SPECT CT_Complete Shielding Report.pdf

LBT Diagnostic Radiation Physics Consulting Ltd Phillip W Patton, PhD CHP DABR

Department of Veterans Affairs VAMC

VA Medical Center Memphis

1030 Jefferson Avenue

Memphis, Tennessee 38104

Report of the Radiation Shielding Calculations

For the PET/CT Room CW101D

May 13, 2020

Phillip W Patton, PhD, CHP, DABR, DABSNM

LBT Radiation Physics Consulting, Ltd.

2608 Morning Cloud Lane

Las Vegas, NV 89142

702-336-3004

Discussion

In general, calculated shielding is often overestimated due to assumptions on workload, use factors and occupancy factors. I have attempted to provide more realistic factors based on information from the facility and modified occupancy estimates. The workload is set high enough to allow for any minor increases without requiring further shielding. Extensive use of helical scanning is considered in the workload estimate.

Radiation protection is based on three concepts: time, distance, and shielding. All three are used to maintain radiation exposures in the workplace at or below safe levels. The maximum weekly exposure currently allowed for occupationally exposed workers is 100 millirem (controlled areas) and for non-occupationally exposed workers (uncontrolled areas) is 2 millirem. Therefore to apply the ALARA concept, shielding design exposure limits are 10 mR/week for controlled areas and 2 mR/week for uncontrolled areas.

All lead sheeting should extend to a height of at least 7 feet above floor level. Nail heads do not need to be overlapped. Overlying drywall seams should be offset and great care should be exercised in taping and plastering the seams. No gaps or holes in drywall are acceptable.

The calculations were completed using the vendor’s supplied dose lines for CT, an average dose of

20 mCi for each patient, and an average of 10 patients per week.

Figure 1 shows the layout of the PET-CT room. Final results are presented on page 4 for the PET

CT room.

Any questions concerning this report may be directed to Phillip Patton 702-336-3004

Performed by:

Phillip W Patton, PhD CHP, DABR, DABSNM

Diagnostic Medical Physicist, References

(1) National Council on Radiation Protection and Measurements (NCRP) Report 147, Structural

Shielding Design for Medical X-ray Imaging Facilities, NCRP, 2004

Figure 1. The PET -CT room CW101D layout.

Table 1. Shielding recommendations for the PET-CT scanner.

Based upon the above calculations and professional judgement, the following recommendations for shielding are made:

Barrier Recommended Shielding

A-B Control Room Wall Recommend 1/16" lead in this barrier, door, and window.

B-C Corridor Wall Recommend 1/16" lead in this barrier.

C-D Outside Wall Recommend 1/16" lead in this barrier.

D-E Hot Lab Wall Recommend 1/16" lead in this barrier.

E-F-A Corridor Wall Recommend 1/16" lead in this barrier and door.

Ceiling No additional shielding required.

Summary

Department of Veterans Affairs VAMC VA Medical Center Memphis

1030 Jefferson Avenue Memphis, Tennessee 38104

Shielding Survey of New CT Room

Surveyed: September 22, 2020 Report: September 22, 2020

Phillip W Patton, PhD, CHP, DABR

LBT Radiation Physics Consulting, Ltd.

2608 Morning Cloud Lane

Las Vegas, NV 89142 702-336-3004

The facility was inspected on September 22, 2020 to determine the amount of x-ray shielding provided by existing walls. Figure 1 shows the room with survey points labeled. The room was tested using a Tc-99m source to check for existing shielding integrity and equivalent lead thickness. The data is shown below in table 1.

Figure 1: D100 room with existing walls in Nuclear Medicine and measurement locations

G109

Glass

Control Room window Door

D102

OR Hallway

H al lw ay

C or rid or

Door

Do or

New Cath Lab

Ad ja ce nt

C at hl ab

D

A

C

E

B

Table 1: Data for survey results of shielding integrity

Discussion Radiation protection is based on three concepts: time, distance, and shielding. All three are used to maintain radiation exposures in the workplace at or below safe levels. The maximum weekly exposure currently allowed is 100 millirem (0.1mGy) for occupationally exposed workers (restricted area) and 2 millirem (0.02mGy) (average) for non-occupationally exposed workers (unrestricted area). In keeping with the ALARA concept, shielding design dose limits are 10 mR/week for restricted areas and 2 mR/week for unrestricted areas.

The exiting door had no measurable lead shielding.

As can be seen in the data, there appears to be at least 1/8” lead equivalent in all existing walls/barriers for this room. The survey should be repeated after any significant changes to the walls.

Any questions concerning this report may be directed to Phillip Patton 702-336-3004

Performed by:

Robert O'Brien, PhD, DABSNM Medical Physicist

Date Performed: 22-Sep-20

Site Dist (m) from source Exposure (mR/hr) Barrier Lead Equivalent STD 0.45 12.7 Air

A 0.45 0.01 Gypsum + Lead 1/8" B 0.45 6.90 Wood Unshielded C 0.45 0.01 Gypsum + Lead 1/8" D 0.45 0.01 Gypsum + Lead 1/8" E 0.45 0.01 Gypsum + Lead 1/8"

Resources used for measurements:

Source: Tc99m 50.7mCi Source

12.7 mR/hr at 45cm Detector: Unfors Xi

Probe: S/N: 179369

Cal. Due: 7/8/2021

Testing Performed 30cm from wall, In Accordance with NCRP 147

In Air Exposure: