The plan approval process has two main objectives:
The plan approval process is performed to ensure that no individual, either in the course of their work or in the vicinity of the x-ray machine, is subjected to radiation exposure in excess of their applicable maximum permissible dose equivalents as per the HARP Regulation, Section 3 (1), which states:
"Every installation of an x-ray machine shall be shielded with a primary protective barrier and.a secondary protective barrier so that,
(a) no x-ray worker receives a whole-body-dose-equivalent of more than 1 millisievert (100 millirem) per week; and
(b) no person, other than the patient undergoing an application of therapeutic or diagnostic x-rays, who is not an x-ray worker, receives a whole-body-dose-equivalent of more than 0.1 millisievert (10 millirems) per week"
The plan approval process is performed to ensure that all medical x-ray owners in Ontario abide by Section 3 of the Healing Arts Radiation Protection (HARP) Act.
The Act states:
"No person shall install an x-ray machine unless the Director has issued written approval for the installation."
Legislated Requirements
The following are excerpts from the Healing Arts Radiation Protection (HARP) Act and Regulation regarding plan approval.
Section 3 (2) of the HARP Act states:
"Subject to subsection (3), any person who applies accordance with the Act and the regulations for written approval for the installation of any x-ray machine and,
is entitled to be issued written approval."
Section 2 ( 1 ) of the HARP Regulation states:
The following information is prescribed for the purpose of clause 3 (2)(a) of the Act:
Section 2 (2) of the HARP Regulation states:
"The following plan, to be submitted in duplicate, is prescribed for the purpose of clause 3 (2)(a) of the Act:
1. A floor plan drawn to a scale of not less than one to fifty that indicates,
Section 2 (3) of the HARP Regulation states:
"In addition to the requirements prescribed in subsection (2) where the application for approval is for the installation of an x-ray machine in a dental facility, the floor plans shall indicate,
(a) the position and limits of rotation of the chair, and
(b) the position of the head of the person being irradiated."
In order to obtain written approval, the applicant must submit to the X-Ray Inspection Service (XRIS) plans, specifications, and information as prescribed in Section 3 (2) of the HARP Act and Sections 2 (1), 2 (2) and 2 (3) of the Regulation as stated previously. The following is a list of items that must be included with the submission for plan approval:
NOTE:
Submissions that do not meet one or more of the following requirements will be returned WITHOUT approval.
Form 2
A properly completed Form 2 includes the following:
Form 3
A properly completed Form 3 for each room which will contain an x-ray machine. The Form 3 must include the following information:
Plans must be submitted in duplicate. The following items must appear on the plan to allow for the completion of the radiation shielding process:
Note:
Plan approval manual with calculation charts can be obtained from the X-ray Inspection Service (416) 327-7937.
After plans and forms have been submitted they are reviewed and processed accordingly. If plans and forms are properly completed the plan is approved.
Label
After a plan has been approved the label is attached to the approved plan and signed by the Director of X-Ray Safety. Read the label carefully and note any instructions which may pertain to your approved plan.
Plan Rejection Letter
There are many common problems associated with plan approval submissions. These problems have been summarized in a form letter that is included with returned plans that are rejected. Review the plan rejection letter carefully and note the checked items which pertain to your submission. The rejection letter includes a list of information required on Form 2, Form(s) 3 and the plans that were not included or incomplete in the submission. In addition, any area where radiation safety (eg. areas subject to scatter ratiation) is a concern is noted in this form letter.
Plan Approval Letter
When plans have been approved they are returned accompanied by a letter. This form letter will indicate any further action that may be required by the facility. Please read this letter carefully upon receipt of your approved plans and note the areas that have been identified for your submission.
In order to obtain written approval, the applicant must submit to the X-Ray Inspection Service (XRIS) plans, specifications, and information as prescribed in Section 3 (2) of the HARP Act and Sections 2 (1), 2 (2) and 2 (3) of the Regulation as stated previously. The following is a list of items that must be included with the submission for plan approval:
NOTE: Submissions that do not meet one or more of the following requirements will be returned WITHOUT approval.
Form 2
A properly completed Form 2 includes the following:
Form 3
A properly completed Form 3 for each room which will contain an x-ray machine. The Form 3 must include the following information:
25 This is not the maximum mA of the x-ray machine. It is the milliamperage which can be sustained across the filament.
26 Radiographic, Fluoroscopic and Auxiliary tubes must be documented separately.
Plans must be submitted in duplicate. The following items must appear on the plan to allow for the completion of the radiation shielding process:
Canada Communications Group
Publishing
Ottawa, Ontario, Canada K1A 0S9
Tel: (819) 956-4800
Fax: (819) 994-1498
Copies of Appendix II of Safety Code 20A may also be obtained from the X-Ray Inspection Service with a Plan Approval Kit.
