Design Of Teletherapy Units

Radiation and Architectural Considerations for Cobalt-60 Unit

By the term teletherapy, we »re restricting ourselves to the use of radiation et a distança; thet is, the subject and source are separated by a distance of 50 centimeters or more. In particular, we era concerned with the usa of the radioactive isotopes cobalt*60 end cesium-137 as sources of radiation in teletherapy units-

We have restricted our discussion to ,uCo and "'Cs, primarily beceuse thay are the more familiar of the isotopes suggested for use in teletherapy units- We are not including the use of radium and high energy «-rays, since soma of the problems associated with ihese are quite different in their solution and nature.

The primary purposes of this article are to furnish architects who are anticipating a teletherapy unit with information on basic radiation protection ideas and techniques, and to serve as a guide In tha solutions of certain architectural problems- We are by no maans attempting to evaluate the advantages and dir advantages of "Co and ,3'Cs units against other types of units.

For a discussion of tha fundamentals of radiation shielding and a glossary of radiation terminology, see Architectural Record, November, 1957, pages 218-220.

In planning a cobalt installation, it should be understood that each type of machina and its location within the building will present a different problem which will require an individual solution. Consequently, no one type plan can be designed which will take cere of tha various shielding requirements presented by tha different machinas and installations. The archi* tact is dependent upon other professional for specific technical information he needs before ha can intelligently design a building containing a cobalt teletherapy unit. The problems incurred may materially affect the orientation, location, and structural and functional design of the building. Therefore, during preliminary design stages, close cooperation between architect, radiologist, and radiation physicist is nacassary to develop an efficient and economical layout,

It should ba noted that the Atomic Energy Commission places responsibility upon the applicant for conditions of installation and use of the facility. Since the use of a facility is largely dependent upon the conditions of installation, it is to tha applicant's advantage to secure the services of a radiation physicist at tha inception of s project. Hia function ia to advise the applicant and architect on radiation

Wilbur R Taylor is a Hospital Architect in the Division of Hospital and Medical Facilities. Bureau of Medical Service, Publrc Health Service, Department of Health. Education, and Welfare and William A Mills and Jamas G Tarrill, Jr are respectively Radiation Physicist and Chief of Radiological Health Program. Division of Sanitary Engineering Services. Bureau of State Services, Public Health Service requirements, assuma responsibility for tha final design as to shielding providad and furnish the supporting information required in Application Form AEC-313 relative to exposure rates in areas surrounding the teletherapy room and occupancy factors assigned,

Fundamental decisions as to: (1) the type of machine, {2) strength of the source, (3) desired location, and (4) tha shielding required for tloor, walla, and ceiling must be made before the building's structural syatam can be designed During tha early design, It may ba determined that tha structural system cannot support the weight of the shielding, or perhaps soil conditions will not permit sufficient excavation for a subgrade installation. It may then be necessary to change or altar one or mora of the following: tha machine or Its operation, the source strength or the location of tha room.

To those not familiar with such shielding problems, the included plans have been developed to illustrate tha shielding naceasary for three types of machines in specific locations. However, before considering the detailed plana, it may be deairable to discuss some of tha general requirements of auch facilities,

Location

The cobalt suite should adjoin tha x-ray therapy department. This location permits the joint use of waiting, dressing, toilet, examination, work and consultation rooms. In addition, it offers the important advantage of having tha staff concentrated in one area, thereby eliminating the conaiderable loss of lime involved in traveling to a remote location. This is an important consideration and justifies tha coat of any additional shielding that may ba necessary to achieve It.

A location below grade, unoccupied above and below, will require lass shielding. However, if such a location separates the cobalt and tha x-ray therapy departments, it may ba mora costly in both loss of staff time and efficiency than the coat of concrete shielding amortized over several yaara. If. for example, twenty-five minutes per day are loat in traveling to a remote tooetion, one additional patient could ba treated in this lime each day—or 240 patianta per year, Assuming a staff salary of $20,000 par year, this loas of twentyfive minutes per day results in an indirect salary loaa of SI032 per year, which would aoon equal tha coat of shielding in a new facility.

A corner location for tha cobalt room Is usually desirable since through traffic Is eliminated, only two interior wella require shielding, distance to tha property line utilises the inverse square law to reduce shielding and the structural requirements ars mora easily solved.

Teletherapy Room Details

Size The room size may vary to suit different manufacturers' equipment A room approximately 1 6 ft by 1 8 ft by 9 ft-6 In. plus the necessary entrance mate, will accommodate moat of tha machines commercially available with tha exception of tha largest rotating models. For reasona of cost, the room should be ss compact as possible after allowing space to install the equipment and to position tha treatment table.

Shieldinfl The shielding nacassary for a room must not only be considered in tarma of floor, ceiling and wall shielding, but slso such things ss doors, windows, ventilation and heeting ducts, and safety locka. Radiation thai might escape through such possibilities could result in overexposure to personnel. If proper precautions are not taken.

Entrance The primary purpose of specific antrance construction is to protact personnel. It should also provide sufficient space to admit a stretcher and the largest crated piece of equipment. In some caaaa, a considerable savings In cost of assembling equipment may ba had by making tha door and maze large enough to admit the crated aeasmblad machine. For thla purpose, aoms manufacturera specify a door opening of 4 by 7 ft and a minimum distance of 6 ft at tha end of the max«.

Rather than add large amounts of laed to doors, tha shielding problem may be solved to soma degree by having the door to the teletherapy room open into a maze. This maze should ba built eo that no primary radiation could fall directly on the door. In designing doors for such a room, s good practice ia to have a door of wood with a layer of lead. This lead can either ba on tha inside surface, or between layers of wood. Commercially available x-ray doors aerva well for this purpose. The spsce between the door and floor can usually ba ahteldad by using a lead strip under tha door or by making a alight riea in tha floor containing lead, on tha outer side of the door-Lead shielding at tha jamb and head between the frame and buck may be eliminated by the use of a combination frame snd buck sal in concrete.

For safety precautions, tha door look should ba such that the door can ba raadily opened from inside tha cobalt room.

Coiltiol View Window It is Standard practice to locate thia window at a height which will permit the operator to be seated during tha treatment period, 4 ft-O in. from tha floor to tha center of tha window being an optimum distance. In plan, the window should be located in the area of minimum radiation and tor convanianl observation of the patient. This position, for a rotational machine, would be along the axis of rotation, and for a fixed beam unit, 90° to the plana of tilt.

From the control view window tha entire room should be in full view, using mirrors whan nacassary, Tha glass should contain lead or other materials in amounts which would provide shielding equivalent to tha surrounding concrete. Tha frame ia ueually packed with lead wool and should ba designed to offset tha shielding loss of tha reduced concrete thickneaa at beveled areas. Tha cost of such special glass and frame Increases rapidly with siza and an 8 by 8 in. window Is considered an optimum size.

H Siting and All Conditioning Tha only problem in relation to heating and air conditioning not encountered in other buildings is that of providing shielding where walls are pierced with supply and return duets. The usual solution is to locate ducts and openings in walla which are least subject to radiation and offset the path of duota through the well, lead or other high density material being added, where necessary, to maintain the shielding value of tha wall displaced by ducts.

Electrical Electrical service required for tha machine will vary with each manufacturer's equipment. Voltage will vary from 110-single phase to 220-thraa phase for large machines.

Room lighting should aasure good over-all illumination, preferably from cove lighting or an indirect type of fixture. M is essential

STUftT SIDE

(^'j F"" Occupancy Controlled

Pit t'\ Ich ftv ft For Design Requirements wo nfixl pogn.

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