Radiation protection measures: Implications on the design of neurosurgery operating rooms

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NEUROCIRUGÍA www.elsevier.es/neurocirugia

Clinical research

Radiation protection measures: Implications on the design of neurosurgery operating rooms夽 Pedro David Delgado-López a,∗ , Javier Sánchez-Jiménez b , Ana Isabel Herrero-Gutiérrez c , María Teresa Inclán-Cuesta c , Eva María Corrales-García d , Javier Martín-Alonso a , Ana María Galacho-Harriero a , Antonio Rodríguez-Salazar a a

Servicio de Neurocirugía, Hospital Universitario de Burgos, Burgos, Spain Servicio de Radiofísica, Hospital Universitario de Burgos, Burgos, Spain c Departamento de Enfermería de Neurocirugía, Hospital Universitario de Burgos, Burgos, Spain d Servicio de Oncología Radioterápica, Hospital Universitario de Burgos, Burgos, Spain b

a r t i c l e

i n f o

a b s t r a c t

Article history:

Objective: To describe pros and cons of some radiation protection measures and the impli-

Received 21 December 2017

cations on the design of a neurosurgery operating room.

Accepted 27 February 2018

Material and methods: Concurring with the acquisition and use of an O-arm device, a structural remodelling of our neurosurgery operating room was carried out. The theatre was enlarged, the shielding was reinforced and a foldable leaded screen was installed inside the

Keywords:

operating room. Radiation doses were measured in front of and behind the screen.

Radiation protection

Results: The screen provides whole-body radiation protection for all the personnel inside

Screen

the theatre (effective dose <5 ␮Sv at 2.5 m from the gantry per O-arm exploration; 0.0 ␮Sv

Shielding

received behind the screen per O-arm exploration; and undetectable cumulative annual

Operating room

radiation dose behind the screen), obviates the need for leaded aprons and personal dosime-

Sievert

ters, and minimises the circulation of personnel. Enlarging the size of the operating room

Oarm

allows storing the equipment inside and minimises the risk of collision and contamination. Rectangular rooms provide greater distance from the source of radiation. Conclusion: Floor, ceiling and walls shielding, a rectangular-shaped and large enough theatre, the presence of a foldable leaded screen, and the security systems precluding an unexpected irruption into the operating room during irradiation are relevant issues to consider when designing a neurosurgery operating theatre. ˜ ˜ S.L.U. All rights © 2018 Sociedad Espanola de Neurocirug´ıa. Published by Elsevier Espana, reserved.

DOI of original article: https://doi.org/10.1016/j.neucir.2018.02.007. Please cite this article as: Delgado-López PD, Sánchez-Jiménez J, Herrero-Gutiérrez AI, Inclán-Cuesta MT, Corrales-García EM, Martín˜ de quirófanos de neurocirugía. Neurocirugía. 2018;29:187–200. Alonso J, et al. Medidas de protección radiológica: implicaciones en el diseno ∗ Corresponding author. E-mail address: [email protected] (P.D. Delgado-López). ˜ ˜ S.L.U. All rights reserved. 2529-8496/© 2018 Sociedad Espanola de Neurocirug´ıa. Published by Elsevier Espana, 夽

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˜ Medidas de protección radiológica: implicaciones en el diseno de quirófanos de neurocirugía r e s u m e n Palabras clave:

Objetivo: Describir pros y contras de diversas medidas de protección radiológica y sus impli-

Radioprotección

˜ de un quirófano de neurocirugía. caciones en el diseno

Mampara

Material y métodos: Se realizó una reforma estructural del quirófano de neurocirugía a

Blindaje

propósito de la adquisición y uso de un O-arm. Se ampliaron las medidas y blindajes del

Quirófano

quirófano, y se instaló una mampara blindada y abatible en su interior. Se midieron dosis

Sievert

de radiación delante y detrás de la mampara.

Oarm

Resultados: La mampara proporciona una radioprotección integral para todo el personal de quirófano (dosis < 5 ␮Sv a 2,5 m del gantry por cada exploración con O-arm; 0,0 ␮Sv tras la mampara por cada exploración de O-arm; dosis acumulada anual tras la mampara, indetectable), obvia la necesidad de delantales plomados y dosímetros personales y minimiza ˜ del quirófano permite almacenar los la circulación de personal. El aumento del tamano equipos dentro y minimiza el riesgo de colisión o contaminación. Los quirófanos rectangulares permiten aumentar la distancia al foco emisor de radiación. Conclusiones: El blindaje de paredes, techos y suelos, la forma rectangular y la superficie lo más amplia posible, la presencia de una mampara plomada y abatible, y los sistemas de seguridad que impiden una irrupción inesperada en el quirófano mientras se está irradiando ˜ del quirófano de neurocirugía. son cuestiones relevantes a tener en cuenta en el diseno ˜ ˜ S.L.U. Todos © 2018 Sociedad Espanola de Neurocirug´ıa. Publicado por Elsevier Espana, los derechos reservados.

