Fluke 660-6 User Manual

Download

Victoreen®

660-6

500-100

6000-100

660-7 & 660-8

CT Probes and Phantoms

Operators Manual

Fluke Biomedical

Radiation Management Services

6045 Cochran Road Cleveland, Ohio 44139

440.498.2564

www.flukebiomedical.com/rms

Table of Contents

Section 1: Introduction................................................................................................ 1-1

1.1 Product Description ..................................................................................... 1-1

1.2 Specifications............................................................................................... 1-1

1.2.1 CT Probes .............................................................................................. 1-1

1.2.2 Phantoms ............................................................................................... 1-5

1.3 Receiving Inspection.................................................................................... 1-5

1.4 Storage ........................................................................................................ 1-5

Section 2: Theory of Operation................................................................................... 2-1

2.1 Theory of Operation..................................................................................... 2-1

Section 3: Operation.................................................................................................... 3-1

3.1 Operation ..................................................................................................... 3-1

Section 4: Probe Calibration....................................................................................... 4-1

4.1 Probe Calibration ......................................................................................... 4-1

Appendix A: Radiation Dosimetry in Computed Tomography .................................... A-1

A.1 Radiation Dosimetry in Computed Tomography .......................................... A-1

(Blank page)

Introduction

Product Description

Section 1

Introduction

1.1 Product Description

CT Probes, Models 660-6, 500-100, and 6000-100 are designed to be used with Phantoms, Models 6607 and 660-8, to measure exposure produced by Computed Tomography (CT) Scanners.

The probes (Figure 1-1) consist of a pencil type ionization chamber with a sensitive length of 10.0 cm. The Model 660-6 probe chamber is connected, via 0.9 m (3 ft.) of low noise flexible cable, to a signal digitizing pre-amplifier. It is designed to be readout on a Model 660 Digital Exposure Meter. The Model 500-100 probe chamber is connected to 0.9 m (3 ft.) of low noise flexible cable terminated with a male BNC size triaxial connector. It is designed to be readout on a quality electrometer. Model 600-100 (notshown) is similar to the Model 500-100, but designed for the NERO™

The phantoms (Figure 1-2) are designed in accordance with the definition in the FDA Center for Devices and Radiological Health, performance standard 1020.33 Computed Tomography (CT) equipment, “NCT Dosimetry Phantom”. Model 660-7 is a body phantom; Model 660-8 is a head phantom.

1.2 Specifications

1.2.1 CT Probes

Detector Type

Volume

Sensitive Length

Chamber Material: Clear Acrylic

Electrode Material: Aluminum

Sensitivity

Factory Calibration

Energy Response

Beam Orientation

Phantom Adapter Outside Diameter: 1.27 ± 0.04 cm (0.50 ± 0.015 in)

Model 66O-6 (with Model 660 Readout)

Vented air ionization chamber

3.2 cc

10.0 cm

Inside Diameter: 6.4 mm

Wall Thickness: 54 mg/cm

Diameter: 0.64 mm

10 R cm/nC (nominal)

100 KVCP, 5.5 mm Al hvl

+5%, 1 mm Al to 10 mm Al hvl (see Figure 1-3)

Uniformity (along axis): + 3% over central 90% of active length (see Figure 1-4)

Normal to chamber axis

Maximum Display: 999 R cm/min, 99.9 R cm

Maximum Resolution: 0.01 R cm/min, 0.001 R cm

1-1

Victoreen 660-6,660-7,660-8,500-100,6000-100

Operators Manual

Figure 1-1. Model 660-6 and Model 500-100 CT Probes

1-2

Figure 1-2. Model 660-7 and Model 660-8 Phantoms

Introduction

Specifications

Figure 1-3. CT Probe Energy Response (Phantom Adapter Removed)

1-3

Victoreen 660-6,660-7,660-8,500-100,6000-100

Operators Manual

Figure 1-4. CT Probe Unit Length Response

Model 660-6 (Cont’d)

Intensity Limits: Continuous Beam:

985 R/min (1% recombination loss, ion chamber) 1080 R cm/min (electronic preamp limitation)

Pulsed Beam: 1.6 mR/pulse (1% recombination loss)

Maximum Pulse Repetition Rate: 700 Hz

Ion Transit Time: 1.3 ms

Model 500-100 (with 300 Volt Collection Potential)

Leakage Current: 10 min polarization time: <10

2 hr polarization time: <10

Intensity Limits: Continuous Beam: 4.86 kR/min (1% recombination loss) Pulsed Beam: 51.5 mR/pulse (1% recombination loss)

Maximum Pulse Repetition Rate: 3.3 kHz

Ion Transit Time: 0.3 ms

Connector: BNC triaxial

-14

-13

1-4

Introduction

Specifications

1.2.2 Phantoms

Material

Thickness Diameter

Probe Holes

Volume

Acrylic Plastic

15 cm

Model 660-7 Body Phantom: 32 cm (12.60 in)

Model 660-6 Head Phantom: 16 cm (6.30 in)

Arrangement: One on center, four around periphery (90

degrees apart, 1 cm in from edge)

Inside Diameter: 1.27 cm

3.2 cc

1.3 Receiving Inspection

Upon receipt of the unit:

1. Inspect the carton(s) and contents for damage. If damage is evident, file a claim with the carrier and notify Fluke Biomedical, Radiation Management Service at 440.248.9300.

2. Remove the contents from the packing material.

3. Verify that all items listed on the packing list have been received and are in good condition.

If any of the listed items are missing or damaged, notify Fluke Biomedical.

NOTE

1.4 Storage

If the unit is to be stored prior to use, pack it in the original container(s), if possible, and store in an environment free of corrosive materials, fluctuations in temperature and humidity, and vibration and shock.

The equipment described in this manual is intended to be used for the detection and measurement of ionizing radiation. It should be used only by persons who have been trained in the proper interpretation of its readings and the appropriate safety procedures to be followed in the presence of radiation.

Although the equipment described in this manual is designed and manufactured in compliance with all applicable safety standards, certain hazards are inherent in the use of electronic and radiometric equipment.

CAUTION

1-5

Victoreen 660-6,660-7,660-8,500-100,6000-100

Operators Manual

(Blank Page)

Theory of Operation

Section 2

Theory of Operation

2.1 Theory of Operation

In a phantom, integration of the radiation exposure profile produced by a single scan from a CT scanner along a line normal to the slice, divided by the table increment, is equal to the average exposure produced by a series of scans to a central slice at that point. * The line of integration must be of sufficient length to intercept both the primary beam and the Compton scanner produced in the phantom. The integral is expressed as R cm.

A long, thin radiation probe can be used for the measurement. The probe should be calibrated in a uniform field covering its entire sensitive length, with a correction factor determined in the conventional manner. Subsequent probe readings, multiplied by the correction factor and then by its sensitive length, will be in units of R cm.

The CT probes are designed especially for CT scanner applications. The correction factor due to their length (10.0 cm) is built into the probe calibration:

• The Model 660-6, when used with the Model 660, is read directly in R cm or R cm/min.

• The Model 550-100 correction factor is stated in R cm/coulomb

NOTE

In applications where the probes are used to measure uniform field exposure in terms of R, the Model 660 readings should be divided by 10 or the Model 500-100 correction should be divided by 10.

*R. A. Jucius, G. X. Kambic, “Measurements of Computed Tomography X-Ray Fields Utilizing the Partial Volume Effect”

2-1

Victoreen 660-6,660-7,660-8,500-100,6000-100

Operators Manual

(Blank Page)

Operation

Section 3

Operation

3.1 Operation

The following considerations should be noted when using CT Probes and Phantoms:

• The phantom adaptor (built-up sleeve) is designed to provide mechanical protection for the ion

chamber and to properly place the probe’s sensitive volume in the phantom.

• The phantom adaptor should never be removed from the probe in the field; it should only be

removed when necessary and in the calibration laboratory (e.g., to verify probe sensitivity).