After plans and forms have been submitted they are reviewed and processed accordingly. If plans and forms are properly completed the plan is approved if no additional shielding is required.
The radiation shielding indicated for the barriers on the Form(s) 3 and the plans are acceptable and no changes to the proposed shielding are required.
The following is a list of common symbols and notations commonly used which may be made on the plans.
# no occupancy permitted during exposure
* doors marked * must be equipped with self- closing device and warning sign required
Note:
The symbols above are the common symbols used by the X-Ray Inspection Service. Other symbols may be used when necessary. Please refer to the legend on the approved plan for their meanings.
After a plan has been approved the label is attached to the approved plan and signed by the Director of X-Ray Safety. Read the label carefully and note any instructions which may pertain to your approved plan.
There are many common problems with regard to plan approval submissions. These problems have been summarized in a form letter that is included with retumed plans that are rejected. Please review the plan rejection letter carefully and note the areas checked regarding your submission. The rejection letter includes a list of information required on Form 2, Form(s) 3 and the plans that are not included or incomplete in the submission. In addition, areas where radiation safety is a concem is noted in this form letter.
When plans have been approved they are returned with a letter. This form letter will indicate what further action if any may be required by the facility. A sample of this letter may be found in Appendix II, Example 3. Please read this letter carefully upon receipt of your approved plans and note the areas that have been checked regarding your submission.
|
Dental Plan - Sample Dr. J.J. Johnson 123 Your Street Suite 102 Anytown, Ontario M4H-1A8 Legend All walls constructed of 2x1/2" drywall unless stated otherwise.
Note: Plan is not to scale.
|
|
|
Medical Plan - Sample Dr. J. Smith 333 Jones Avenue Suite 203 Anytown, Ontario N2N-1N1 Note: Plans not to scale to allow for inclusion in the manual. |
|
UFS - 1.6 mm lead lined unused film storage
Above x-ray room - Lab
Below x-ray room - Doctor's Office
Construction and Shielding (All lead sheets from the floor to 7 feet high) Floor - 203.2 mm of concrete
Ceiling - 203.2 mm concrete
A -Control booth wall: 1.6 mm lead added to 25.4 mm (1") drywall
B -Control booth window: 0.5 mm lead glass
C -Chest Stand: 0.8 mm lead equivalent
D -West Wall: 1.6 mm lead added to 25.4 mm (1") drywall
E -South Wall and Doors: 0.8 mm lead added to 25.4 mm (1 ") drywall
F -East Wall: 1.6 mm lead added to 25.4 mm (1") drywall
X -Exposure Switch
+ -X-Ray head normal position
O -X-Ray head limits of movement
* -Door equipped with self-closing device and warning signs
Radiographic Workload
10 (patients/day) x 3(films/patient) x 6(days a week) x 100 milliamperes x 1 second)
-------------------------------------------------------------------------------------------------------------
60 (seconds)
= 300 mAmin/week
Fluoroscopic Workload
3 (patients/day) x 3(minutes of exam time per patient) x 6 (days a week) x 1.5 millamperes
= 81 mAmin/week
For a primary protective barriers, the value of K can be computed from the following equation:
K = Pd2/WUT
where:
P = maximum permissible weekly exposure rate expressed in R/week. For controlled areas P = 0.1 R/week; for uncontrolled areas P = 0.01 R/week.
d = distance in metres from target to the primary area.
W = workload in mA-min/week.
U = use factor.
T = occupancy factor.
K = exposure per unit workload at unit distance, in R/mA-min at 1 metre.
Use the appropriate graphs on pages 59, 60 and 61 of Safety Code 20A to determine the primary barrier thickness required in conjunction with the above equation.
Radiographic Tube - Floor Calculation
K = Pd2/WUT = .01 x (3.66) 2/300(.75)(1) = 0.133956/225 = .000595
From the Graph on page 59 and page 6, 2 mm of Lead or 19 cm of concrete is required
Radiographic Tube - West Wall (Chest Stand)
K =Pd2/WUT = .01 x (1.98) 2/300(.25)(1) = .039204/75 = .000523
From the Graph on page 59 - Require 2.3 mm of Lead
Secondary Barrier Calculations
Secondary barriers are required to protect against both leakage and scaRered radiation.
Barrier against Leakage Radiation
To determine the barrier thickness required to protect against leakage radiation it is necessary to calculate the transmission factor, B, required to reduce the weekly exposure to P. The formula used is as follows:
B = 600 IPd2/WT
where:
P = maximum permissible weekly exposure rate, expressed in R/week. For controlled areas P = 0.1 R/week; for uncontrolled areas P = 0.01 R/week.
d = distance in metres from the tube housing to the secondary barrier.