Introduction In current neurosurgical practice, procedures requiring the use of intraoperative radiological imaging are increasingly common, especially in spinal surgery.1,2 The imaging equipment emits ionising radiation with undesirable biological effects that are potentially harmful for patients, surgeons and all other operating theatre staff.3–6 Therefore, radiation protection measures are a basic need within the framework of a culture of safety and quality of clinical performance.7–9 Radiation protection in this context essentially depends on 2 factors: the use of individual radiation protection measures and the design of the facility. The latter is very important, as it will affect the entire useful life of the operating theatre and reduce or altogether prevent the need for other radiation protection measures which may be bothersome or even restrictive. The dimensions of the operating theatre, the thickness of the shielding and the location of the radiation sources are among the factors that influence the amount of radiation absorbed by patients and staff.2,8 As operating theatres must be increasingly multi-purpose and virtually all surgical specialisations use ionising radiation intraoperatively,10 the structural design of the operating theatre is a key element and an ideal opportunity for providing passive radiation protection measures built into the very architecture of the room.11 The layout of the radiation protection elements in the operating theatre is a topic that has seldom been studied in the literature, yet is very important.2,12–14 The operating theatre assigned to our department features an O-arm (Medtronic, Fridley, Minnesota, United States), a 3-dimensional imaging

system which combines tomography definition and navigator precision. With a view to structural remodelling, the design, spatial layout and shielding of the operating theatre were modified, and useful, novel radiation protection features were added. This study reports the various radiation protection measures available in our operating theatre, with a collapsible shielding screen being a key element. We provide dosimetric confirmation of said measures, discuss the advantages and disadvantages of the spatial layout of the operating theatre in relation to versatility and protection against radiation, and propose a number of solutions with implications for the design of multi-purpose neurosurgery operating theatres.

Material and methods The acquisition and use of an O-arm navigated 3D imaging device was the motivation behind a structural remodelling of the neurosurgery operating theatre, including a number of radiation protection measures. The details of the remodelling are shown in the sketches in Figs. 1 and 2, which provide specific information about the architecture, dimensions and shielding of the remodelled operating theatre. Placing a collapsible shielding screen on one end of the operating theatre represented a structural novelty with significant repercussions for day-to-day clinical practice. Fig. 3 shows its location and measurements as well as the positioning of the elements, equipment and staff of the operating theatre under normal conditions.

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EXTERIOR

Equipment storage

Pre-anaesthesia area Clean corridor Neurosurgery Operating Theatre

Theatre

Theatre

Dirty corridor

Soiled disposal

Hand-washing

Storage

EXTERIOR

Theatre Inner space

Theatre

Theatre

Storage

EXTERIOR Fig. 1 – Sketch of the architectural arrangement of the neurosurgery operating theatre. The operating theatre is at one end of one of the surgical blocks. Following the remodelling, its surface area was twice that of any other operating theatre.

Physical units of measure used In medicine, the damage done to the human body by any sort of radiation received is quantified with a magnitude called a radiation dose. The radiation dose absorbed by the human body is measured in International System (SI) units called greys (1 Gy = 1 J/kg and is equivalent to 100 rad under the British system). However, the actual biological effect of radiation depends in part on the type of radiation received, its energy and the specific sensitivity of the different organs and tissues of the body. This biological effect of radiation is quantified in terms of a magnitude called equivalent or effective radiation and measured in sieverts (1 SV is equivalent to 100 rem under the British system). For X-rays, gamma rays and electrons, 1 Gy is equivalent to 1 Sv. However, for alpha particles and free neutrons (which are much more harmful), a correction coefficient which may be as high as 20 must be used. The equivalent dose may be considered a measurement of the average dose that the body tissues received modulated by the risk to which each tissue is exposed. The dose of background radiation that a person receives depends on his or her geographic location of residence. Natural background radiation (around 1–3 mSv per year) essentially comes from natural radioactive materials from the ground and cosmic rays from outer space. Altitude, exposure to

radon gas (a product of natural decay of uranium present in soils and rocks), diet and other factors also play a role. For example, a chest X-ray is equivalent to natural exposure for approximately 10 days. Due to its biological effects, ionising radiation does not cause detectable symptoms below 0.1 Sv, although it does cause death at levels of 4–10 Sv in a single exposure.

Measuring devices used Measurements of radiation exposure were taken during the use of the C-arm and the O-arm at different distances from the radiation source and behind the screen. These measurements were checked using a Ludlum 9 DP pressurised ionisation chamber for detecting environmental radiation (Sweetwater, Texas, United States), supplied by RTI Electronics (serial number 25013445) and having been calibrated 2 months before measurements were taken. The personal and environmental dosimeters used were LiF:Mg:Ti thermoluminescence dosimeters (ThermoScientific brand, Harshaw model). They were used to measure doses of deep radiation (10 cm equivalent depth in water) and superficial radiation (0.07 cm depth) and read by the National Dosimetry Centre with compensation for local background radiation.

