What is radiation safety in radiology?

These Regulations were first implemented in 1974. They were amended in 2000 to incorporate the 1990 Recommendations of the International Commission on Radiological Protection (ICRP) and the requirements of the International Basic Safety Standards (IBSS) published in 1996 by the International Atomic Energy Agency (IAEA). The main requirements under these radiation regulations are explained below.

General requirements

No one below the age of 18 years may be engaged in radiation work. Any one engaged in radiation work must have a licence or be registered as a radiation worker and he should wear a personal monitoring device to monitor the amount of radiation received in the course of his work. Within 12 months prior to his application, he must have undergone a medical examination, which includes a full blood examination and certified fit to be engaged in radiation work by a registered medical practitioner.

Licensing

Licences are issued by RPNSD under the Radiation Protection Act 2007 and the Radiation Protection (Ionising Radiation) Regulations 2000 for the import, export, sale, dealing in, possession and use of radioactive materials and irradiating apparatus and the transport of radioactive materials.

Application forms must be completed and submitted to RPNSD with the appropriate payment – except for consignment licences, which are applied for through the TradeNet System.

With effect from 28 May 2018. hardcopy licence application forms for new licences and renewal, amendment or cancellation of licences under the Radiation Protection Act will be replaced by online application forms to be submitted through LicenceOne. Consignment licences should continue to be applied for through the TradeNet System.

A separate licence is required to keep or possess each irradiating apparatus. Agents who import irradiating apparatus or radioactive materials for sale or re-export, must give RPNSD an accounting at the end of each month, stating the irradiating apparatus or radioactive materials they have imported, exported, sold locally (including the name of the buyer) and those remaining in their possession.

The exemption limits for the licensing of radioactive materials are taken from the IBSS. They are given in terms of activity and activity concentration for each radionuclide.

To ensure that the irradiating apparatus and radioactive materials are used safely, only those with the necessary qualifications and knowledge in radiation safety for the work intended under the licence or can prove that they have special knowledge of the safe use or application of the radiation sources, may be granted licences to use them.

For example, licences to use irradiating apparatus for medical diagnostic purposes may be granted only to qualified diagnostic radiologists. For industrial purposes, the licence applicant must show documentary proof that he is knowledgeable in radiation safety or take a test set by RPNSD. The licensee is allowed to use only the irradiating apparatus or radioactive material specified in his licence.

RPNSD may cancel or suspend any licence if the licensee infringes the Radiation Protection Act or its Regulations.

Exemptions

Any educational institution which has in its possession or under its control any radioactive substance, being a sealed source, not exceeding 100 times the activity or activity concentration prescribed in the First Schedule of the Radiation Protection (Ionising Radiation) Regulations with respect to that particular radioactive substance, and any teacher designated under this paragraph, shall be exempted from possession, use and transport under the Radiation Protection Act and its subsidiary legislation if —
(a) the radioactive substance is used or to be used solely for demonstration, teaching or research purposes in the educational institution;
(b) the radioactive substance is under the control of a competent teacher designated by the principal in the case of a secondary school, or by the head of the relevant department, in the case of a university, polytechnic or college, to take full responsibility for the safe storage and use of such radioactive substance and for the compliance with the relevant provisions of these Regulations relating to a sealed source; and
(c) the name of the teacher designated in accordance with sub‑paragraph (b) and the complete details of the radioactive substance are submitted to the RPNSD.

Any person who has in their possession or under their control not more than 3 sealed sources, each of which contains any radioactive substance not exceeding 175 kBq, for the sole purpose of checking or calibrating a particular radiation survey or monitoring instrument shall be exempted from possession, use and transport under the Radiation Protection Act and its subsidiary legislation if the complete details of the radioactive substance are submitted to the RPNSD, except that the person shall be responsible for the safe storage and use of the radioactive substance and for compliance with the relevant provisions of these Regulations relating to a sealed source.

Control of radiation exposure

Any person who has or uses irradiating apparatus or radioactive materials may not cause another person to receive a radiation dose greater than what may be justified under the circumstances, and not more than the annual dose limit. The licensee must ensure that radiation work is performed safely.

Dose limits, medical and radiological supervision

For radiation workers, the limit on the effective dose to the whole body is 20 mSv a year averaged over five years, and that the effective dose should not exceed 50 mSv in any one year. For members of the public, the effective dose limit to the whole body is 1 mSv per year.

