5 CT Shielding Design - VA Seattle - CT Rm 2D-150D - Mar 2022.pdf

Radiation Shielding Design Calculations March 7th, 2022 VA Seattle GE Revolution APEX – CT Room 2D-150D

Radiation Shield Design

GE REVOLUTION APEX – CT SCANNER

(CT ROOM 2D-150D)

3/7/2022

VA PUGET SOUND HEALTHCARE SYSTEM

1660 S. COLUMBIAN WAY

SEATTLE, WA 98108

Joby Voetberg, MHP, DABR Medical Physicist joby@corwinhp.com

GE Revolution with APEX – CT Room 2D-150D

Shielding Design Summary

Shielding calculations were performed for a GE Revolution with APEX CT scanner that will be installed in at VA Puget Sound Healthcare in Seattle, Washington in Room 2D- 150D. This scanner is replacing a GE Discovery 750 HD 64 slice scanner that is currently in use in the same room.

Please note, this room has existing shielding. The existing shielding was determined by measuring lead on core samples provided by the facility. Some of the existing lead is adequate. The new walls and any area where the existing lead is removed or modified requires additional lead to that which is specified.

Summary of Required Shielding

A summary chart of the required shielding is at enclosure 1. A scale drawing of the room is at enclosure 2. The following lead shielding is the minimum amount of lead required to reduce radiation exposures to below the current regulatory limits. Installation of lead thickness greater than those specified below is acceptable. Note: Unless noted, all shielding must extend from the floor to a height of 7 feet.

Control Wall, Window, and Door- Wall A. The Control Wall, Window, and Door require 1.58 mm lead shielding. This wall is being moved from the original configuration of the room, so it will require additional lead shielding.

Break Room Wall - Wall B. This wall requires 1.58 mm lead along the walls facing the scanner (see Diagram of Room for approximate placement). Note: The core sample taken along this wall did not reveal any lead shielding. Please see the Core Sample Floorplan for locations of core samples and found lead shielding. Its recommended that additional samples be taken from this wall to confirm there is not lead present. If no lead is found, additional lead will be required.

Corridor C2-36 - Wall C. This wall requires 1.58 mm lead shielding along the entire length. This wall is being moved from the original configuration of the room, so it will require additional lead shielding.

H.A.C Wall - Wall D. This wall contains 1.58 mm lead shielding. Additional shielding is not required. Note: the wall connecting Corridor C2-36 wall and the H.A.C. wall does not require lead as it will be shielded from scatter.

Corridor Wall – Wall E. Core samples revealed this wall contains 1.98 mm lead shielding. Additional shielding is not required.

Corridor Door. This door must contain 1.58 mm lead or greater. Please field verify the existing lead is at least 1.58 mm lead in thickness.

Patient Prep Wall – Wall F. Core samples revealed this wall contains 1.98 mm lead shielding. Additional shielding is not required.

Patient Prep Door. This door must contain 1.58 mm lead or greater. Please field verify the existing lead is at least 1.58 mm lead in thickness.

Ceiling and Floor. No additional shielding is required on the ceiling or floor. The spaces immediately above/below this room are interstitial spaces with low occupancy.

The floor to floor distance of these spaces is about 6 feet. Calculations were done for the occupied spaces above/below the interstitial space. The construction of each floor is about 4 1/2 inches concrete (per information provided by the facility). Therefore, the existing construction between this room and the occupied floors above/below would be 8- 9 inches concrete.

Methods and Assumptions

The above shielding recommendations were based on the following information:

The proposed x-ray system is a GE Revolution with APEX Computed Tomography system. Scatter radiation diagrams are enclosed.

The maximum weekly exposure rates for controlled areas are 0.10 mGy/week and for uncontrolled areas is 0.02 mGy/week.

The estimated workload of approximately 40 patients per day (200 patients per work week) was provided by the center. The occupancy of each room is noted on the enclosed detailed summary sheet and diagram. A total of mA-min per week was used in the shield calculations. This included a 40% increase to body studies to take into account multiphase contrast exams. This also included a 15% increase to the workload to account for potential growth.

The mA minutes above are based on approximate techniques used for head and body exams. Since this is a new model of scanner, specific clinical techniques to be used were not available. The techniques used to determine workload were a conservative estimate based on similar GE scanners. The scatter diagram provided by GE was modified by the 120 kVp correction factor (0.71) since it can be assumed most scans will be performed using 120 kVp.