• The hole plugs supplied with the phantoms have small 1.5 mm holes through their midpoint. When

the phantom is properly centered in the CT beam, the holes will appear as small rectangles on the CT scan.

• The ion chamber electrode is not guarded; therefore, after a collection voltage is applied, allow five

minutes for the insulators to polarize.

• If using the Model 660 readout, five minutes after the unit is turned on remove the plug button in the

probe preamp and adjust the zero (while in the Rate Mode).

The Model 660 does not read below zero; therefore, adjust the zero from a positive reading down to just zero. Otherwise, appreciable error may be introduced due to negative leakage.

Use the above guidelines and following procedure to take data

CAUTION

1. Position the phantom, readout device, and cable.

2. Connect the probe to the readout device.

3. Turn on the readout device, applying a collection voltage.

4. Run a scan to check that the holes in the hole plugs are visible.

5. Place the probe in the phantom.

6. Place the probe readout in the integrate mode.

7. Wait one minute to be sure there is not excessive leakage.

8. Run scans and record data as required.

3-1

Victoreen 660-6,660-7,660-8,500-100,6000-100

Operators Manual

(Blank Page)

Probe Calibration

Section 4

Probe Calibration

4.1 Probe Calibration

The Models 660-6 and 500-100 probes are factory calibrated with the correction factor built into the calibration. However, since the NERO™ electrometer is calibrated with the internal ion chamber, it is impossible to supply a CT probe correction factor that applies to all NEROs. Therefore, the user must calibrate the probe with the NERO it is to be used with. Use the following procedure:

Calibration should be performed on a standard radiographic x-ray machine rather than a CT machine.

1. Set the x-ray machine to 100 kVp, 300 mA, and 0.5 sec.

2. Place the probe on the table:

• The source to detector distance (SDD) should be 40 inches.

• The equilibrium sleeve should be in place.

• The probe should be perpendicular to the tube axis to minimize the heel effect.

3. Collimate the beam so that it uniformly irradiates the entire length of the probe.

4. Attach the probe to the NERO detector:

a. Connect the BNC connector to the appropriate jack on the side of the NERO

b. Plug the banana plug into its mating jack.

5. Position, and if necessary shield, the NERO detector so that radiation does not fall on the ion

chamber.

6. Use the detector cable to plug the detector into the NERO unit, plug the unit into AC power, and

turn it on.

7. Verify the mR correction factor by pressing the key sequence F mR on the NERO. The correction factor should be displayed on the LCD.

If 1.000 is not displayed, enter 1 and press ENT.

8. Set the NERO up for an exposure by pressing the key sequence F 5. Observe the following:

• The display will clear as NERO measures electrometer drift for twelve seconds.

• The NERO will then beep and display 0.0 mR.

9. Make an exposure and record the results.

10. Press NEXT to clear the display.

11. Repeat Steps 9 and10 to obtain a total of five exposures.

NOTE

4-1

Victoreen 660-6,660-7,660-8,500-100,6000-100

Operators Manual

NOTE

All five exposures should be within 3%.

12. Compute an average of the five exposures. Record the average as the Measured Value.

13. Press EXIT to return the NERO to the Ready condition.

14. Remove and disconnect the CT probe.

15. Place the NERO detector in the center of the beam.

16. Raise the tube 2.25 inches to compensate for the height of the detector box.

17. Make an exposure and record the results.

18. Press NEXT to clear the display.

19. Repeat Steps 17 and 18 to obtain a total of five exposures.

NOTE

All five exposures should be within 3%.

20. Compute an average of the five exposures. Record the average as the True Value.

21. Compute the correction factor for the probe as follows:

cf = 1 x True Value/Measured Value where 1 = the probe length (10 cm).

22. Record the correction factor.

Use the computed correction factor when making CT dose measurements. Enter it into the NERO as the mR correction factor (by pressing F mR, entering the factor, and pressing ENT). The display will then read directly in mR cm.

4-2