Is More Pb the Answer in a Changing Medical Environment?

Presented by

Dawn Banghart, CHP

Stanford University

Has a doctor ever told you …

We will only do 4 PET/CT studies per day. Maximum.

We will replace the simulator with a PET/CT and will only use it for overflow studies. Its primary use will be after-hours research.

There will never be a PET/CT in this room, just a CT. Really.

You are leaving for vacation and get this phone call … We are purchasing a new,

self-shielded, portable intraoperative electron linear accelerator therapy unit. It will be located in our existing OR suite. Does it need any additional shielding?

It’s Monday. You are getting this Physician’s Email … We are considering replacing our 3 GE gamma cameras

with 3 new cameras, each one having a low-dose CT option. If we replace them, can we still put all three cameras in the same open room? We need a response by Thursday.

The room layout:

Chief Tech’s Office

Current gamma camera locations

Control panels

Introduction

A rapidly changing medical environment includes upgraded diagnostic machines such as Mobile CT and Therapy units Increasing PET/CT demands On-site cyclotrons and facility retrofits

Shielding calculations and considerations are made against the backdrop of Budget issues Project timelines Existing space Pressures to increase patient load.

Topics to be covered

This presentation will: Summarize the changing landscape of Stanford University’s

medical machines and facilities in the past 10 years. Share and discuss specific shielding projects (the good, the bad

and the ugly). Focus mainly on PET patients and diagnostic machines with the

exception of one exotic therapy machine.

TodayTomorrow

Stanford CTs: A Snapshot10 years Ago and Now

CTs 1997 CTs 2007

2 Stanford Hospital 3 Stanford Hospital

1 Blake Wilbur Clinic 2 VA Palo Alto

1 SU Children’s Hospital

1 Blake Wilbur Clinic

1 SU Children’s Hospital

1 Blake Wilbur Trailer in parking lot

1 Mobile unit in ER parking lot

1 SU Nuc Med Hospital Hawkeye

1 Cath/Angio CT-Fluoro (for biopsy – patient/table moves)

1 VA Palo Alto CT/fluoro combo ((~ first in USA, each moves independent of the other)

5 total

12 total

What’s in the pipeline

New CT Projects in various stages of review

2 CTs California Ave Satellite facility

3 CTs Redwood City Satellite Facility (plus x-ray suite)

6 CTs SU Nuclear Medicine New Facility (3 PET/CT, 3 SPECT/CT)

1 CereTom Portable CT for Children’s Hospital

3 CTs VA Palo Alto to replace gamma cameras

1 Cath/Angio Fluoro/CT (inverse of above – arm moves)

1 SU Hospital Surgery – Combination MRI and CT

1 Head and Neck Surgery (C-arm-like CT – bed moves)

18 More!

Additional growth measures:

Portable C-arms 3 in 1997 17 in 2007

Cyclotron Installation (completed in late 2005)

Nuclides Produced

2007

(Ci)

2008

(Ci)

Projected

F-18 2300 6000

C-11 11 1500

N-13 160 300

Consider increases as more PET/CTs come online.

PET/CT Patient load increasesPositron Emitters can’t be ignored We have

Observed significant patient study increases. Learned that doctors are not the best resource

when considering their changing future. They consistently underestimate patient workloads.

F-18, while not a machine, with a 4 mm half-value layer, is a walking concern in our waiting rooms and for our doctors and technicians.

PET/CT Shielding Calc tools:

Site Evaluation: Use of adjacent spaces (including

above and below injection room and uptake room).

Get architectural drawings as soon as you learn about the project.

We find that obtaining drawings can take weeks and often the needed information (e.g., cross-sections) needs to be requested repeatedly

Spreadsheets are our friend!

Injection Rooms:

AAPM 108

Injection Wall E    

F-18 half life 110 min

N = 40patients/ week

Gamma Constant F-18 Patient 0.34

(mrem/h)/mCim2

T 1.0  

d 2.1 m

AAPM Task Group 108: PET and PET/CT Shielding Requirements includes guidance on: Decay correction for dose integration period). Patient F-18 shielding

PET Patient Basics –

PET patients use positron emitters (emits 511 KeV photon)

The patient associated dose rate depends on: Number of patients/week Procedure time

Uptake time: 1 hour Scanning time: 0.5 hour

Administered activity 10 - 20 mCi

Note: Minimal facility shielding is required where clinics have large rooms (greater than 3 meters)

Comparison between F-18 and the Tc99m “workhorse”

 

HVL (mm)

KeV

Typical dose rate

from patient (mrem/hr)

F-18 4 511 5

Tc99m <1 141 0.7

PET Patient workload increases

As described by the Stanford Hospital Nuclear Medicine Chief Tech:

When we first began, we did up to six patient's a day with one tech.

We currently schedule 12-15 patient's a day with one scanner and two techs.

