Patient dose measurement
Fifty-seven patients underwent therapeutic ERCP. This prospective study was conductedat Larissa University hospital, Greece. Clinical indications for the investigation of ERCP are presented in . The ethics and research committee approved the study and a written consent was obtained from all patients prior to the procedure. Thermoluminescent dosemeters (TLDs) were packed on a thin envelope made of transparent plastic foil, to protect them from any contamination. Each envelope contained three TLDs. Three envelopes were used to measure the ESD, exit dose and thyroid surface dose accurately for each patient. It was important to determine the exit dose as it reflected the transmission of the radiation and the radiation dose to the interior organs. During the procedure, the TLDs were kept in the required positions (entrance of the radiation [at intersection point of the X-ray beam axis with the entrance surface of the patient], exit of radiation and thyroid gland) and were stuck in place with adhesive tape. The operators performed the investigations as their daily practice with a protocol that is designed to minimize patient and examiner exposure.[17
The data recorded for all procedures included patient body characteristics (age, sex, height, weight and body mass index (BMI) (weight/height 2), tube voltage (kV), tube load (mAs), and fluoroscopic data: kV, tube current (mA), total screening time, clinical indication, start and end time.
Staff dose measurement
Two experienced gastroenterologists (more than three thousands procedures) performed all the procedures. Regarding gastroenterologist, the radiation dose was monitored using three TLDs packed on a thin envelope made of transparent plastic foil and were stuck in place with adhesive tape, at four sites: the forehead, thyroid, chest, and left hand. The staff used a 0.25 mm lead equivalent thick apron, full wrap-around protection (Dr. Goos-Suprema GmbH, Heidelberg, Germany). The assistant used 0.50 mm lead equivalent thickness, frontal protection (Rheix-srl, Milan, Italy). TLDs were packed on a thin envelope made of transparent plastic foil, to protect them from any contamination. Each envelope contained three TLDs. TLDs were attached outside the lead apron at the chest level and at the left hand of the assistant. Neither a protective eyeglass nor thyroid collar were worn by either of the staff. The examiner radiation dose in gastroenterology departments is routinely monitored by TLD dosemeters.
During the procedure, the first examiner stood on the right side of the typical position of the patient. A lead barrier (100 × 60 cm2) of 0.50 mm lead equivalent was placed on the side of the gastroenterologsit to reduce radiation scatter to the examiners standing to the side of the fluoroscopy couch.
The assistant, who controlled the radiation exposure, stood on the right side of the first examiner. All procedures were performed with the examiners at the same locations . The nurses remained outside the X-ray room during the exposure; therefore, there was no need for radiation dose measurements.
Patient setup, lead apron and examiners positions during ERCP examination. 1. Gastroenterologist; 2. assistant gastroenterologist; M1., endoscopic monitor; M2. fluoroscopic monitor. T1 X ray tube. T2,Table, and L lead apron
ERCP was performed with a duodenoscope (Olympus, exera CLE 145(Olympus Medical System Corp, Japan)). The patient was placed on an X-ray couch in the left anterior oblique position with right leg flexion.
During the procedure, radiographic and fluoroscopic images were obtained after injection of contrast medium. Since the contrast medium normally remained in the biliary tree for several minutes following removal of the duodenoscope, a post procedure anteroposterior projection was also obtained, if required, for further evaluation of the stent placement or residual stones.
Entrance surface dose (ESD) was made by attaching a sachet containing four thermoluminiscent dosemeters (TLDs) to the patients’ skin on the central axis of the X-ray beam. The lithium fluoride TLD chips (TLD-100) were used for patient dose measurements while calcium fluoride was used for staff dose measurements for their numerous advantages.[18
] The read-out of TLD dosemeter was made using a manual TLD reader (Harshaw 3500, Solon, USA). The overall system performance was checked before any reading session. The read-out was at a 10°C preheat temperature and the signal was acquired from 100 to 280°C with heating rate of 100°C s-1. Prior to each irradiation, all dosemeters were annealed (as recommended by the manufacturer) in annealing oven (TLDO, PTW, Freiburg, Germany) at 400°C for 1 h, followed by fan forced cool down to 1000°C which was held for 2 h in order to optimize its characteristics.
This study was performed using an overcouch X-Ray (Philips Diagnost 93) fluoroscopy machine. Total filtration of the X-ray beam was 4.0 mm Al. The machine had an option of selecting pre-programmed exposure factors based on the type of examinations performed. Personnel involved in operating the machine could also manually change the pre-programmed exposure factors. The machine also had the option to capture the last fluoroscopic image.
Estimation of absorbed organ doses and effective doses
ESD was used to estimate the organ equivalent dose (H
) using software provided by the National Radiological Protection Board (NRPB-SR262).[19
] It contains the results of modelling conditions of exposure relevant to 68 common radiographic views. For each view, normalized doses are presented for 26 organs or tissues.
However, as specific projections were not available for ERCP in the aforementioned software, organ doses (mGy) were obtained from the average value of the conversion factors for the most similar projections, i.e PA kidney, stomach and oblique duodenum views.
The organ equivalent dose (mSv) is given by:
Where DT, R
is the mean absorbed dose to tissue (T) from radiation (R) and wR
is the radiation-weighting factor.[5
Effective dose (E, mSv
) is a quantity that has been introduced to give an indication of risk from partial or non-uniform exposure in terms of the equivalent whole body exposure which gives the same risk.[4
Where HT is the equivalent dose to tissue T.
The examiners’ E
can be estimated by using the following formulae[20
Where HOS is the dose measured by the dosemeter at the neck (shallow depth) and HU is the dose measured by the dosemeter under the apron at waist level (deep). In a case of single dosemeter worn at collar level, usually, HU = 0.01 HOS, therefore, the effective dose can be approximated as:
Cancer risk estimation
The risk (RT
) of developing cancer in a particular organ (T) following ERCP after irradiation was estimated by multiplying the mean organ equivalent (HT
) dose with the risk coefficients (fT
) obtained from ICRP.[4
The overall lifetime mortality risk (R) per procedure resulting from cancer/heritable was determined by multiplying the effective dose (E) by the risk factor (f).
The risk of genetic effects in future generations was obtained by multiplying the mean dose to the ovaries by the risk factor.[3
Statistical analysis used
All values of radiation dose were expressed as mean, median, minimum, third quartile and the maximum values are presented due to the asymmetry in data distribution.