2001 AAPM Summer School Seattle, Washington ACR R/F Phantom

Transcription

1 2001 AAPM Summer School Seattle, Washington ACR R/F Phantom Charles R. Wilson, Ph.D., FACR Medical College of Wisconsin Milwaukee, Wisconsin

2 MCMC Circa 1975

3 ACR R/F Phantom This lecture has been approved for 1 hour of continuing medical physics education credits by CAMPEC. This lecture also has pending FDA approval for the treatment of a common condition affecting many individuals in the US. This condition will be named for those still awake at the end of this talk. INSOMNIA!

4 R/F Physics Subcommittee Name - Robert Dixon - Beth Schueler - Charles Wilson - Pam Wilcox - Penny Butler - Krista Bush - Call Name Captain Midnight Wonder Woman Obiwon Kenobi Xena Warrior Princess Goldilocks Buffy the Vampire Slayer

5 Prototype Chest Accreditation Phantom AnteriorResting Portion Full Phantom in Peace

6 R/F Phantom Design Criteria Radiographically tissue equivalent PMMA and aluminum weight: 12 to 30 pounds Build on existing, widely used phantoms CDRH chest and abdomen NEXT phantoms Modular design chest, abdomen and interventional programs Inexpensive and easy to interpret

7 CDRH NEXT Abdomen Phantom ACR Barium Enema Quality Control Manual

8 CDRH Chest Phantom

9 ACR R/F Phantom Components Test object plate (1 cm PMMA) 2. Aluminum plate (3/16 ) 3. PMMA block (7.6 cm) 4. PMMA block (7.6 cm) 5. PMMA block (4.1 cm)

10 7.6 cm ACR Chest Phantom Chest (horizontal tube) Air gap

11 ACR Abdomen Phantom Abdomen (overtable tube) 7.6 cm 7.6 cm 4.1 cm

12 ACR R/F Test Objects A. Contrast Detail Pattern 4 rows 6 columns B. Copper mesh 9 patterns C. Central aluminum disk 9 low contrast objects D. Aluminum disk Latitude test A B D C

13 Phantom Image Evaluation Suggested Criteria (1) High Contrast Mesh Chest 8 or better Abdomen 7 or better Spot film 5 or better Central Aluminum Disk Chest 7 or better Abdomen 7 or better Spot film 6 or better

14 Phantom Image Evaluation Suggested Criteria (2) Contrast Detail Columns from left 4 / 4 / 3 / 2 Optical Density Chest 1.3 to 1.6 Abdomen 1.3 to 1.6 Spot film 1.0 to 1.8 Latitude Disk To be established

15 Contrast Detail Test Object Contrast Subject (~%) Diameter 5.6 mm 4.0 mm 2.8 mm 2.0 mm Suggested performance standard : All objects to the left of the dotted line are to be visible.

16 Phantom Transmission Test Geometries Narrow Beam Wide Beam

17 Narrow Beam % Transmission CDRH and ACR Chest Phantoms 14 Percent Transmisison Lucal Phantom ACR Phantom kvp ACR ~ 2.5 cm more PMMA

18 Scatter to Primary Ratio CDRH and ACR Chest Phantoms ACR Phantom 1.5 S/P CDRH Phantom kvp

19 Wide Beam % Transmission CDRH and ACR Chest Phantoms 30 Percent Transmission CDRH Phantom ACR Phantom kvp ACR: Air gap ~ 9 cm less

20 Technique Factors (GE DR unit at 120 kvp) ACR Chest Phantom 2.5 mas (0.126 mgy) CDRH Chest Phantom 2.04 mas (0.103 mgy)

21 Technique Factor Comparison (GE DR unit at 120 kvp) ACR Chest Phantom 2.5 mas (0.126 mgy) 16 consecutive male patients Averages: 201 lbs, 3.2 mas, 0.16 mgy 18 consecutive female patients Averages: 173 lbs, 2.5 mas, mgy mas Weight ACR Chest Phantom equivalent to ~ 170 lb man or woman

22 CDRH and ACR Abdomen Phantoms ( Total Acrylic = 19.3 cm 4.1 cm 7.6 cm 4.6 mm Al 7.6 cm Air gap Test object plate (3/8 in thick)