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5,405

Outer facade

Storage and work area 1-mm thick lead lining

Screen 2,000 1.5 mm thick lead lining

Framing for ceiling and floor: 30 cm thick concrete slabs

11,991

Surgery area 70.17 m2 Inner facade

8,150

Outer facade Control of laminar flow in ceiling

Door for stretchers (can be blocked from inside)

Operating table Door for staff

2 mm thick lead lining

Radiation use warning light

6,309 Inner facade

Fig. 2 – Sketch of the radiation protection elements of the operating theatre following the remodelling: shielding and positioning of the screen. The shielding of the walls is double on surfaces bordering inner corridors through which staff circulate. The doors and their windows are leaded. The shielding screen rotates easily on a wheel and may be unfolded to protect staff or folded up against the wall when not in use. The operating area (operating table, respirator, control of air and laminar flow) is relatively far from the equipment storage and radiation protection area thanks to the dimensions and rectangular shape of the room.

Results Description of layout of operating theatre Prior to the remodelling, the neurosurgery operating theatre was rectangular in shape with a surface area of 8.24 m × 6.31 m (52 m2 ) and a 1 mm thick lead lining on all the surfaces of the operation theatre, except for the outer facade and the windows in the doors. The structure of the framing for the ground and ceiling was made with 30 cm thick solid concrete slabs. Normal mobilisation of the O-arm (measurements: 67 cm × 265 cm × 192–222 cm) represented an exercise in a certain precision not without a risk of collision with other devices and contamination of the sterile area, due to the limited dimensions of the operating theatre.

The remodelling was to include adding an adjoined room, previously a storage area, to the surface area of the operating theatre and reinforcing the lead lining for the walls: 1 mm thick on outer walls and 2 mm thick on inner walls. The room’s shape and surface area changed considerably as the room became nearly rectangular and measured around 12.00 m long, 4.10 m wide at its narrowest width and 6.31 m wide at its widest width (Figs. 2 and 3). The total surface area ®

is now 70.17 m2 . The operating table (Maquet with a radiotransparent table top measuring 60 cm × 240 cm) is at one end of the room, closer to the entry doors and beside the respirator. The screen and radiodiagnostic devices are at the other end of the room and are also stored there when not in use (Figs. 3 and 4). The extra space gained, around 15–16 m2 , is used as an area to park the O-arm and store expendable items (sutures, haemostats, gloves, implants, etc.), a work

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Table

5,405

O-arm

Screen 2,000 Micro Nav

11,991

70.17 m2

8,150

Displays

O-arm NE

Table

SN

NE

SN

NE

Operating table

Resp AT Motor, bipolar, aspirator, etc.

Radiation use warning light

Storage

6,309

Fig. 3 – Diagram of the spatial layout of the elements of the operating theatre under normal use conditions following the remodelling of the operating theatre. The operating table, respirator, instrument table and various devices for use in surgery are at one end of the room, near the access doors. The door for stretchers may be blocked from inside throughout the procedure. Over the staff door is a pilot light that warns when radiation is being used. The area added to the operating theatre, at the other end of the room, enables parking of the O-arm and storage of expendable items; delimits a work area with a table, computer and telephone; and creates a radiation protection space for all staff when the screen is unfolded. When the screen is folded up against the wall, there is a large area for circulation of bulky elements such as the O-arm, microscope, navigator, workstation and endoscopy tower. AT: anaesthetist; SN: surgeon; NE: nurse; NT: neurophysiologist.

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The people managing the C-arm and the O-arm (physicians and nurses only) previously obtained the title of Accreditation to Operate X-ray Facilities for General Diagnosis, certified by the Spanish Nuclear Safety Council.

Exposure data

Fig. 4 – Picture of the back of the operating theatre where the O-arm is stored when not in use. This area provides a work area (left), a storage area for expendable items (right) and, with the screen folded up against the wall, a large space for circulation with equipment.

area with an Internet-connected computer and a phone, and a radiation protection area for personnel when the screen is unfolded. The most important structural novelty in terms of radiation protection was the installation of a collapsible lead screen (Fig. 5), connected with hinges to one wall and able to rotate 90◦ on a wheel, such that, when not in use, it can be folded up completely against the wall. The screen’s measurements (200 cm × 205 cm × 4 cm thick with a 1.5 mm thick lead lining) enable it to shelter and protect all operating theatre staff (at least 6–8 people) when radiation is in use. The patient, respirator and operation of radiology equipment may be managed through the leaded screen window (148 cm × 48 cm, 26 cm from the sides and 28 cm from the upper edge). In addition, a red pilot light was installed outside the operating theatre, just above the staff access door. This light warns of radiation use and may be activated or deactivated from inside. It is also possible to block the access door for stretchers from inside to prevent inadvertent intrusion into the operating theatre while any radiation-emitting device is in use.

