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24 May 2012

Answer to Question #8187 Submitted to "Ask the Experts"

Category: Medical and Dental Equipment/Shielding — Shielding

The following question was answered by an expert in the appropriate field:

I would like to know which is the dominant practice in our days in a radiotherapy treatment room concerning the shielding doors. Should it be a swing door or a sliding one? What are the advantages and the disadvantages of each?

Typically, swing doors are used for radiotherapy treatment rooms with mazes. Rooms without mazes are normally shielded with a heavy direct-shielding door which provides the same attenuation as the adjacent secondary barriers of the room.

Swing doors are equipped with a motorized opener, and one must ensure that appropriate motors and hinges are used and that the hinges are hung correctly. The weight limitation for a swing door that is 120-cm wide lies in the range of 8,000 to 9,000 kg (NCRP 2005).

Sliding doors are used when the latter weight limits are exceeded. Sliding doors may either be hung from a rail or roll on a steel floor support. The doors are either electrically or hydraulically driven, and it is important that the patient can be reached in case of electrical failure. One option is to provide for an escape hatch in an adjacent barrier. For hydraulic doors, a back-up air drive that allows manual opening should be provided in case of electrical failure.

It is prudent to implement periodic inspection and routine preventive maintenance procedures since there have been accidents with the door closure systems and support structures. Since these doors are so heavy that they are capable of crushing someone in their path while closing, it is recommended that these doors be equipped with presence (or motion) and pressure sensors.

Both types of doors should be equipped with interlocks, kill switches, and emergency power or battery backup and should meet American National Standards Institute standard door opening and closing times. "Partial Open" is also a useful feature, as it allows the therapist to enter the room without waiting for the door to open fully. National Council on Radiation Protection and Measurements Report No. 151 provides useful information on the shielding design of such doors.

Nisy Elizabeth Ipe, PhD, CHP

Reference
National Council on Radiation Protection and Measurements. Structural shielding design and evaluation for megavoltage x- and gamma-ray radiotherapy facilities. Bethesda, MD: NCRP; NCRP Report No. 151; 2005.

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