Core samples provided by the facility revealed existing lead in some, but not all walls. Please see the Core Sample Floorplan for approximate locations of lead found in the original layout of this room. New walls, and any area where the existing lead is removed or modified requires additional lead to that which is specified.

The primary reference for these shielding calculations is NCRP Report 147, Structural Shielding Design for Medical X-Ray Imaging Facilities.

Please note the following:

These recommendations are based on the workload and occupancy of rooms provided at the time of these shielding design calculations. If changes occur in the occupancy of the rooms next to this x-ray room, if the type of x-ray system is changed, or if the workload increases, additional shielding may be required.

The existing shielding was determined from information provided by the facility. If the existing shielding is different than noted, additional lead may be required.

Please keep a copy of this shielding plan at your facility indefinitely.

Thank-you for allowing me to perform your shielding calculations. If you have any questions, please call me at (360) 736-6066.

Joseph (Joby) L. Voetberg, MHP, DABR Medical Physicist

CORWIN HEALTH PHYSICS INC

Enclosures:

Shielding Summaries Diagram of Room Core Sample Floorplan Manufacturer Scatter Survey Diagrams Appendix A – Recommendations for Shielding Penetrations Appendix B – Schedule of Commercial Lead Shielding

Typical kVp

GE Revolution Apex - Room 2D-150D 2D-150D 120 12,069

Thickness (mm) Type Control Wall, Window and Door Wall A Secondary Controlled 1 5.79 1.13 Lead None 1.58 mm Lead Break Room Wall Wall B Secondary Uncontrolled 1/5 4.19 1.54 Lead None 1.58 mm Lead Corridor C2-36 Wall C Secondary Uncontrolled 1/5 3.66 1.51 Lead None 1.58 mm Lead H.A.C Wall Wall D Secondary Uncontrolled 1/20 2.44 1.28 Lead 1.58 mm Lead None Corridor Wall Wall E Secondary Uncontrolled 1/5 2.82 1.73 Lead 1.98 mm Lead None Corridor Door N/A Secondary Uncontrolled 1/8 4.11 0.23 Lead None 1.58 mm Lead Patient Prep Wall Wall F Secondary Uncontrolled 1/20 4.42 0.98 Lead 1.98 mm Lead None Patient Prep Door N/A Secondary Uncontrolled 1/8 4.42 1.31 Lead None 1.58 mm Lead Floor N/A Secondary Uncontrolled 1 4.88 135.24 Concrete ~200 mm Concrete None Ceiling N/A Secondary Uncontrolled 1 5.03 133.64 Concrete ~200 mm Concrete None

Notes:

Lead thickness greater than the above specified is acceptable. Unless specified, all shielding must extend from the floor to a height of seven feet.

Please see the detailed Shielding Design Summary for further guidance.

Existing Shielding

Summary of Shielding Calculations Puget Sound VA Hospital

GE Revolution Apex - Room 2D-150D

March 7th, 2022

Patients per Week

The Isodose Method was used.

Type of X-Ray Machine Room ID Workload Information mA-min/wk

The body exams include 40% increase due to contrast studies.

A projected 15% workload increase was also included in the above mA-minutes

Ceiling/Floor: The spaces immediately above/below this room are interstitial spaces with low occupancy. The floor to floor distance of these spaces is about 6 feet. Calculations were done for the occupied spaces above/below the interstitial space. The construction of each floor is about 4 1/2 inches concrete (per information provided by the facility). Therefore, the existing construction between this room and the occupied floors above/below would be 8-9 inches concrete.

Existing Shielding: Core samples provided by the facility revealed existing lead in some, but not all walls. Please see the Core Sample Floorplan for approximate locations of lead found in the original layout of this room. New walls, and any area where the existing lead is removed or modified requires additional lead to that which is specified.

Primary or Secondary

Shielding Specifications

Calculated Shielding Additional Shielding RequiredDistance to

Space (m) Occupancy

Factor Type of

OccupancyWall DescriptionWall Description

Diagram of Room – Room 2D-150D

March 2022

Control Wall, Window, and Door- Wall A. The Control Wall, Window, and Door require 1.58 mm lead shielding. This wall is being moved from the original configuration of the room, so it will require additional lead shielding.

Break Room Wall - Wall B.

This wall requires 1.58 mm lead along the walls facing the scanner. See report summary for additional information.