As described by the VA Palo Alto Nuclear Medicine Chief Tech:

Started operations with new machine May 7, 2006.

Began with 4 patients per day now doing 7.

We were dosing one per hour, but since June 07, we are “batching” one patient every 30 minutes in the morning.

PET Patient Load Increase

0

2

4

6

8

10

12

14

16

SU Nuclear Medicine VA Nuclear Medicine

Start of operationsNow

PatientsPer Day

Is Stanford’s experience common?What the experts have observed:

“Clinical imaging exams in the US increased almost 600 percent from 1980 to 2006. In the past, natural background radiation was the leading source of human exposure; that has been displaced by diagnostic imaging procedures.”

“This is an absolutely sentinel event, a wake-up call,” said Fred Mettler, principle investigator for the study by the NCRP. “Medical exposure now dwarfs that of all other sources.”Reference: With Rise in Radiation Exposure, Experts Urge Caution on Tests NYT, By RONI CARYN RABIN Published: June 19, 2007

Revise the background pie or does more Pb help?

Whose doing our work?

Stanford approaches increasing shielding calculation demands in several ways: Hire one additional health physicist

John Kwofie! Use the manufacturer to do the bulk of the

calculations – then we review and verify Hire a contractor to do the big projects

The new radiation oncology department The new nuclear medicine suite The cyclotron

First Example VA facility new PET/CT machine

Shielded injection and patient waiting room not designed because “patient workload was to be <4 per day.” Workload now 7/day.

Part-time nurse’s dosimeter indicated unusual monthly high exposures (averaging 270 mrem per/month) over 7 months.

Work environment analysis showed the office she’d moved into in August 2006 was next to patient waiting area. When not worn, her lab coat hung on the door facing patient area.

Measured dose rates up to 4 mrem/hr when patients sit near office. 3 months of monitoring waiting area indicates exposures of 300

mrem/month.

Waiting Area

Office

Hot Lab

Our VA Pb recommendations –

The good news: After giving our nurse an EPD we

found that her actual dose (several mrem/day) was far lower than what her badge was exposed to.

The bad news: They now want to put two people into

this small office. Recommendations:

1) Shield the room and convert it into the PET patient injection and waiting area instead of an office.

2) Shield the wall facing the patient waiting room and remove the door.

3) Move PET patients to shielded alcove leading to PET/CT room. (The doctor liked this idea.)

Bottom Line: More Pb

Desk

Desk

Patient

Second Example - The Mobetron The case of the mobile therapy accelerator What is it? A mobile electron beam

accelerator designed for Intraoperative Radiation Therapy (IORT).

Design minimizes radiation leakage and facilitates IORT treatments in non-shielded operating rooms.

When not in use, treatment head locks horizontally, reducing gantry height enabling doorway and elevators access.

Electron beam energies: 4 MeV 6 MeV 9 MeV 12 MeV

Stanford’s Intended Use

The Mobetron weighs 700 lbs. Console and high voltage power supply separate

We will house it in one (maybe two) operating room(s).

The SU Hospital OR room has a storage room with a window. We will permanently set up the console area in that room.

The patient bed needs to be moved and aligned with the Mobetron (this will have it’s own challenges for the nursing staff).

Mobetron shielding considerations

Mobetron gantry rotates +/-45 degrees from the vertical. A beamstopper tracks the rotation and intercepts patient scatter.

Because the Mobetron is mobile, can be used in more than one OR.

Self-shielding limits stray x-ray radiation to <2 mrem at a distance of 3 m from the patient (for a delivered 2000 rad electron beam dose at 50 cm SSD).

Shielding calculation assumptions: 3 patients/week and 150/year QA's to be done in off hours If more studies desired, shorter or lower energy

procedures can be scheduled.

Overhead view of OR room

Mobetron beam side viewNote Angle limitations

Mobetron Calculations:Occupancy assumed to be 1 for adjacent rooms; ¼ for the hallway.

  Annual Dose Annual Dose

Measurement in mrem in mrem

Point no shielding With Occupancy

  added Factor

Passageway North of OR 21.84 5.20

Adjacent OR 87.88 87.88

Work area East of Unit 26.52 6.76

Hallway doors South of unit 38.48 9.36

Hallway South of OR 159.64 40.04

Hallway behind OR 69.68 17.68

Hallway West of OR 121.16 30.16

Hallway West of OR 50.44 12.48

Floor below P-22.5o 192.40 192.40

Floor below P+22.5o 20.80 20.80

Floor below P+45o 0.00 0.00

1 m above floor 8.84 8.84

Mobetron Pb conclusions:

At this time no Pb appears to be required however occupancy information needs to be obtained for the room below the OR.

Administratively limit studies (patients/week and 150/year – or energetically set limits).

