KMCT DENTAL COLLEGEManassery, Mukkam

DESIGNING THE RADIOGRAPHIC

DARK ROOM

Presented By:Niyas Ummer

PG StudentDepartment of Oral Medicine and Radiology

Introduction

The x-ray exposure to produce a radiograph of satisfactory diagnostic quality, with minimum exposure to the patient, depends on:

Exposure technique Film-screen combination Proper handling of the film Processing of the film

These require a good darkroom and proper developing techniques.

Overview

1. Designing the Radiographic Room Controlled areas Location Layout Room Size Shielding Ventilation Control Panel Warning lights

2. Designing the Dark Room Minimum Requirements Layout Light-tight Processing Room Darkroom Entrance Safelighting Processing Tanks Processing solution temperature Ventilation Storage Place Viewing Area

Regulatory Acts

a) Section 17 of the Atomic Energy Act, 1962, and the Radiation Protection Rules (RPR), G.S.R. - 1601, 1971 issued under the Act – Radiation safety in handling of radiation generating plants

b) Radiation Surveillance Procedures for Medical Applications of Radiation, G.S.R. - 388, 1989, issued under rule 15 – General requirements for ensuring radiation protection in installation and handling of X-ray equipment

Designing the Radiographic Room

Concept of ‘Controlled area’

It is important to designate a ‘controlled area’ around the dental x-ray equipment, to help ensure that the measures provided under regulations are effective in preventing or restricting routine and potential exposures. Prohibiting normal access to the controlled area during radiography is a must. A controlled area will only exist whilst x-rays are being generated.

Controlled area is considered to be: within the primary x-ray beam until it has been sufficiently attenuated by distance or

shielding within 1.5 m of the x-ray tube and the patient, in any other direction

Since the beam is not fully attenuated by the patient, the controlled area is considered as extending beyond the patient until intercepted by primary protective shielding.

Location of X-Ray Installation

It should be located as far away as feasible from areas of high occupancy and general traffic.

If located in a residential complex: Wall on which primary X-ray beam falls should not be not less than 35 cm thick brick

or equivalent Wall on which scattered X-ray fall is not less than 23 cm thick brick or equivalent Shielding equivalent to at least 23 cm thick brick or 1.7 mm lead in front of the

door(s) and windows

Layout of Rooms

The number of doors for entry to the X-ray rooms shall be kept to the minimum. It shall not be possible to direct the primary X-ray beam towards dark room, door, windows, and control panel, or areas of high occupancy.

Room Size

Total area of the radiography room shall be not less than 18 m2. There should be a minimum area of 150 sq. feet. No single dimension shall be less than 4 m. Not more than one unit of any type shall be installed in the same room.

Orthopantomography (OPG) units:Room size shall not be less that 15 m2. No single dimension shall be less than 3.5 m.

Shielding

An appropriate structural shielding for walls, doors, ceiling and floor is mandatory. In addition, appropriate shielding for the dark room is also necessary (ensure that the undeveloped X-ray films are not exposed to more than 10 mGy per week).

Brick or concrete are the best materials for shielding as they are easily available, economical, and have good structural strength. Lead cannot be used, as it is a weak structural material with tendency to lose uniformity, needs periodic radiation survey to ensure its continued adequacy, and poses a serious environmental hazard and the use of it is being discouraged the world over.

Openings and Ventilation

Unshielded openings for ventilation or natural light, must be located above a height of 2 m from the finished floor level outside the X-ray room.

Control Panel

For equipment operating at 125 kVp or above:Control panel must be installed in a separate room located outside but contiguous to

the X-ray room, along with appropriate shielding, direct viewing and communication facilities.

For machines upto 125 kVp:Control panel should be located in the X-ray room. The distance between control

panel and X-ray unit stand shall be not less than 3 m.

Waiting Areas and Warning Light

Patient waiting areas shall be provided outside the X-ray room. Suitable warning signal (red light) at a conspicuous place outside and kept “ON” when the unit is in use. Appropriate warning placard should be posted outside.

Location of Dark Room

It should be located adjacent to the X-ray room such that no primary or secondary X-rays reach inside.

Designing the Dark Room

Minimum Requirements

i. Light-tight roomii. Both safe-light and white-light illumination

iii. Processing tanks and / automatic processoriv. Hot and cold running waterv. Accurate thermometer and interval timer

vi. Drying racks or dryervii. Adequate storage space

viii. A radiograph viewerix. Has a light-tight storage draw for unexposed extra-oral film

Layout

Room should be atleast 4 x 5 feet in size, such that it should be convenient to the x-ray machines and dental operatories. The room should be large enough to avoid crowded conditions. Equipment should be arranged to be within arm’s reach. The room should located as close as possible either to the X-ray clinic or the reading area.

Walls should be of a light pastel color (to reflect the room illumination). If humidity is a problem, air conditioning is a must.