If the dose report indicates that the worker has received a dose in excess of the dose limit, his employer must send him for a medical examination which includes a full blood examination. The employee will also be suspended from radiation work for an appropriate period of time. Investigations will be made by the licensee and RPNSD to ascertain the cause of the excessive dose and measures must be taken to ensure that the accident or incident does not happen again.

The occupational dose limit for women who are not pregnant is the same as that for men. But once the pregnancy is declared, the equivalent dose limit to the surface of the woman’s abdomen shall be 2 mSv for the rest of the pregnancy.

All the above dose limits do not include the dose from any medical or dental exposure as a patient or from the exposure to natural background.

Labelling of radiation sources and radiation areas

The licensee should ensure that each irradiating apparatus and each container of radioactive material is properly labelled with the radiation hazard logo. Any premises with radioactive materials or where radiation work is being performed should display the radiation hazard logo and other appropriate signs and notices placed at prominent positions.

When the radiation hazard ceases to exist, all the labels and notices should be removed.

Storage of radioactive materials

Radioactive materials should be stored in a safe and secured place. Only the licensee and the radiation workers under his charge may have access to the radioactive materials. Outside the defined area where the radioactive materials are stored, the radiation levels must not exceed 0.5 µSv/hr. Precautions for the safe storage and keeping of radioactive materials are also specified, including specifications for storage containers, fire and chemical safety etc.

Accounting of radioactive materials

Licensees should keep proper records of radioactive materials used by them and under their charge e.g. the date of receipt, the nature and form, the activity of the radioactive material at the date specified by the manufacturer, the whereabouts of the radioactive material at any time etc.

If the radioactive material is missing and is not accounted for within 24 hours, the licensee must notify RPNSD.

Checking of leakage of sealed source

Once in every 12 months, a wipe test must be performed on each sealed radioactive source to ensure that it is not leaking.

If it is found to be leaking, RPNSD must be immediately informed and the source must be removed and stored in a proper manner. It must not be brought back into use until all necessary repairs have been effected. The areas affected by the leakage must be decontaminated under the supervision of RPNSD.

Use of sealed sources and irradiating apparatus in industrial radiography

For a radiation source in a walled enclosure or a cabinet, the radiation level anywhere outside the walled enclosure or cabinet, accessible to anyone, should not be more than 10 µSv/hr.

For radiation work in a field site, a boundary must be set up and clearly defined by ropes, fences, walls of buildings etc., and the radiation hazard logo and warning notices incorporating the words “DANGER – RADIATION”, such that the radiation level outside the boundary should not exceed 25 µSv/hr. There should be continuous and competent supervision of the site whenever a sealed source is exposed or an irradiating apparatus is energised within the site. A survey meter should be available and used at the field site to check the radiation level boundary requirement and that the radiation source has returned to the OFF condition immediately on completion of each exposure.

Any radiation area monitor, survey meter or direct reading personal dosimeter used for any purpose in connection with the Regulations, must be calibrated once every 12 months.

Use of irradiating apparatus for medical, dental and veterinary diagnostic purposes

The X-ray room should have sufficient space to provide safe accommodation for everyone who is in the room. The walls and the door of the X-ray room should have adequate thickness or adequately lead-lined such that when the machine is operated at its maximum rated current for the maximum rated voltage and at its normal operating positions, the radiation level outside the room, at any position accessible to anyone, should not exceed 10 µSv/hr.

There should be a red light placed at a conspicuous place outside the X-ray room, which must be switched on whenever the X-ray machine is being used to deter the entry of anyone not connected with the X-ray examination.

Lead gloves, lead aprons and lead screens must be available for the protection of staff and patients. The field size should be limited to the area of interest and, unless inappropriate for the technique employed, fast films and intensifying screens must be used so that the irradiation of the patient is not more than is necessary to produce a satisfactory diagnostic result.

If a weak patient or child has to be supported during the X-ray examination, or a dental film has to be held for a patient, mechanical devices may be used as far as is practicable, otherwise the person rendering such assistance must be provided with protective clothing and be positioned so as to avoid the primary beam. This person cannot be a radiation worker, a pregnant woman or a person below the age of 18 years.

Similarly, an animal must not be held by anyone unless other means of immobilisation are impracticable. If manual restraint is necessary, the animal must be held down by a minimum number of people who are not staff of the veterinary establishment, not pregnant and not below the age of 18 years. If it is necessary for the animal to be held by members of the veterinary establishment, only those who have been registered as radiation workers and have been trained for such purposes may be so employed and they will be provided with protective clothing and be positioned so as to avoid the primary beam.

