The System Of Radiation Protection

(according to ARPANSA RPS1 and IAEA SSS 115 (BSS) - both adopted from ICRU 60)

Practices
things that create an exposure to radiation (beyond naturally occurring)
Intervention
things done to reduce an exposure
Accident
an unintented event that [potentially] causes an exposure
Potential Exposure
the root of an accident, the system of protection aims to minimise these in terms of probability and magnitude. The product of a possible exposure and its probability can be used as an actual dose value for modelling of for instance shielding.

3 types of exposure

  • Occupational (there is an exclusion list ie, natural background )
  • Public (does not include naturally occurring exposure)
  • Medical (diagnostic or therapy patients and their carers, research volunteers. Dose limits do not apply to this type of exposure but justification and optimisation do)

Control these exposures ‘at the source’ (by shielding or containment, ALARA prescription), by designing the environment (ventilation, distances between equipment etc) and with the use of PPE (lead aprons etc)

The 3 core principles of the system should be applied to all practices:

  • Justification (net benefit is obtained by performing the exposure, improving techniques can improve the justification of a practice)
  • Optimization (minimise the doses given, the people exposed and potential exposures… basically the application of ALARA)
  • Dose Limits (an upper bound value to limit the risk to a person. Due to the statistical nature of it all, these can be broken in some circumstances and can be hard define ‘unsafe’ levels)

Implementing the System of Radiation Protection
*Compliance should be a condition of obtaining a licence.
*Authorisation from all relevant bodies is needed to undertake operations. Exemptions can be sought.
*Authorities, operators, employers and employees all have responsibilities.
*Employers are responsible for providing induction and training.
*Occupational and medical exposures can usually be controlled at the source, in the environment and through personal protective equipment.
*Controlled areas are where dose is more than public limit over a year, or where a potential accident would lead to deterministic effects.
*Employers are responsible for ensuring a Radiation Monitoring Program is developed and followed

Supplement to RPS1
*A standard for limitation of occupational exposures - how to optimise exposure in the workplace.

From RPS1 supplement (p.11) (bold is my emphasis)

Equipment calibration – Radiotherapy
3.1.25 The Responsible Person must ensure that:
(a) all radiation-producing therapy equipment and remote afterloading brachytherapy equipment is calibrated for the proposed clinical techniques by a qualified expert at the time of acceptance following installation;
(b) before release for clinical use, all radiation-producing therapy equipment and remote afterloading brachytherapy equipment is subjected to an independent series of calibration tests for the proposed clinical techniques that confirm that the conditions under which it was calibrated produce acceptable clinical accuracy of dose output;
(c) clinical use of radiation-producing therapy equipment and remote afterloading brachytherapy equipment is restricted to those techniques for which the equipment has been calibrated and independently checked as described in (a) and (b);
(d) each of the clinically-used treatment beams for radiation producing therapy equipment and all clinical parameters for equipment containing radioactive sources (in relation to both planning and treatment delivery) are checked and recalibrated by a qualified expert at intervals specified in national or international protocols;
(e) all calibrations of reference and radiation-measuring equipment are traceable to relevant national standards.

Radiotherapy treatment planning
3.1.26 The Responsible Person must ensure that all dosimetry data used for
treatment planning:
(a) are clearly documented; and
(b) have a reference trace to the original data source.

3.1.27 The Responsible Person must ensure that:
(a) the treatment planning procedures are followed;
(b) all treatment planning equipment is tested;
(c) the basic data for each available treatment planning computer program are verified by a qualified expert:
(i) on initial acceptance; and
(ii) after any change or upgrade; and
(d) patient-specific independent calculations of monitor units or treatment time are performed for radiotherapy.

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