Light-Tight Processing Room

Exclusion of all external white light is mandatory when radiographs are processed. This is possible by using a door that can be locked to avoid accidental exposure, a light outside the door (indicating that the darkroom is in use), a maze walk in (helpful for heavy traffic in and out), etc.

Safelight

Processing room must be provided with both:a. White light - cleaning tanks and preparing the solutionsb. Safelight - provide adequate light of quality that is “safe” for exposed X-ray films

during handling and processing

Fluorescent lights should not be used as overhead lights, because of their short afterglow that may fog the first few films opened after the light has been turned off. Always remember that X-ray films are sensitive to light until after fixation! Excessive exposure of the film to safelight illumination will result in fog.

Factors to consider: Type of filter Intensity of illumination Wattage of bulb Distance of safelight lamp above working area Time film is exposed to the safe light

a) Types of Filter: Amber or red filters should be used. Never use a ruby or red light bulb as it can cause fogging. To use least amount of light for the safelight lamp, Wratten series 6B or Morlite 2 (ML 2) filter is advised.

b) Intensity of Illumination, Wattage and Distance of Safelight: Intensity is controlled by wattage of the bulb and the distance of the safelight from the working surface. The recommended minimum distance is 120cms (4 feet) above the working surface. Intensity on the film varies with distance and also with the wattage of the bulb, hence, correct intensity can be obtained by adjusting either the distance or the bulb wattage or both. For D Speed film, a 15 W bulb should be used. For E Speed film, a 7 ½ W bulb is recommended.

c) Time the x-ray film is exposed to safelight: It must be made clear that there is no such thing as an absolutely safe safe-light. The film will be fogged if it is exposed too long to any intensity light. The question arises now for how long can a film be exposed to safelight illumination before fog becomes apparent.

Processing Tanks

Tank processing is the simplest and most efficient procedure for developing, rinsing, fixing and washing films with accurate temperature control.

Two parts:

a) Master Tank – It serves as water jacket to hold the insert tanks. Made of either enamel, stainless steel or plastic (no reactive metals), it should be large enough to provide space between insert tanks for rinsing and washing of films.

b) Insert Tanks – Removable containers for the individual processing solutions (developer and fixer) that are made of stainless steel. They are kept spaced in the master tank.

The processing tanks should be supplied with covers. Lid should have a large lip to reduce exposure to light and air (oxygen). Cover the developer and fixer tanks when not in use to keep out dirt and reduce the rate of evaporation and oxidation.

The fresh water tank plays an important role in temperature control, as well as eliminating the alkali (Na2CO3) from the developer and the acid (acetic) from the fixer solution.

Hot and Cold Running Water

A temperature of 20 °C for 5 minutes is recommended for obtaining optimum quality of radiographs. Processing time is practical i.e. 5 minutes, and can be conveniently maintained.

Temperature of the water in the water tank is controlled by a thermostatic or manual mixing valve in the water supply. Temperature of water in the master tank in turn controls the temperature of the solutions in the insert tanks.

Thermometer and Interval Timer

Tank thermometer: A plainly marked thermometer with both Centigrade and Fahrenheit scales, that has a steel clip that forms a hook to hang it (or a floating type).

Interval timer: It is used to control time of development and fixation.

Ventilation

If development and drying are done in the same room, then ventilation should be provided to supply the room with fresh air, and for eliminating the heated air from the dryer. Suitable drying racks should be present where no automatic dryer is present

Storage Place

An appropriate storage area for chemicals and films is mandatory. It should not be a general store room. Processing rooms cannot be used as storage rooms.

Viewing Area

A radiographic viewer is used in the darkroom, when making use of the techniques of time temperature (wet viewing), and to examine the final product.

Dose Limits

Workers:Cumulative effective dose over a block of five years shall not exceed 100 mSvEffective dose in any calendar year during a five-year block shall not exceed 30 mSv

Trainees:Effective dose in any calendar year shall not exceed 6 mSv

Public:Effective dose in any calendar year shall not exceed 1 mSvEffective dose averaged over a five year period does not exceed 1 mSv/year

Conclusion

To quote Aristotle, “Well begun is half done.”

The proper designing of the radiographic room, and more importantly the dark room, is essential to obtaining diagnostic quality radiographs, with minimal safety concerns and maximum use of resources.

References

1) P. E. S. Palmer. Manual of Darkroom Technique. WHO Basic Radiological System. 1985.

2) Neill Serman. The Darkroom. August 2000.3) Darkroom and Film Processing. RAD TECH A.4) AERB Safety Code for Medical Diagnostic X-ray Equipment and Installations. NO.

AERB/SC/MED-2 (Rev. 1)5) Indian Dental Association (IDA) Guidelines6) Directorate of Radiation Safety (DRS) Guidelines7) Guidance Notes for Dental Practitioners on the Safe Use of X-Ray Equipment.

Department of Health. National Radiological Protection Board – 2001.