Corridor C2-36 - Wall C.

This wall requires 1.58 mm lead shielding along the entire length.

H.A.C Wall - Wall D. This wall contains 1.58 mm lead shielding. Additional shielding is not required. Note: the wall connecting Corridor C2-36 wall and the H.A.C. wall does not require lead as it will be shielded from scatter.

Corridor Wall - Wall E. Core samples revealed this wall contains

1.98 mm lead shielding.

Additional shielding is not required.

Corridor Door.

This door must contain 1.58 mm lead or greater.

Patient Prep Wall - Wall F.

Core samples revealed this wall contains 1.98 mm lead shielding. Additional shielding is not required.

Patient Prep Door. This door must contain 1.58 mm lead or greater.

Ceiling and Floor. No additional shielding is required on the ceiling or floor. The spaces immediately above/below this room are interstitial spaces with low occupancy, and with approximately 8-9 inches of concrete. Please see the report summary for additional information.

1.58 mm Lead

Core Sample Floorplan

CT 2D-150D and 2D150E March 2022

CT-1: 1.98 mm Lead CT-2: 1.98 mm Lead CT-3: 1.58 mm Lead CT-4: No lead observed in core sample CT-5: 1.98 mm Lead

Appendix A – Recommendations for Shielding Penetrations

Shielding Screw/Nails: Penetrations made by screws/nails do not require lead “tabs” to cover the top of the screws/nails. The steel nails/screws generally attenuate radiation equally, or more effectively than the lead displaced by the screws/nails.

Shielding Joints: The joints between lead sheets should be constructed so that their surfaces are in contact with an overlap of not less than 1 cm. This can be accomplished by using lead battens, or by using drywall that is manufactured with the lead sheet extending beyond the edge of the drywall for adequate overlap.

Shielding Penetrations: Air conditioning ducts, electrical conduit, plumbing, and other infrastructure will penetrate shielded walls, floors, and ceilings. The shielding of the x-ray room shall be so constructed that the protection is not impaired by these openings or by service boxes, etc., embedded in barriers. The duct/conduit shielding thickness shall be equivalent to the displaced shielding thickness. Below are general shielding details for duct/pipe penetrations into a shielded surface where H is the diameter of the penetration.

1. Straight pipe/conduit penetration: Situations where there is a straight pipe/conduit penetrating a lead shielded surface require lead to line (wrap) the pipe/conduit twice the distance as the diameter/thickness of the pipe or conduit. See Detail 1 below.

Detail 1:

2. Curved elbow penetration: Situations where there is a curved pipe/conduit penetrating lead shielding requires lead to line (wrap) to line the entire top/backside of the elbow and pipe for 3 times the distance of the diameter of the opening. See Detail 2 below.

Detail 2:

3. Flat Panel Penetrations (electrical panels etc.). Flat panel penetrations can be shielded by either wrapping the entire structure (panel/box) being installed or by shielding behind the panel/box. If the lead shielding is installed behind the panel, the lead must extend beyond each side of the panel (penetration) by twice the thickness of the wall. For example, if the wall is 4 inches thick, the lead shielding must extend 8 inches beyond each edge of the cut-out section of the wall.

4. 90 degree elbow running out of the wall: Situations where there is a 90 degree elbow penetrating a lead shielded surface requires lead to line the top of the elbow up to the 90 degree turn, and then the back side of the pipe for twice the distance of the diameter/thickness of the pipe PLUS the thickness of the wall. See Detail 3 below:

Detail 3:

The above recommendations and details are adequate for shielding most common shielding penetrations. There may be exceptions where these methods are not appropriate for providing adequate radiation protection. Please contact Corwin Health Physics if there are other questions on how to appropriately shield a space.

Reference: The primary reference for these recommendations is NCRP Report 147.

Appendix B – Schedule of Commercial Lead Shielding

Thickness (mm)

Thickness (inches)

Weight in Pounds per Square Foot (PSF)

0.79 1/32 2

1.00 5/128 2.5

1.19 3/64 3

1.58 1/16 4

1.98 5/64 5

2.38 3/32 6

3.00 -- 7.5

3.17 1/8 8

3.97 5/32 10

4.76 3/16 12

5.55 7/32 13

6.35 1/4 16

8.47 1/3 20

9.52 3/8 24

12.70 1/2 30

19.05 3/4 45

25.40 1 60