1. Design, Layout and Shielding of Medical Facilities
Day 8 – Lecture 1

2. Objective
To become familiar with the safety requirements for the design of medical facilities
To understand the principles of shielding and other radiation safety measures.

3. Contents Controlled and supervised areas; Design criteria:
Radiotherapy;
Nuclear Medicine;
Diagnostic and Interventional Radiology;

4. Basic Concepts Locating and siting sources (GSR Part 3, 3.51)
“When choosing a location to use or to store a radiation generator or radioactive source, registrants and licensees shall take into account:
factors that that could affect the safe management of and control over the radiation generator or radioactive source;
factors that could affect occupational exposure and public exposure due to the radiation generator or radioactive source; and
the feasibility of taking the foregoing factors into account in engineering design.”

5. Basic Concepts (cont.) Controlled area
“A defined area in which specific protection measures and safety provisions are or could be required for controlling exposures or preventing the spread of contamination in normal working conditions, and preventing or limiting the extent of potential exposures.” (GSR Part 3 Definitions).
Example: radiotherapy, controlled areas include:
all treatment rooms;
brachytherapy source preparation rooms;
source storage areas.

6. Basic Concepts (cont.) Supervised area
“A defined area not designated as a controlled area but for which occupational exposure conditions are kept under review, even though no specific protection measures or safety provisions are not normally needed..”
(GSR Part 3 Definitions).
Example: radiotherapy supervised areas include:
operator consoles (shielded);
locations where calculated exposure rates through barriers may result in doses of 1mSv per year (IAEA TECDOC1040, 1998).

7. Basic Concepts (cont.) Controlled and Supervised areas Require:
restricted access;
warning signs;
staff monitoring;
interlocks, where appropriate;
written work and emergency procedures.

8. Radiotherapy Radiotherapy Design criteria Shielding Barriers
Secondary radiation sources
Neutrons
Sky shine
Construction follow-up
References

9. Design criteria
In radiotherapy, potentially lethal doses of radiation are delivered to patients.
In order to avoid misadministration and to minimize the exposure of other individuals (staff, visitors, general public) a radiotherapy facility must be appropriately designed. Shielding is an essential part of this design process.

10. Radiotherapy facility
The radiotherapy facility is likely to comprise:
reception areas;
clinic rooms – to assess and review patients;
waiting areas;
diagnostic area - e.g. CT scanner, simulator, dark room;
treatment units – e.g. 60Co, linacs, superficial / orthovoltage, HDR brachytherapy;
treatment planning and mould room;
dosimetry, physics and electronics areas;
office space and storage.

11. Brachytherapy treatment area
A brachytherapy treatment area is likely to comprise:
a shielded room (for manual or remote afterloading treatments);
dosimetry and physics area;
source preparation area may be required (e.g. 192Ir wire cutting);
source storage (including emergency storage arrangements);
nurses’ station with patient intercom (audio and visual preferable).

12. Design criteria for new facilities
Some design criteria for new facilities
When planning a new facility the assumptions made (i.e. workload, types of treatments, sources etc) must be clearly stated.
The licensee must plan for the future and consider expansion and an increase in the workload.
Size matters. The area allocated to treatment rooms should be generous (inverse square law).
Effective and inexpensive shielding can be obtained by locating megavoltage treatment rooms in the basement.
Bunkers should be placed together to make use of common shielding walls.

13. Design criteria – External beam therapy
Some design criteria – external beam therapy
Carefully consider:
the placement of the treatment unit;
the direction(s) of the primary beam;
the location of the operator;
surrounding areas to ensure low occupancy.
costs:
can be reduced through careful design;
of extensions can be large (i.e. consider the provision for expansion during the initial building phase).

14. Design criteria – external beam therapy (cont)
Some design criteria – external beam therapy (cont)
Clear warning signs are required in areas leading to treatment units.
Patient and visitor waiting areas should be positioned so that no person is likely to enter a treatment area accidentally.
Patient change areas should be located so that the patient is unlikely to enter a treatment area accidentally.
Appropriate shielding must be provided to comply with the public dose limits and any additional public dose constraints.

15. Design in treatment rooms
Features of good design in treatment rooms
Interlocks
The possibility of accidental exposure can be minimized by measures such as interlocks involving (possibly in combination):
a door;
a gate (barrier);
light beams (that trigger alarms, stop exposures, return sources to a shielded condition, etc);
audible alarms.

16. Design in treatment rooms (cont)
Features of good design in treatment rooms (cont)
Emergency “off” buttons

17. Shielding
Aim: To restrict radiation doses to staff, patients, visitors and the public to acceptable levels.
Different considerations apply to:
superficial / orthovoltage x-ray units ;
simulators (see diagnostic and interventional radiology course);
60Co units;
linear accelerators;
brachytherapy.

18. Shielding (cont)
must be designed with the advice of a qualified expert.
The regulator’s role is to:
verify the assumptions and design criteria (e.g. the use of appropriate occupational and public dose limits and values) are appropriate;
ensure that the design has been checked by a qualified expert;
approve the design (assuming it is satisfactory).
Assumptions must be based on justifiable estimates. Conservative assumptions should be used as under-shielding is significantly worse (and more costly) than over-shielding.

19. Shielding (cont) Types of shielding materials
Low energy gamma and x-rays - lead; compare with diagnostic applications.
High energy (> 500 keV) gamma and x-rays - concrete (cheaper and self supporting), high density concrete.
Electrons - usually shielded appropriately if photon shielding is appropriate.

20. Barriers
Primary
barrier
Secondary
Maze

21. Secondary radiation sources
Secondary radiation sources – external beam therapy
Leakage:
depends on equipment design; typically limited to 0.1 to 0.2% of the intensity of the primary beam;
originates from the radiation source.
Scatter:
is assumed to come from the patient although patient scatter may be less than 0.1% of the intensity of the useful beam at 1 metre;
may be difficult to calculate (use the largest field size and a scatter phantom for measurements).

22. Neutrons
Determining neutron doses is a complex issue requiring the services of a qualified expert.
Neutrons are produced by (γ,n) production from high energy accelerators (E > 10 MV)
Example:
“A measurement of neutron dose at an accelerator voltage of 18 MV gave an estimate of 4 mSv per therapy Gray at a distance of 1 meter from the target.”
Radiation Protection. A Guide for Scientists, Regulators and Physicians.
J Shapiro. 4th edition, 2002.

23. Neutrons (cont)
Neutron activation following the use of high energy photons will contribute to the radiation dose received by persons entering the treatment room.
The typical half life of activation products is short with the most likely elements to be activated being oxygen and nitrogen i.e. 16O (photon,n) 15O, t1/2 = 2 minutes; 14N (photon,n) 13N, t1/2 = 10minutes.
A waiting period of about one minute will reduce the activated radiation levels to approximately one-half.

24. Sky shine
Sky shine is a term given to radiation scattered from the air above the treatment room.
If the roof of a treatment facility is not occupied (and if there are no adjacent structures for which protection is required), licensees may be tempted to minimize the roof shielding.
However, this source of scattered radiation can substantially increase the exposure to persons in adjoining areas.
When assessing applications for linear accelerators, the potential contribution of sky shine to occupational and public doses should be considered.

25. Construction follow-up
It is essential to verify that construction proceeds as planned and approved by the Regulatory Authority. The integrity of the shielding must be assessed during construction (through inspections by the qualified expert and RPO) and after installation of the treatment unit (by radiation surveys).
Flaws may be in the execution rather than the design.
Assumptions used in the design must be verified and regularly reviewed.

26. References
IAEA TECDOC 1040
NCRP Report 49
NCRP Report 51

27. Nuclear Medicine Nuclear Medicine Defense in depth Facilities
Categorization of the Hazard
Floors
Ventilation
Patient Toilet
Layout of a Nuclear Medicine Department
Safety Equipment

28. Nuclear Medicine Defence in Depth Weak points? Source
Hospital
Nuclear Medicine Department
Radiopharmaceutical laboratory
Work area
Shielded container
Source
This is to illustrate the concept of defense in depth. A source is contained in a shield to prevent from external exposure. If contamination occur it should be kept within the work area, the laboratory, the department or at least in the hospital.
Weak points? Identify situations where the defense in depth will fail, meaning that we have to introduce a different safety concept or special requirements. Weak points are exhaust of volatile radionuclides through the fume hood directly out in the air and disposal of sources via the sewage system. Another weak point is the living source (patient) leaving the hospital.
Weak points?

29. Facilities
The design of facilities should take into consideration the type of work and the radionuclides and their activities intended to be used. The concept of ‘categorization of hazard’ should be used in order to determine the special needs concerning ventilation, plumbing, materials used in walls, floors and work benches.
The radiation protection officer (RPO) should be consulted as soon as the planning process commences for construction or renovation of a nuclear medicine facility or other hospital radioisotope laboratory.

30. Categorization of Hazard
Categorization of the hazard should be based on:
calculation of a weighted activity using weighting factors according to radionuclide used and the type of operation performed.
Weighted activity Category
< 50 MBq Low hazard
50 MBq - 50 GBq Medium hazard
> 50 GBq High hazard
This is an introduction to the ICRP concept of categorization of hazard which should be used to define some basic building requirements.