I = tube current in milliamperes
W = workload in mA-min/week.
T = occupancy factor.
Once the transmission factor, B is determined, the barrier thickness can be determined form figure 3 in Safety Code 20A as a number of half-value layers, N or tenth-value layers, n. The required barrier thickness in mm of lead or cm of concrete can then be determined from Table 6 on page 57 of Safety Code 20A.
Barrier against Scatter Radiation
For a scatter barrier the value for K can be determined from the formula:
K = 400Pd2D2/aWTF
where:
K = exposure per unit workload at 1 metre, expressed in R per mA-min at 1 m.
P = maximum permissible weekly exposure rate expressed in R/week. For controlled areas P = 0.1 R/week; for uncontrolled areas P = 0.01 R/week.
d = distance in metres from the target to the scatterer.
D = distance in metres from the scatterer to the secondary barrier.
a = ratio of scattered to incident exposure (Tabulated in Table 8 of Safety Code 20A) Note: For calculations purposes a 90ø angle is always used.
W = workload in mA-min/week.
T = occupancy factor.
F = field area in cm2.
Use the appropriate graphs on pages 59, 60 and 61 of Safety Code 20A to determine the primary barrier thickness required in conjunction with the above equation.
Example:
Secondary Barriers required for Plan Approval (Example 3 above)
Secondary Barrier - East Wall
|
Radiographic K=400Pd2D2/aWTF K=400(.01)(.8) 2(3.38) 2/.0016(300)(1)(1535) K=0.0397 From Graph on page 59 0.7mm Lead Required |
Fluoroscopic K=400Pd2D2/aWTF K=400(.01)(.5) 2(3.38) 2/.0016(81)(1)(775) K=0.11374 From Graph on page 59 0.2mm Lead Required |
Leakage Barrier - East Wall
|
Radiographic B=600IPd2/WT B=600(1.5)(0.01)(3.38)2/300(1) B=0.342732 |
Fluoroscopic B=600IPd2/WT B=600(1.5)(0.01)(3.38)2/81(1) B=1.26938 |
In the above example, the transmission values for the radiographic and fluoroscopic tubes respectively was 0.34 and 1.27. Referring to Appendix II of Safety Code 20A, these values correspond to 1.2 HVLs for Radiography and 0 HVLs for Fluoroscopy. From Table 6, the HVL for 150 kVp is 0.30 mm Lead. Thus, the required barrier thickness for protection against radiation is:
Therefore, a total of 0.9 mm Lead is required for the scatter barrier.
Radiography: (1.2 x 0.30) = 0.36 mm Lead
Fluoroscopy: (0 x 0.30) = 0 mm Lead
Therefore, the leakage barrier calculations determine that a total of 0.36 mm Lead is required as a Leakage Barrier.
When the barrier thicknesses for leakage and scattered radiation differ by at least 1 Tenth-Value Layer (TVL), the thicker of the two will be adequate. If they differ by less than 1 TVL, 1 Half Value-Layer (HVL) should be added to the thicker measurement to obtain the required total secondary barrier thickness. From our calculations, the thicker of the two barriers (scatter barrier) calculated does not differ from the other barrier (leakage) by greater than one TVL. One TVL at 150 kVp is 0.99 mm lead. Therefore, because the two calculated values do not differ by greater than 0.99 mm lead, one HVL must be added to the measurement for scatter radiation to obtain the required total secondary barrier thickness.
1 HVL at 150 kVp is 0.30 mm Lead
Therefore, total barrier thickness required for the East Wall is 0.90 mm Lead plus 0.30 mm Lead for a total barrier thickness of 1.2 mm Lead.
These calculations are provided for example purposes only. They are not complete as they do not include calculation for the south and north walls, the floor and the ceiling.
The following figures present standard area measurements for different imaging modalities.
Field Size in cm2
Radiographic 1535 cm2 Fluoroscopic 9" 500 cm2 Fluoroscopic 12" 730 cm2 Spot Film 775 cm2 Mammographic 775 cm2 CT 50 cm2
Distances normally used in metres from the target to the scatterer.
Radiographic (bucky work) 40" 0.8 m Radiographic (chest stand) 72" 1.6 m Fluoroscopic 0.5 m Mammographic 0.6 m CT 0.8 m
Notes:
1. The distance to the primary or secondary barrier required in the calculatins is measured from the location where the tube is normally used. The normal place to take the measurement is over the centre of the table for medical x-ray tubes and the normal tube position for chiropractic facilities.
2. The distance used as a default for floor and ceiling Barrier calculations is 12 feet. Should this distance be different at your facility, it must be documented on the plans.
