with standard aortic protocol and Cone-Beam CT was available. All procedures were performed under only local anesthesia, another advantage compared to traditional surgery. Embolizations were completed using 100-200 um nonspherical polyvinyl alcohol particles (Cook) or 400um polyzene-coated hydrogel microspheres and the endpoint was complete occlusion of the prostatic artery as indicated by reflux of contrast. After each procedure, the fluoroscopy time, Dose-Area Product (DAP: absorbed dose x area irradiated), number of images obtained, and irradiation parameters for DSA, fluoroscopy, and cone-beam CT were recorded.
To evaluate Peak Skin Dose (PSD) delivered to patients, a radiochromic film was positioned under the patient’s pelvis, the expected site of highest radiation delivery, and assessed following the intervention. In all the encounters, the Interventional Radiologist wore a standard leaded apron and neck collar but did not use leaded glasses. To measure the dose absorbed by the Interventional Radiologist, 9 thermoluminescent dosimeters were placed: neck collar (over the lead,) on the chest (under lead apron,) on the glabella, as well as on each eyebrow, wrist, and foot. One additional dosimeter pair was carried to measure background radiation and identify contamination. The patient was further protected with a draped leaded screen, preventing radiation aimed at the pelvis from scattering upward to the torso and head. Effective dose to the physician was estimated using von Boetticher’s double dosimetry algorithm .
Bilateral PAE was technically successful in all patients. Average fluoroscopy time was 30.9 ± 9.5 min with a mean Dose-Area Product of 450.7 ± 182.7 Gy cm2. These values are similar to those for patients undergoing other complex image-guided procedures. DSA was responsible for 71.5% of the total DAP, followed by fluoroscopy (19.9%), and cone-beam CT (8.6%).
The mean patient PSD was 2,420.3 mGy (range, 1,390–3,616 mGy). Skin injuries such as transient erythema have previously been reported with doses greater than 2000 mGy, but there were no skin lesions detected within the three-month follow-up window. The average effective dose for the interventional radiologist was 17 μSv (range, 4–47 μSv), which is comparable to other high-exposure procedures .
Prostatic Artery Embolization has been shown to be beneficial in relieving lower urinary tract symptoms resulting from benign prostatic hyperplasia while being well tolerated with few side-effects. To date, there is limited available data on indirect measures of radiation doses during PAE and to the authors’ knowledge no published prospective data on direct measures. The authors concluded that PAE exposes both the patient and the radiologist to relatively high doses of radiation, with Digital Subtraction Angiography as the main source, consistent with findings in prior studies . However, the authors offer no strategies for limiting radiation dose nor remark as to whether this is possible or clinically necessary.
Current guidelines from the International Council on Radiologic Protections recommend an annual effective dose of no greater than 20 milli-Sv for occupational exposures, averaged over 5 years, with no single year exceeding 50 milli-Sv. With the average effective dose of 17 micro-Sv recorded in this study, a single Interventional Radiologist could theoretically perform in the realm of 1000 PAEs annually. Further sub-analysis of the individual dosimeters on the operator revealed an average micro-Sv of 213 on the neck (obtained over the lead) and only 8 on the chest (obtained under the lead.) This underscores the efficacy of the lead protective gear and indicates the majority of the operator dose is absorbed in the extremities away from vital organs, where clinical significance is thought minimal.
For the general public, suggested effective dose is less than 1 mSv per year averaged over 5 years. Unfortunately, while absorbed doses were calculated for each patient in this study, effective doses were not. But the wide individual differences in recorded absorbed dose between patients still did not result in any acute adverse event, let alone a dose-dependent one. Moreover, no compelling epidemiological evidence currently demonstrates significantly increased long-term cancer risks associated with levels of radiation exposure around 10 milli-Sv. Although this study offers no firms conclusions, the relative safety of radiation exposure is a consideration when counseling patients on the risks and benefits of PAE.
Written by Rei Mitsuyama, MS2, MD Student, Brown University
Edited by Thaddeus J Maguire, MD
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