31. Categorization of Hazard (cont)
Weighting factors according to type of operation
Type of operation or area Weighting factor
Storage
Waste handling, imaging room (no injection),
waiting area, patient bed area (diagnostic) 0.10
Local dispensing, radionuclide administration,
imaging room (injection), simple preparation,
patient bed area (therapy)
Complex preparation

32. Categorization of Hazard (cont)
Areas not frequented by patients
High hazard
Room for preparation and dispensing radiopharmaceuticals.
Temporary storage of waste.
Medium hazard
Room for storage of radionuclides.
Low hazard
Room for measuring samples.
Radiochemical work (RIA).
Offices.
These are examples of categorization of hazard for different rooms in a typical nuclear medicine department handling quite large amounts of Tc99m

33. Categorization of Hazard (cont)
Areas frequented by patients
High hazard
Room for administration of radiopharmaceuticals.
Examination room.
Isolation ward.
Medium hazard
Waiting room.
Patient toilet.
Low hazard
Reception.

34. Floors No carpet! Impervious material. Washable. Chemical-resistant.
Coved to the walls.
All joints sealed.
Glued to the floor.
No carpet!

35. Ventilation Sterile room negative pressure filtered air Injection room
Dispensation
Corridor
Injection
room
Fume hood
Laminar air
flow cabinets
Passage
Work bench
Rooms where work with unsealed sources are taken place should be under negative pressure to minimize the risk of airborne radionuclides to be spread, The sterile environment that might be necessary in preparation of radiopharmaceuticals is achieved in a laminar air flow bench.

36. Patient Toilet
A separate toilet room for the exclusive use of injected patients is recommended.
A sign requesting patients to flush the toilet well and wash their hands should be displayed to ensure adequate dilution of excreted radioactive materials and minimize contamination.
The facilities shall include a wash-up sink as a normal hygiene measure.

37. Layout of a Nuclear Medicine Department
From high to low activity
This illustration is from a Nuclear Medicine department in India. Does it follow the general rule to separate high activity areas from low activity areas and to separate working areas from patient areas?

38. Safety Equipment Shields. Protective clothing.
Tools for remote handling of radioactive material.
Containers for radioactive waste.
Dose rate monitor with alarm.
Contamination monitor.
Decontamination kit.
Signs, labels and records.

39. Diagnostic and Interventional Radiology
Sources of Potential Exposure
A Typical X-Ray Room

40. Sources of potential exposure
It is a fundamental assumption that x-ray equipment and its associated facilities will be designed and installed so as to minimize the risk of staff and the public (other than patients) being exposed to the unattenuated primary (useful) x-ray beam.
The remaining two radiation sources against which users and the public must be protected are:
leakage radiation from the x-ray tube assembly;
and
scattered radiation (primarily from the patient).

41. Sources of potential exposure (cont)
The potential radiation dose that might be received by users and the public depends on:
the effectiveness of the shielding between them and the radiation source;
their distance from the source; and
the nature and volume of the x-ray workload.
Note: The potential for individuals to receive a radiation dose from more than one source or at more than one location should be considered i.e. in determining the effectiveness of shielding it should not be assumed that the facility under review is the sole facility possibly contributing to an individual’s exposure.

42. Sources of potential exposure (cont)
Limits on leakage radiation are prescribed in standards e.g.
for diagnostic x-ray tube assemblies (including collimators) is 1 mGy in 1 h at 1 m at every power rating specified by the manufacturer;
for dental intraoral x-ray tube assemblies (including collimators); 0.25 mGy in 1 h at 1 m is recommended; and
for mammography x-ray tube assemblies (including collimators), an additional limit of 0.01 mGy per 100 mAs at 0.30 m from the side of the assembly facing the patient;
Note: Limits on leakage are based on the total potential dose at the prescribed distance when the x-ray tube is operated at any of the manufacturer's ratings (usually at the maximum kVp) for a period of 1 hour. Leakage may be measured by integrating air kerma over a brief exposure of seconds or as a rate measurement (e.g. µGy/hr at 1m) but both measurements must be corrected for the time the x-ray tube assembly can operate at the selected exposure factors without exceeding the manufacturer’s heat limits.
e.g. Assume that leakage from a mobile x-ray unit operating at 120 kVp and 100 mA is measured with an ion chamber survey meter as 8000 µGy/h at 1m. However, from the manufacturer’s specifications, it has been determined that the maximum continuous current for that x-ray tube in that tube assembly at 120 kVp is 5 mA.
Therefore, the potential accumulated dose from leakage over one hour’s (intermittent) operation is then (5/100)*8000 µGy or 0.4 mGy, below the prescribed limit of 1 mGy in 1 hr at 1m.

43. Sources of potential exposure (cont)
Scattered radiation
arises from any object within the x-ray beam (including, but to a very limited extent in diagnostic radiology, the air through which the primary x-ray beam passes);
the intensity of scatter is dependent on a number of factors, including the intensity of the primary (useful) x-ray beam, the area of the x-ray beam incident on the patient and the angle from the primary beam at which scatter is assessed.

44. A Typical X-ray Room An x-ray room should:
have adequate safety provisions to minimize the probability of accidental exposures;
Toilet
be designed so that safety systems or devices are inherent to the equipment or the room;
take into account the working area required; be appropriate to the types of examinations to be performed and the type of x-ray equipment to be used.
Dark Room
X-ray Room
Control