23 Narrow Beam % Transmission CDRH and ACR Abdomen Phantoms Percent Transmission CDRH Phantom ACR Phantom kvp

24 Entrance Skin Air Kerma Dosimeter Desirable Characteristics Precise Energy independent response Linear response with air kerma Accurate Choices Thermoluminescent Dosimeter (TLD) Optical Stimulated Luminescence (OSL)

25 Luxel Personnel Dosimeter

26 Preliminary Tests of Luxel Personnel Dosimeter Energy response Dosimeter pairs irradiated using different hvl beams 0.32, 0.67, 2.2, 4.2, 5.1 and 6.0 (mm Al) 1.5 Dosimeter Response HVL (mm Al) Exposure response linear from 4 to 900 mr Precision acceptable: ~ 10 mr > 100 mr

27 Optical Stimulated Luminescence OSL Illuminate an irradiated crystal (Al 2 O 3 ) with a given wavelength of light to initiate the movement of charge from trap sites to luminescence centers. Amount of luminescence is proportion to dose and amount of illumination (optical energy) imparted to the crystal.

28 Conceptual Energy Diagram Following Irradiation X-Rays C o n d u c t i o n B a n d Electrons Unpopulated Shallow Traps Populated Dosimetric and Deep Traps Luminescence Center V a l e n c e B a n d

29 Conceptual Energy Diagram Delayed and Pulsed OSL Stimulation C o n d u c t i o n B a n d Stimulation Light Retrapping in Metastable Shallow Trap Luminescence Center V a l e n c e B a n d Partial Depopulation of Dosimetric and Deep Traps

30 Luxel Dosimeter with Filter

31 Dosimeter on Test Tool

32 Luxel Dosimeter Response Chest kvp 1000 Given Air Kerma (mrad) y = x R 2 = Given Air Kerma (mrad) Observed Linear Luxel Reading (mrad) Luxel Reading (mrad)

33 Luxel Accuracy vs Given Air Kerma Chest 120 kvp % Deviation RMS Deviation=13.2% Log (Air Kerma mrad)

34 Given Air Kerma vs Luxel Reading Chest Phantom 1000 Given Air Kerma (mrad) kvp 120 kvp 140 kvp Luxel Reading (mrad)

35 Luxel Dosimeter Response Abdomen kvp 1200 Given Air Kerma (mrad) y = x R 2 = Luxel Reading (mrad)

36 Dosimeter Precision Two sets of 6 dosimeters were irradiated using 100 and 120 kvp beams. Dosimeters on top of phantom. 100 kvp (6): /- 2.6 mrad ( 3.2 %) 120 kvp (6): /- 1.5 mrad ( 4.2%) Pairs of dosimeters were irradiated at air kermas of ~ 9, 36, 90, 360 and 900 mgy using 80 and 120 kvp beams. RMS Differences 80 kvp (5 pairs): 3.5% 120 kvp (5 pairs): 2.0%

37 Selection of Phantom Manufacturer RFP sent to potential manufacturers RFP contained detailed specifications Materials Phantom and test object dimensions and tolerances i.e. hole depth for low contrast object: / Manufacturers submitted three phantoms for testing

38 Manufacturers Response to RFP

39 Selection of Phantom Manufacturer Phantoms evaluated by an independent medical physicist IMP chosen on basis of qualifications Availability of appropriate test equipment Quality of IMP evaluation of three prototype phantoms constructed by ACR Committee s choice of manufacture based on IMP s tests of the manufacturer s pre-production phantoms

40 Average Difference (Specified Actual) Hole Depths in Central Aluminum Disk Specified) p ) p ) Manufacturer X SD AVE = Manufacturer Y SD AVE = Manufacturer Z SD AVE =

41 Pilot Accreditation Program Initial Phantom Data 9 facilities participated in pilot accreditation program Low Contrast Detail Objects Entrance Air Kerma

42 Contrast Detail Evolution Chest Phantom 3 physicists somewhat independently scored images Excellent agreement for 7 of 9 films 6 passed and 1 failed 2 disagreements

43 5 Entrance Skin Exposures Pilot Program 4 3 Chest ESE < 50 mr Abdomen ESE < 1000 mr ESE (mr)

44 Initial Experience With Abdomen Phantom Incorporated phantom into annual equipment checks Data collection form is an Excel spreadsheet Automatically performs linear regression of kvp vs mr/mas Computes ESE for abdomen and chest phantoms from kvp and mas used Outliers are easily seen Optical Density Abdomen OD vs ESE Entrance Skin Exposure

45 All things come to an end. Thank you.