Two different head and neck protection devices were evaluated (Fig. 1). The head protector (HeadPeaceTM,Texray AB, Sweden), with 0.25 mm lead equivalence, is designed to provide radiation protection in the upper section of the head. The extended thyroid protector (MindPeace™, patent pending, Texray AB, Sweden) evaluated in this study was a prototype of 0.5 mm lead equivalence, extended in the front and on both sides, and designed to provide radiation protection in the lower and middle sections of the head.
Thermoluminescent dosimeters (TLD) DXT-RAD Ringlets TLD-100 (Thermo Fisher Scientific Inc), calibrated for Hp (0.07) according to ISO 4037-1,-3, were used to measure ionizing radiation (13).
Figure 1. A the head protector used in both the phantom study and the clinical study and B, the extended thyroid protector used in the phantom study.
Phantom study
To study exposure to the head and neck, a study setup was developed to simulate a radiologically guided intervention. An anthropomorphic phantom, head, and thorax, (Rando Alderson, USA) was used to simulate a medical practitioner, exposed to scattered radiation. In the phantom head, TLDs were positioned at different depths in five slices (a, b, c, d and e), as shown in Fig. 2. Each slice was 5 cm apart, and in between each slice a 2 mm high polymethyl methacrylate (PMMA) slice was inserted, drilled with holes for placement of TLDs. In the head protector and ceiling mounted lead shield studies all TLD position were used while for the extended thyroid protector the TLD position 1–14 were used, (Fig. 2). The thorax phantom part, was equipped with a radiation protective apron of 0.5 mm lead equivalence.
Figure 2. Illustration of the phantom used to simulate the operator’s head where TLDs were positioned at different depths in five slices (a, b, c, d and e). For the head protector and ceiling mounted lead shield studies all TLD positions (light grey and dark grey) were used, while for the extended thyroid protector study the TLD positions 1–14 (dark grey) were used. On the right, slice c is shown enlarged, illustrating the numbering in each individual section.
Another phantom was placed on a table to simulate a patient undergoing an x-ray examination. The x-ray equipment was positioned with the x-ray tube beneath the table set at zero-degree angle. The operator-phantom was placed facing the table, with the exposed area of the patient-phantom to the left, as shown in Fig. 3, imitating a typical exposure situation during x-ray guided interventions, with scattered radiation hitting the operator on the left side from beneath. During the evaluation of the head protector, four 5 cm PMMA blocks were used to simulate a patient (20x30x25 cm) and during the evaluation of the extended thyroid protector, a 21 cm thick anthropomorphic phantom was used. Exposure-parameters are presented in Table 1.
Figure 3. A schematic phantom set-up to illustrate a medical practitioner performing a radiologically image-guided procedure. Figure 3A shows the measurement setup seen from the foot end of the patient phantom and Fig. 3B the measurement setup seen from the left side of the patient phantom, See Table 1 for details.
Table 1
Exposure-parameters for phantom study. * Siemens Artis Q (Siemens Healthineers, Germany) angio system. ** Philips MultiDiagnost Eleva FD (Philips, The Netherlands). ***Dose Area Product, to terminate the radiation at the same exposure-level
Parameters | Head protector and ceiling mounted lead shield | Extended thyroid protector and standard thyroid collar |
Modality | Siemens Artis Q* | Philips Multi Diagnost Eleva FD** |
Table height (cm) | 90 | 80 |
Operator phantom height, h (cm) | 165 | 165 |
Central beam axis - operator phantom front distance, d (cm) | 26 | 25 |
Central beam axis - operator phantom side distance, s (cm) | 58 | 66 |
Protocol | Abdomen | Abdomen |
Exposure mode | Acquisition | Acquisition |
Zoom (cm) | 42 | 48 |
Source image distance | 120 | 125 |
Patient phantom surface - detector distance, y (cm) | 50 | 54 |
Frames per second | 4 | 2 |
Tube voltage (kV) | 70 | 90 |
Tube load (mAs) | 30 | 25 |
Filter | No | 1 mm Al, 0.1 mm Cu |
DAP*** (Gycm2) | 400 | 130 |
Evaluation of the head protector and extended thyroid protector
To evaluate the radiation shielding effect of the protectors, a shielding-effect ratio, RSE, was developed for every measuring point in the head phantom, comparing the TLD-signal, including the radiation protection, with the TLD-signal without the evaluated radiation protection, where RSE=1-[Hp(0.07)shielded/Hp(0.07)unshielded)].
For evaluation of the head protector, the PMMA slices in the head phantom (b-e) were prepared with 224 TLDs (53, 57, 59 and 55 TLDs per slice. As comparison a ceiling mounted lead shield with 0.5 mm lead equivalence was used. Meanwhile for the evaluation of the extended thyroid protector, the PMMA slices in the head phantom (a-e) were prepared with 70 TLDs (14 per slice). As comparison, a prototype of a standard thyroid collar, with 0.5 mm lead equivalence, of the same attenuating material as the extended thyroid protector used in this study, was evaluated. The dose-area-product (DAP) indication on the x-ray equipment was used to terminate the radiation at the same exposure-level between set-ups.
Clinical study
The clinical study was performed at two sites, Cork University Hospital (Cork, Ireland) and Sahlgrenska University Hospital (Gothenburg, Sweden). Fourteen study participants representing Cardiac, Cardiac Electrophysiology, Hybrid OR and Gastrointestinal Radiology departments were included. Each participant used the head protector in clinical practice during a period of thirty days. The participants followed usual radiation-protection routines in their respective departments and the head protector was used as complimentary personal protection equipment. TLDs were placed in 16 lining pockets inside and outside of the attenuating material, in a specifically modified head protector to enable evaluation of the shielding effect, (Fig. 4).
Figure 4. Illustration of the TLD-pocket positions. Positions marked black are on the outside of the head protector and positions marked white are on the inside of the head protector.
To estimate the absolute personal dose equivalent, a background subtraction was performed, using the mean TLD-signal from dosimeters placed in the inside and the outside lining pockets of a separate head protector placed in an office at each department during the measuring period.
The personal dose equivalent was compared between the inside and outside of the head protector to get a shielding effect ratio, i.e. RSE=1-[Hp(0.07)shielded/Hp(0.07)unshielded)]. No background subtraction was performed when calculating the shielding effect.