B01 Attachment J10 - Physicist Report.pdf

Location: Lawton Indian Hospital 1515 Lawrie Tatum Rd

Lawton, OK 73507

Equipment: SIEMENS X.Cite

Date: 7/6/2020

Summary: A shielding evaluation for a new installation of an CT scanner was requested. Detailed plans of the CT equipment installation were obtained, and the expected use case for this equipment was discussed with the Radiology Supervisor. The portion of the building housing the CT is single-story, with no rooms above or below the room being examined.

The CT room shares walls with corridors to the north, west, and south, and the CT/MRI control room to the east.

This document contains the assumptions, parameters, and calculations used to determine the minimum shielding requirements for a CT scanner, based on the formalism published in NCRP 147, “Structural Shielding Design for Medical X-Ray Imaging Facilities.”

The assumptions used should be reviewed for accuracy. Should errors exist, the shielding design will need to be re-evaluated. In cases where uncertainties exist, conservative assumptions were made to bias the final answer toward increased safety for radiation workers as well as members of the public.

Assumptions:

• The calculations were performed assuming one hundred and twenty-five (125) patients per week. It is recognized that the actual workload will often be less than this, but shielding is constructed to accommodate this number as a maximum.

• This number of exams is assumed to consist of a 3:1 ratio of single- and multi-phase procedures (e.g., with and without contrast), representing head and body exams, respectively.

• Although the architectural drawings show a dual-use corridor/patient waiting area to the southwest of the CT room, an occupancy factor corresponding to a corridor (1/5) was used for the barrier thickness calculations for the south and west walls due to it’s higher, and thus, more conservative value relative to an unattended patient waiting area (1/20).

Radiation Protection Shielding Design - CT

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Recommendations:

Barrier Considered: Minimum Additional Shielding Required:

1. North wall (corridor) 1/32” Pb

2. North CT door 1/64” Pb leaded door

3. East wall (CT/MRI control) 1/32” Pb

4. East Viewing window (CT/MRI control) 1/32” Pb lead-equivalent glass

5. South CT door 1/32” Pb leaded door

6. South wall (corridor/patient waiting) 3/64” Pb

7. West wall (corridor/patient waiting) 1/32” Pb

8. Ceiling None

9. Floor None

Note: The values for lead (Pb) thickness are given in fractional inches for convenience, as most commercially available lead products are manufactured using fractional inch thicknesses.

Additionally, the values above are the smallest fractional inch values that are greater than the necessary Pb thicknesses calculated below. For the sake of convenience, thicker lead may be used than is recommended above. For example, 1/16” lead could be used on every wall for simplicity of installation, wider availability of material, and/or cost effectiveness. Installing ‘more than enough’ lead during initial construction also allows for ample growth in the number

P a g e 3 | 4 of scans that can be conducted at the facility without raising any concerns of future shielding adequacy.

Final Evaluation of Radiation Protection:

After construction is underway and walls have been placed (if necessary), please perform or arrange for a mid-construction evaluation. This should be done prior to finishing the walls so that the shielding used can be confirmed. Following construction, a final radiation protection survey may be desirable to confirm that the shielding provided will achieve the shielding design goals.

Notes to Contractor:

• Shielding should extend to a minimum height of 2.1m (7 ft) from the floor.

• Penetrations in protective barriers, such as those for electrical conduit, plumbing, and other infrastructure, should be created so as to not impair shielding properties. This may involve backing or baffling penetrations with supplementary lead shielding.

• Joints between lead sheets should be constructed so that their surfaces are in contact, with an overlap of not less than 1 cm.

• A permanent placard should be mounted in the room specifying the amount and type of shielding in each of the walls.

Should you have any questions about this shielding design report, or require any other radiation protection services, please do not hesitate to contact me.

Respectfully submitted by:

David Klein, PhD DABR Medical Physicist, Partner

Scissortail Medical Physics, LLC 6129 S. Louisville Ave Tulsa, OK 74136 918-280-8483 dave@scissortailphysics.com

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