(The complete text of these radiation regulations may be purchased from Singapore National Printers)
Premises using radiation sources or storing radioactive materials are subject to inspections to ensure compliance with safety requirements. Safety inspections are carried out before a new radiation facility can be put to use, and routine inspections are conducted for existing facilities at least once a year or once in two years. The main checks during an inspection visit are to ensure that:
- the radiation sources are all licensed, the details are correct and they are all properly maintained;
- all the radiation sources are physically accounted for;
- there is a suitably qualified person licensed to use the radiation source;
- the radiation level outside the room housing the radiation source, at any location accessible to any individual, should not be more than 10 µSv/hr, when the irradiating apparatus is working at its maximum rating or when the radioactive source is exposed;
- the radiation warning signs are prominently displayed; and
- the interlock system for the door is functioning; and for medical facilities
- that QA programs are in place, with proper documentation
For a work site in an open area, a barricade with the radiation hazard logo, has to be placed around the work area. The radiation level at this barricade should not be more than 25 µSv/hr.
QA checks are particularly important in radiotherapy as high doses of radiation are delivered to the patient. The aim of the QA Program is to ensure optimal accuracy in the delivery of prescribed radiation dose to the patient undergoing therapy treatment and to minimise radiation risks to others. The Radiotherapy Centre’s QA Program and its results must be documented and made available for auditing by RPNSD at any time.
Records of the daily, monthly and annual QA checks performed are inspected. The daily QA checks done are:
- laser alignment to isocentre;
- accuracy of optical distance indicator;
- x-ray output constancy at all energies;
- electron output constancy; and
- door interlock, warning light and audiovisual monitor are functional.
The monthly checks to be performed by physicists are:
- laser alignment to isocentre;
- gantry and collimator angle indicator;
- field size indicator (for the whole range of field sizes);
- light/radiation field congruence;
- mechanical gantry isocentre;
- collimator rotation axis;
- cross-hair centre-ing;
- jaw symmetry;
- output calibration;
- x-ray field flatness constancy;
- x-ray field symmetry constancy;
- electron beam field symmetry constancy;
- x-ray beam energy constancy;
- backup monitor constancy (MU1/MU2);
- checking that the wedge/accessory interlock, electron cone/field size interlock,
- treatment couch brake/lock, x-ray/electron interlock, and the collision device (if available) are all functioning.
Annually, the service engineer should do all the mechanical and electrical tests recommended by the manufacturer to ensure that the machine is still in good working condition. The accuracy or constancy of all the above checks should be within 2 to 3 per cent.
In addition, all patient treatment records, treatment planning and dose data should be properly maintained for auditing and inspections.
Medical diagnostic and dental X-ray facilities
QA Programs are also necessary for medical diagnostic and dental x-ray facilities.
Although the dose given in medical diagnostic and dental x-rays is relatively low, almost every individual would have undergone this type of examination sometime in his or her lifetime. Collectively, we want to keep the dose to the population as low as possible so it is important that the correct dose be given for each radiograph. Guidance dose levels for medical diagnostic radiography for a typical adult patient, as recommended by the IBSS, are given in the following table. The given doses should not be too low either because then, the radiograph may not show the requested diagnostic information and the patient will not get the expected medical benefit from the x-ray examination. There shall be proper documentation of all QA procedures.
It is important that all QA procedures are properly documented.
|Guidance dose levels for medical diagnostic radiography for a typical adult patient
||Entrance surface dose per radiograph* (mGy)
|Abdomen, intravenous urography and cholecystography
PA: posterior-anterior projection
LAT: lateral projection
AP: anterior-posterior projection.
* In air with backscatter. These values are for conventional film-screen combination in the relative speed of 200. For high speed film-screen combinations (400 - 600), the values should be reduced by a factor of 2 to 3.
An inspection for a medical diagnostic facility would therefore include the general checks outlined above and the existence of a comprehensive QA Program, which should include:
- image quality assessment;
- film-reject analysis;
- patient dose evaluation;
- measurements of the physical parameters of the radiation generators (e.g. kVp, mAs) and imaging devices (e.g. film processors) at the time of commissioning and periodically thereafter;
- verification of the appropriate physical and clinical factors used in patient diagnosis;
- written records of relevant procedures and results;
- verification of the appropriate calibration and conditions of operation of dosimetry and monitoring equipment;
- procedures for remedial actions, follow-up and result evaluation.
QA measurements to check that the equipment continues to meet manufacturer’s specifications should be done annually by trained staff from the supplier.
Nuclear medicine facilities
For nuclear medicine facilities and laboratories using radionuclides, in addition to the above general checks, the facilities for storage and dispensing of radionuclides will be inspected as well as the facilities for storage and disposal of radioactive waste.
The QA Program for Nuclear Medicine should include QA for radiopharmaceuticals as well as QA for the equipment. For radiopharmaceuticals intended for administration to patients, there should be an acquisition protocol to ensure that it meets the clinical requirements and satisfies both radiation safety and pharmaceutical quality requirements. There shall be proper documentation of all QA and QC procedures.
Proper records shall be maintained for types and quantities of radionuclides in stock and used. Patient records shall also be kept together with details of radionuclides and radiopharmaceuticals administered. Records shall also be maintained for storage of radioactive waste and their disposal.