Perform QA the night before. Procedures need to be developed for OR

staff that describes Room access limitations Study limitations

Third Example: The Portable CereTom

Intended for x-ray CT applications for anatomy that can be imaged in a 25cm field of view Primarily head and neck

Think: Emergency Department or Oakland Raiders The Raiders now scan players

and diagnose head trauma during games

CereTom information

CereTom is a high resolution 80 KvP 8 row 25cm field of view

Uses dry sealed batteries which power system while unplugged

Has necessary safety features such as Emergency stop switch X-ray indicators Interlocks Patient alignment laser

Has retractable caster wheels so the system can be moved “easily” to different locations.

Stanford’s intended use

To be used by the Lucile Packard Children’s Hospital for: Head scans Infant abdominal scans (Eventually)

Ideal for children too sick to bring to the emergency department. Sick children require tremendous support for

transport (consider IVs, monitors, etc.) The CereTom enables quick decisions and

timely interventions.

CereTom radiation scatter

Dosage linesin mR/sec.

Overallexposurevaries dependingon scan times.

45° angle isareaof highest exposure

CereTom Pb considerations

If the CereTom is rolled into preemie unit what are the exposures to nearby beds? Dose per scan at 1 meter ranges from 1 to 6 mrem

depending on scan parameters Conclusions:

Provide lead curtains or lead impregnated plastic screens that can extend along the side of the bed to shield the 45° angle exposures

Drape nearby incubators with lead aprons Challenges:

Ensure visibility of patient is not hampered Ensure console setup not on 45° angle Ensure administrative controls are practiced

The Tale of Two TrailersFourth Example

Trailers are a packaged unit

Advantage, they come pre-shielded, but shielding must be confirmed by survey.

The GE CT mobile unit has fencing to protect it from vehicles (dose rates outside = background).

PET/CT trailer dose rates are ~ 1 mrem/hr near the injection room and: Has plumbing Combined hot

lab/injection room

Trailer Pb Considerations

Our experience so far has been that these mobile facilities are convenient to use and do not require additional Pb.

Cautions: Park these trailers in areas where there is low

occupancy. Survey exterior to the injection room while

occupied by a patient to ensure dose rates are less than 2 mrem in any one hour.

If dose rates exceed 2 mrem in any one hour consider fencing.

Final Example – VA Room with 3 Cameras Our current project:

Calculate exposure impact to technicians when 3 gamma cameras replaced Hawkeye CTs.

Note control panel and computer work station locations

The VA Camera Room

Control panel areas and works stations are the most vulnerable to radiation from the head of the CT.

Calculations show that control panels areas, if directly behind the CT head will receive 20 mrem/week if technicians stayed in the control panel area throughout the whole study.

Chief Tech’s Office

Current gamma camera locations

Control panels

VA Room with 3 Cameras – Conclusions

The Chief technologist has stated that technicians will not stay in the control panel area. They will move around the room.

Decision: Remove and limit computer work stations behind the CTs. Shift console areas Install portable Pb shields around control panel area.

Control panels

Chief Tech’s Office

Current gamma camera locations

What are the hurdles to good shielding?

Expense

We prefer to design conservatively Use consistent lead

thickness on each wall to minimize errors

Where possible plan for future (assume eventual CT to PET/CT conversions)

Assume patient workload increase.

But Pb is expensive!

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0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

1997 2005 2006 Jul-07

1997

2005

2006

Jul-07

Dollars/pound per year

What’s up with Pb?

By Jan. 6 of this year, Money Week reported that lead prices were up 40 percent for the year (!!).

Market conditions are driven by China. The Chinese, (leading exporters of lead) have: Decreased their exports Added a 10 percent tax on lead Now use more lead in their own manufacturing

processes. The US has five lead mines in: Missouri, Alaska,

Idaho, Montana, and Washington.

What manufacturing processes are we competing with? Automobile/truck lead-acid battery industry are

the principal users of lead (83%). 11% of lead used in ammunition; casting

material; sheets (including radiation shielding), pipes, cable covering, solder, and oxides for glass, ceramics, pigments, and chemicals.

The balance used for uninterruptible power-supply equipment for computer and telecommunications networks and hospitals, and, ballast and counter weights!

What are other hurdles?

Time They may have end of year money to use or a

company may be donating a machine and a “hot” offer may cool off.

Get comfortable with and use that spreadsheet. Space

Retrofitting rooms and replacing older less energetic machines with newer more energetic machines:

A simulator room becomes a PET/CT room Find out what Pb may already exist in the walls

(This may also be a challenge).

To Conclude …

Is More Pb the Answer in a Changing Medical

Environment?

At Stanford we found that for:

PET patients and PET/CTs the answer is always yes.

Portable units like the Mobetron, CereTom

administrative controls can work.

Trailers – no – but survey to confirm

Machine replacements into existing rooms – usually,

but:

The more space the better

Look at existing Pb and determine if it is adequate

Thank you!

Questions?