While intra-operative data were collected with the O-arm for an adult patient with a standard body size (O-arm in large modality) in high-resolution mode for a procedure centred on the lumbosacral junction, radiation measurements were obtained using an environmental radiation detector. By way of example, a distance of 2.5 m from the centre of the gantry of the O-arm and a height of 1.20 m yielded a peak dose rate of around 0.8 mSv/h (radiation time during imaging is around 25–30 s per examination) and a cumulative dose for the entire examination of 4.9 ␮Sv. However, measurements taken from behind the screen window had a peak rate of 6.8 ␮Sv/h and a cumulative dose of 0.0 ␮Sv. This means that the screen provides radiation protection at least 2 orders of magnitude higher than no screen. Table 1 provides the dose and effective dose rates received in front of the screen at different distances (with or without an apron) and behind the screen (Fig. 6), with the O-arm or with the C-arm. The measurements without a lead apron reflect the doses to the parts of the body not covered by lead garments (arms, legs and head). Using activity data for our department (around 200 examinations with an O-arm annually), the effective dose received by staff one metre from the device with no protection (63.5 mSv) would be triple the annual allowed dose. Even if lead garments are worn, the dose to the parts of the body exposed at that distance is high—to which is added the dose to the rest of the body (around 3.8 extra mSv)—and represents a serious problem for the lens of the eye, for which the annual dose threshold is 20 mSv. In fact, the total effective dose (11.28 mSv/year) would require operating theatre staff to be classified as staff exposed to Category A radiation and undergo annual medical follow-up by an Occupational Risk Prevention Department. Doses received at a distance of 2 m with an apron (1.7 mSv) exceed the maximum allowed dose for the public (1 mSv annually), meaning that operating theatre staff must be classified as professionally exposed. If lead garments are worn, the doses to the limbs and the lens at

Fig. 5 – Picture of the functioning of the shielding screen. (A) Folding the screen up against the wall frees up the entire space for circulation of materials and staff. (B) The screen rotates easily on a wheel thanks to hinges and delimits a space where all staff are protected during radiation. (C) The anaesthesia monitor and radiology devices may be managed from behind the screen through its leaded window.

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Table 1 – Dose and effective dose rates received in front of the screen at different distances (with or without an apron) and behind it, with the O-arm or with the C-arm. 3D examinations with O-arm (Sv/h) Dose rate at 1 m without apron Dose rate at 1 m with apron Dose rate at 2 m without apron Dose rate at 2 m with apron Dose rate behind screen

33,400 4000 1290 909.9 32.9

2D examinations with C-arma (Sv/h) Dose rate at 1 m without apron Dose rate at 1 m with apron Dose rate at 2 m without apron Dose rate at 1 m without apron Dose rate behind screen

23,300 2500 5800 633 8.4

Dose in 3D examination with O-arm to operating theatre staffb (mSv/year) Operating theatre staff dose at 1 m without apron Operating theatre staff dose at 1 m with apron Operating theatre staff dose at 2 m without apron Operating theatre staff dose at 2 m with apron Operating theatre staff dose behind screen a

b

63.56 7.48 4.70 1.73 0.06

The C-arm is used in short bursts (2–3 s) to locate or confirm the level of the spine be treated. In a one-year period, 550 bursts were performed. Due to the limited exposure time and dose rate, the annual effective doses are minimal. Data for a one-year period in which 190 examinations with an O-arm were performed with a radiation time of 26–30 s per examination.

this distance (5.8 mSv) are still high, although not in excess of the thresholds established for professionally exposed staff. Behind the screen, the annual cumulative dose is infinitesimal (0.06 mSv) and falls below the detectable threshold of conventional dosimeters. More than 1000 imaging procedures were performed with the O-arm from June 2012 to June 2017. The monthly cumulative radiation received by department staff throughout this period, measured with a personal dosimeter, consistently fell below the detectable level (0.1 mSv) for all staff members. In addition, an area dosimeter was placed to monitor the total cumulative dose behind the collapsible screen for a 12-month period from November 2013 to October 2014. The reading for this dosimeter also fell below the detectable threshold. In addition, the radiation doses in the corridors adjoining the operating theatre could not be detected during the use of the C-arm or the O-arm.

Discussion Effects of exposure to ionising radiation It is known that ionising radiation may cause direct or indirect damage to cell DNA, generate free radicals or even induce neoplastic differentiation and proliferation.8,15,16 The biological effects of ionising radiation may belong to one of 2 types: deterministic or stochastic. Deterministic effects occur when a certain threshold for exposure is reached. In general, their seriousness is dose-dependent (mucositis, hair loss, cataracts, etc.), and they may be prevented by monitoring exposure levels. By contrast, stochastic effects, whose incidence increases with exposure, appear without any identified threshold or minimum time and are generally linked to carcinogenesis and teratogenesis.2,17

Fig. 6 – Pictures of the measurement assembly. (A) Measurement in front of the screen at a distance of 1 m with mannequin representative of the body (40 cm in diameter). (B) Measurement at a distance of 1 m with a lead apron and mannequin representative of the head (20 cm in diameter). (C) Measurement behind the collapsible shielding screen.