Protective clothing like lead aprons must be examined visually frequently and examined radiographically at least annually to ensure that the protection afforded has not been impaired as a result of cracks in the material.

Use of irradiation for medical therapeutic purposes

The radiation treatment room must have sufficient space to provide safe accommodation for everyone in the room. The walls and door of the radiation treatment room should have adequate thickness to provide protection against the primary beam and the secondary radiation so that the radiation level at any location outside this radiation treatment room, accessible to anyone, does not exceed 10 µSv/hr when the radiation source inside is on.

The control panel should be outside and there must be a warning red light placed in a conspicuous position, both inside and outside the radiation treatment room. These red lights must be on whenever the radiation source is on. Means must be provided for observing the patient during treatment and for communication between the patient in the treatment room and the operator at the control panel outside.

The door of the treatment room must be fitted with an interlocking device and the radiation source must be provided with a device which will automatically terminate the treatment after a preset time or radiation dose.

Use of radioactive sources for medical purposes

Any hospital or medical institution using sealed or unsealed sources for medical purposes must be equipped with suitable radiation monitors or survey meters.

Hospitalised patients undergoing treatment with any sealed or unsealed source must be accommodated in dedicated rooms with a warning notice on the door. If the radiation level at one metre from the patient exceeds 20 µSv/hr, the radiation hazard logo and a notice containing any necessary nursing precautions must be attached to the bed.

Admittance to the room should be strictly controlled and the patient cannot leave the room without the approval of the radiologist in charge of the treatment.

Any temporary implant of a sealed source, including a nuclear battery used to power a cardiac pacemaker, must be removed from a corpse before the corpse is disposed of.

No post mortem examination, cremation or embalming process should be carried out on a corpse known to contain a sealed or unsealed source without approval from RPNSD or the Medical Director of the hospital responsible for the implanting of the sealed source.

Use of unsealed sources in medical, industrial and research installations and in educational institutions

All installations and institutions where unsealed radioactive substances are used or handled must have adequate facilities where appropriate for radioisotope storage, preparation, administration, monitoring and counting.

All work surfaces must be made of non-porous and non-reactive material such as stainless steel. A fume cupboard may be provided to perform operations likely to produce radioactive contamination of the air through the production of aerosols, smoke or vapours.

All radioisotope laboratories or workrooms must be adequately ventilated and be provided with washing facilities suitable for decontamination purposes.

The dos and don’ts of working in a radioisotope laboratory are stated in the Regulations. Contaminated items for disposal must be put in special plastic bags and this radioactive waste must be put in a radioactive storage room.

Radiation accidents

Radiation accidents in medical and non-medical applications of ionising radiation or radioactive materials are defined in the Regulations.

In a non-medical application, a radiation accident is considered to have occurred if an unplanned, uncontrolled high level of radiation occurs, such a lost radioactive source, or damage of the radiation shielding of a sealed radioactive source or irradiating apparatus; or a person enters a high radiation field by accident; or if there is a spillage or leakage of unsealed radioactive material causing contamination; or if radioactive material is accidentally released into the environment in excess of the permitted discharge level.

In medical application, a radiation accident is considered to have occurred if any therapeutic treatment is delivered to the wrong patient or to the wrong tissue of any patient; or if the patient is treated with a dose or dose fractionation which differs by more than 10 per cent from the value prescribed by the radiologist in charge of the treatment; or if the wrong radiopharmaceutical is used. A radiation accident is also considered to have occurred if any diagnostic exposure given is 50 per cent greater than the intended dose or if the patient receives a dose significantly different from that which was intended.

If an accident should occur, the actions to be taken by the licensees or safety officers are spelt out. The licensee has to notify the appropriate authorities and in all cases, the licensee must notify RPNSD and give a preliminary oral report of the accident within 24 hours, which is to be confirmed in writing within 48 hours and a full written report of the accident within 10 days.

The schedules

The First Schedule gives a table of the licensing exemption limits for each radionuclide in terms of maximum activities and activity concentrations. The Second Schedule gives the dose limits for radiation workers and for members of the public. The Third Schedule tabulates the annual limits on intake (ALI) for radiation workers, the Fourth Schedule shows the radiation hazard logo and the Fifth Schedule gives the limits for contamination of surfaces.

Unlicensed radioactive sources

In the event that any individual encounters a suspected unlicensed radioactive source, please contact NEA via the online feedback form (https://www.nea.gov.sg/corporate-functions/feedback) or myENV app. Members of the public are advised to minimize physical contact with the suspected radioactive source. Radioactive sources should not be disposed of without authorization from NEA.

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