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The radiation received by the staff may be direct or scattered. Direct radiation is received from the radiation source and essentially affects exposed patients, surgeons and nurses. Scattered radiation occurs on a secondary basis when the ray from the source crosses the patient and is partially reflected and scattered in all directions, thereby also affecting the surrounding staff who are farthest away. According to the guidelines of the International Commission on Radiological Protection (in Spain regulated through Royal Decree 783/2001, of 6 July, approving the Regulation on healthcare protection against ionising radiation), the Sievert is used as a unit of exposure as well as a direct measurement of the deterministic effects and an indirect measurement of the stochastic effects of ionising radiation, such that exposure to 1 Sv corresponds to a 5.5% increase in the risk of developing a neoplasm.17 According to these guidelines, the general public should not receive more than 1 mSv per year over the course of 5 years, while professionals who work with radiation may receive a cumulative dose of up to 100 mSv over the course of 5 years, provided that they receive no more than 50 mSv in a single year. Staff in training should receive no more than 6 mSv per year, and pregnant women should receive no more than 1 mSv throughout the pregnancy. The annual doses to the lens and skin/limbs for non-exposed staff and the public are 15 mSv (this will be reduced to 2 mSv in the future transposition of Directive 2013/59/Euratom) and 50 mSv, respectively. These maximum allowed doses are multiplied by 10 for exposed staff. By way of illustration, 1 ␮Sv is approximately a tenth of the dose that a person travelling by aeroplane between Spain and the United Kingdom would receive, or a fifth of the mean annual dose received by anybody due to radioactive fallout. Moreover, 1 mSv is the dose that a person who lived in an area of the Himalayas at an altitude of 6700 m for 42 days would receive. This is somewhat more than 40% of the average annual dose that a person in Spain receives due to natural background radiation. According to data from the Spanish Nuclear Safety Council,18 the mean radiation dose for the Spanish population is 3.7 mSv per year. Of this, 2.4 mSv come from natural sources and the remaining 1.28 mSv are due to diagnostic tests (1.2 mSv due to X-ray diagnostic techniques and 0.08 mSv due to nuclear medicine tests). Nuclear plants, hospitals and research centres emit radiation into the environment in the ␮Sv range. Radiation from nuclear tests has decreased since the 1970s (0.08–0.14 mSv) to very low levels at present (5–10 ␮Sv). Radiation received from everyday objects such as smoke detectors, luminous watches, certain consumer appliances and aeroplane travel is in the range of 10 ␮Sv, although it may accumulate up to one mSv. In Spain, the dose that may be attributed to radon-222 (from natural uranium in rocks) is 1.15 mSv per year and may be up to 40 mSv in certain regions. In Spain, around 85,000 people are professionally exposed and treated through radiological monitoring. They receive 0.83 mSv on average (nuclear plant workers receive 1–2 mSv on average). Most (98.65%) receive less than 5 mSv per year; this is a quarter of the maximum allowed. According to 2017 data from the Radiological Society of North America,19 the effective radiation doses associated with

various radiation diagnostic tests are as follows: Limb X-ray and densitometry, 0.001 mSv; chest X-ray, 0.1 mSv; mammogram, 0.4 mSv; spine X-ray, 1.5 mSv; head CT scan, 2 mSv; spine CT scan, 6 mSv; chest CT scan, 7 mSv; abdominal and pelvic CT scan, 10 mSv, and PET/CT scan, 25 mSv. Radiation received due to fluoroscopy depends on various factors such as patient size, amount of kilovoltage used and mode of magnification employed. For example, for devices that emit a dose rate of 30 mGy/min, 5 min of radioscopy would be equivalent to a dose of 150 mGy absorbed through the skin. The use of an O-arm in spinal surgery is equivalent to 1–2 mSv per examination, depending on the physical characteristics of the patient, the spinal segment that undergoes radiation and the mode of definition used in the machine. According to a study by Nottmeier et al.,20 each rotation of the O-arm in high-definition mode corresponds to an exposure of 1.77 mSv measurable in detectors placed in the gantry itself, but only 7–36 ␮Sv in detectors at a distance of 3–4 m.

Radiation protection measures in the neurosurgery operating theatre The “as low as reasonably achievable” (ALARA) principle is a basic standard in radiation protection. It means going beyond efforts to keep doses within acceptable limits, making sure they are as small as possible. Dose reduction is achieved through 3 factors: shielding, distance and time.8 The dose received decreases when the shielding that intercepts radiation is greater, the distance from the radiation source is greater, and the duration of exposure is less. Shielding refers to physical barriers (generally made of lead or high-density plastic) that absorb part of the radiation so that it does not leave the operating theatre (shielding of walls, floors and ceilings); clothing that protects staff such as aprons, thyroid protectors, goggles and lead gloves; and partitions or screens positioned such that the radiation source and the surgeon are on one side and the rest of the staff are on the other side. These lead garments significantly reduce radiation exposure, by up to 96%,21,22 but have disadvantages such as weight, restricted mobility and lack of complete coverage of the body. The distance to the radiation source is a key factor, given that the exposure received decreases as the square of the distance decreases. Therefore, this distance must be maximised to the extent possible. Scattered radiation decreases to less than 0.1% of the original amount from a distance of approximately one metre or more, according to various studies.23,24 When the C-arm is used, the position of the surgeon in relation to the radiation source is also important. It is recommended that the radiation source be opposite the surgeon in an effort to increase the distance between the centre of radiation and the staff.8,25 Scattered radiation has a lesser effect on surgeons who position themselves beside the image intensifier.26 Exposure time may be minimised by making rational use of radioscopy (at the discretion of the surgeon) and using different radiation emission modalities: low-dose (by using certain technologies27 or decreasing kilovoltage) or pulsed

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(intermittent radiation emission; 1–6 image[s] rather than 30 images).8 Combining the two modalities may significantly reduce exposure by up to 50%.28 Pulsed radiation seems to be especially beneficial in procedures in which the surgeon must be very close to the patient while radioscopy is under way.28 These methods, along with physical barriers, may reduce exposure in spinal surgery by up to 97%.29 Other potential sources of assistance are beam collimation (restriction of the radiation field to the anatomical site of interest), intermittent fluoroscopy and the use of the last image hold method.22 ® Radioabsorbent surgical drapes (such as RADPAD , WIT Inc., Kansas City, United States) block up to 95% of scattered radiation in interventionist radiology procedures, vascular surgery, catheterisations and percutaneous procedures.30,31 They protect both patients and staff, and their efficacy depends on the anatomical site where they are positioned, although they are not superior to the protection provided by a lead apron.32 They do not contain lead, are disposable and can be used to make very light garments such as surgical caps and thyroid protectors. Although the initial objective of 3D imaging systems with integrated navigation was to increase precision in placing spinal instrumentation, as a secondary matter, a significant reduction in exposure to radiation on the part of the operating theatre staff has been reported.33,34 This is because images for use in navigation may be obtained

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before or during the procedure, with no need for the staff to remain inside the operating theatre while the test is being performed. This applies to both the isocentric C-arm (which covers 190◦ ) and the O-arm (which covers 360◦ ). However, the radiation that the patient receives seems to be greater (by a factor of 2–3), both in C-arm systems and in O-arm systems, compared to classical radioscopy.26 According to a recent study,35 patients treated by means of posterior pedicle fixation with an O-arm received over 8 times more radiation than operating theatre staff and 2.77 times more radiation than is received in surgical procedures without navigation, taking into consideration that the mean total exposure of patients was 5.69 mSv. This figure is comparatively lower than the 7.5 mSv received in a routine lumbar CT scan. Systems that use intra-operative resonance do not produce any ionising radiation and are used to locate the anatomical level of interest or to confirm the degree of decompression of neural tissue, but are not useful for placing instrumentation materials. Moreover, it is necessary to perform regular checks of the functioning of radiation-emitting radiodiagnostic equipment and ensure that device calibrations and tune-ups comply with current regulations (Royal Decree 1085/2009, of 3 July, approving the Regulation on installation and use of X-ray devices for purposes of medical diagnosis, Spanish Official State Gazette [BOE], Saturday 18 July 2009, and Royal Decree 1976/1999, of 23 December, establishing radiodiagnostic quality criteria). It is

Fig. 7 – (A) Picture from the back of the operating theatre during a procedure using the O-arm. (B) When the screen is unfolded, the staff may protect themselves behind it and manage patient imaging and monitoring through the window while activating the system remotely using a pedal. (C) While imaging with the O-arm is underway, the staff move behind the screen. (D) Once the CT scan has been performed, the procedure continues. Note the large amount of equipment present during the procedure. Hence the advisability of having a large enough surface area to locate, circulate and store all devices.

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also necessary to perform readings of personal and environmental dosimeters as well as measurements of exposure of rooms based on degree of exposure. A so-called hybrid room (a cross between an interventionist radiology room and an operating theatre) combines suitable technological equipment from a radiology perspective and an aseptic environment close to that of a conventional operating theatre.11,36 In general, these facilities are intended for performing invasive radiological tests such as catheterisations, percutaneous drains, endovascular studies and treatments and percutaneous biopsies among others. However, they are not versatile enough to be used as a neurosurgery operating theatre, except for minor surgeries. Finally, exposure received when the C-arm is used in minimally invasive spinal surgery during the phase in which the lesioned level is located should not be underestimated, as it may account for up to 50% of the entire dose absorbed in procedures performed on the thoracolumbar area.37

Advantages and disadvantages of our operating theatre layout In our opinion, the 2 main advantages of the layout reported are as follows: - The screen fully protects all operating theatre staff against radiation, and only the patient receives radiation (Fig. 7). A balance must be struck between, on the one hand, the risk of patient radiation and, on the other hand, the precision provided by the O-arm and the fact that some staff, especially scrub nurses, neuroanaesthetists and neurophysiologists, who work in the operating theatre on a daily basis, cease to be exposed to any radiation at all, including parts of the body not protected by aprons. The ease of performing an intra-operative monitoring CT scan comes at a cost of an increase in patient radiation. However, it does not require a subsequent monitoring CT scan as a matter of course; such a study entails exposure to somewhat more radiation than the O-arm. In a typical spinal fixation surgery, the dose received due to the study needed to place the instrumentation and the subsequent monitoring study (both intra-operative and totalling 2–3 mSv) is an exposure dose that can be assumed. - It decreases the risk of contamination and improves the management of asepsis, given that it is not necessary to leave the operating theatre or to open the doors at virtually any point during surgery, these being actions with consequences for maintaining asepsis, positive air pressure and laminar flow. In addition, when operating theatre staff are trained and accredited, auxiliary staff (porters, radiology technicians, etc.) are not needed to manage the O-arm. This minimises the number of people in the operating theatre and also promotes asepsis. The large surface area and rectangular shape enable fluid circulation of materials and equipment with no collisions, which decreases the potential for contamination of the sterile area.

However, this layout leaves 2 questions unanswered. The first is how the surgeon will be protected in specifically percutaneous procedures (for example, in placing electrodes with radioscopy), when the surgeon must remain with the patient during radioscopy. The second is how to solve the problem of patient over-radiation, which does not mean that certain measures such as placing lead aprons over areas adjacent to the anatomical site of interest and radioabsorbent drapes cannot be used. Table 2 lists the advantages and disadvantages of the proposed layout.

Implications for the design of multi-purpose neurosurgery operating rooms In our opinion, the 3 most important considerations to be taken into consideration when designing a new multi-purpose neurosurgery operating theatre in which radiodiagnostic equipment is to be used are as follows: - In our opinion, the shape of the operating theatre is ideally rectangular (as opposed to square) in order to maximise the distance from the radiation source and to have an area at one end of the room where radiodiagnostic equipment can be stored with no need to bring it in from outside each time it is used. This factor is, of course, subject to the characteristics of the building which houses the operating theatre. - The total surface area of the operating theatre should be as large as possible (>50 m2 ) as this facilitates equipment circulation and mobility and minimises the potential for collisions between objects or contamination of sterile materials. The current trend is to use more and more equipment, often simultaneously (microscope, navigator, neurophysiology equipment, ultrasonic aspirator, endoscopy, etc.); this equipment occupies a great deal of space around the operating table (Fig. 7). - The screen should delimit a radiation protection area inside the operating theatre large enough so that all staff are protected behind it and nobody has to leave while examinations are underway. The cord for the pedal or remote control to activate both the C-arm and the O-arm (4.5 m in our case) should be long enough to operate the device without emerging from behind the screen. Other authors have successfully used similar screens in the operating theatre in percutaneous vertebroplasty treatments with a remote injection device. In a study by Zhang et al.,38 when the surgeon was protected behind a lead screen at a distance of 4 m, the average dose received was 0.10 ␮Sv versus 12.1 ␮Sv — i.e. 2 orders of magnitude lower, as in our study. In our opinion, a lead screen confers virtually complete radiation protection as well as asepsis and climate control, as it minimises circulation of staff, given that nobody needs to leave the operating theatre during examinations, and that nobody needs to enter either. This is assuming that the people who manage the devices possess the applicable accreditation. Following 5 and a half years of experience we discovered a structural problem with respect to the intra-operative use of the O-arm associated with the strength of the floor on

Table 2 – Advantages and disadvantages of the proposed layout of the neurosurgery operating theatre from a radiation protection perspective. Operating theatre: lead-lined walls (1–2 mm thick), floors and ceilings with concrete slabs (30 cm), storage of typical expendable items for anaesthesia and surgery inside the operating theatre to prevent opening doors unnecessarily. Laminar flow and management of pressure and temperature. Radiological imaging systems built into walls. Computer resources and telephone inside the operating theatre. Option to block doors from inside to prevent access during radiation. Operating theatre size: The rectangular shape enables a greater distance to be maintained from the radiation source along the longer axis of the room. The total length (>11 m) and surface area (>70 m2 ) provide enough distance and space to use and store the O-arm. Each professional has space to work without disturbing anybody else. Screen: The collapsible lead screen, placed at the back of the room, enables equipment and staff to move around unimpeded and provides full protection for all staff, with no need to leave the operating theatre (risk of contamination). It blocks >99% of radiation. Nobody needs to wear a personal dosimeter due to this exposure. Nobody needs to wear lead aprons or other protective gear. Staff members’ entire bodies are protected, not just the parts covered by the apron. Staff: The O-arm is managed by operating theatre staff (physicians and nurses) trained in its use by the Spanish Nuclear Safety Council for the use of radiodiagnostic devices. This means that cooperation with radiology techniques is not required. Nobody enters or leaves the operating theatre as long as imaging is under way. A warning light outside the operating theatre indicates when radiation is in use. ASEPSIS: an aseptic environment is ensured, as it is not necessary to open the doors of the operating theatre at any time during the procedure (neither laminar flow nor positive air pressure is affected), given that there is no need for cooperation with porters or radiology technicians and scrubbed staff need not leave the room. The number of people in the operating theatre (surgeons, anaesthetist, scrub nurse, circulating nurse and neurophysiologist) is minimised. O-arm: ease of management, lack of need for technical assistance, minimal learning curve, ease of covering the sterile field with protective plastic and lack of need for expendable items.

Disadvantages

It does not solve the problem of radiation to the surgeon and scrub nurse in surgical procedures which require continuous radioscopy close to the patient (for example in placing spinal electrodes). The larger the operating theatre, the more difficult it is to maintain climate control and asepsis. It does not solve the problem of patient over-radiation. There is the option to protect all parts of the body apart from the anatomical site of interest. The C-arm (which, in our case, is shared with other operating theatres) cannot be stored in addition to the O-arm. It requires experienced, accredited staff. It does not solve the problem of large numbers of cords on the floor. It requires placing the respirator at the patient’s feet, which sometimes complicates anaesthesia. It requires a longer length for expendable items for anaesthesia (lines, tubing, etc.).

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Advantages

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Table 3 – Implications of various important matters for radiation protection in the design of multi-purpose neurosurgery operating theatres. Theatre

Lead lining for walls Screen

Floors and ceilings

Safety

Doors Modularity

Preferably rectangular versus square: facilitates mobility and storage of equipment and moves the radiation source as far as possible Recommended length: 10–12 m Recommended width: 6–7 m Recommended surface area: at least 60–70 m2 Minimum thickness: 1 mm on outer walls; 2 mm on walls adjoining hallways and inner rooms, through which staff circulate Height of 2.05 m, width of 2.00 m and thickness of 4 cm, shielding of 1.5 mm of lead, distance from the radiation source of at least 3–4 m; personal and environmental dosimeters unnecessary Recommended thickness of framing for ceiling and floor of at least 30 cm; lead lining not required Suitable floor surface strength to move the O-arm around (weight >800 kg as it rests on wheels) Blocking of doors from inside to prevent unexpected intrusion from outside during radiation Outside radiation warning light, preferably automatically activated Leaded, size needed to bring in and take out radiodiagnostic equipment (C-arm: 230 cm; O-arm: 265 cm in length) as needed It is preferable that radiodiagnostic devices and all other equipment (such as the respirator) be separate modules (easier to transport, change, take out of the operating theatre and repair) as opposed to modules built into the structure of walls and ceilings, which limit the potential for movement

which the device moves around. Due to its weight (>800 kg) and repeated use, the surface of the floor became deformed. This made it nearly impossible to move the O-arm around. The surface of the floor should be very smooth and should not deform under weight. In our case, the floor needed repair after just 4 years of use, as wrinkles gradually formed in the waterproof plastic covering for the flooring (levelling paste) such that the device had to be pushed hard and attempts to move it around caused it to jump. Table 3 summarises a number of suggestions that, in our experience, may be useful in terms of radiation protection in the design of multi-purpose neurosurgery operating theatres. The design and construction of a neurosurgery operating theatre featuring radiation protection measures such as those reported come at a higher cost than conventional operating theatres. However, the upgrades made in this regard when building the room are available for the entire useful life of the operating theatre. Increasing the surface area, adjusting the shielding and installing screens and other radiation protection systems may be relatively easy and comparative inexpensive when the operating theatre is being built as opposed to when it is undergoing subsequent remodelling. Failure to take these matters into consideration in the design phase may have permanent, irreversible implications for the radiation protection of the operating theatre, especially in terms of measurements and surface area. From a functional perspective, it is tempting to build all the operating theatres at a centre with similar characteristics and dimensions towards rendering them multi-purpose. However, the neurosurgery operating theatre has some unique features and therefore is not readily interchangeable with an operating theatre for another surgical specialisation. The essential reasons for this are the large amount of equipment that may be

used during surgery, often simultaneously, and the need for bulky radiodiagnostic devices and cooperation with staff from other specialisations.

Conclusions The design of a neurosurgery operating theatre in which radiation-emitting devices are used must incorporate radiation protection elements. To minimise the radiation dose that the patient receives, surgeons and operating theatre staff must follow the standards of the ALARA principle, essentially with regard to shielding, distance from the radiation source and exposure time. The installation of a collapsible shielding partition in the operating theatre provides a radiation protection space for all staff present. This element eliminates the need for the use of personal dosimeters, lead aprons and other protective equipment and protects the entire body. In addition, the need to open and close the doors of the operating theatre is minimised, given that the equipment is stored inside and, when staff are trained and accredited, there is no need for cooperation with radiology technicians. The shielding of walls, ceilings and floors; the operating theatre having a rectangular shape and the largest possible surface area; the presence of a radiation protection screen; and safety systems that prevent unexpected entries into the operating theatre when radiation is in use are important matters to be taken into account in the design of a neurosurgery operating theatre. The design and construction phase of the operating theatre is the ideal time to implement these radiation protection measures.

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Conflict of interests None of the authors reports having any conflict of interest with respect to the content of this study.

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