Routine compliance inspections of dental panoramic x-ray units in use within the Commonwealth of Pennsylvania have, over the years, revealed inconsistencies in patient dose and image quality.

In an attempt to address these inconsistencies, a detailed survey was developed that included making radiographs of a skull phantom, measuring x-ray exposure, and gathering information on x-ray and processing technique. The 121 surveyed facilities were chosen at random from a database of 1000+ registered facilities operating panoramic units in the western 22 counties of Pennsylvania.

The survey was conducted under the auspices of Pennsylvania's newly created Pollution Prevention Initiative. This program, through the Department's staff, encourages Commonwealth businesses to investigate available technologies and voluntarily attempt to minimize pollution while producing products of the highest quality. The Bureau of Radiation Protection views unnecessary radiation exposure as a pollutant and, in this realm, the radiograph as the product. The objective of the panoramic study was to reduce patient and operator radiation exposure by correcting errors in technique, optimizing the film/intensifying screen combination, and/or identifying darkroom deficiencies. After all of the measurements were completed, the physician was given the opportunity to review the resultant radiographs and rank them by preference. Once a preferred image was established, the surveyors explained the steps necessary to obtain this image to the facility representatives.

 

EQUIPMENT

The kit includes: a skull phantom, the Capintec model 192 electrometer with the PM-05 and PC-4P ion chambers, laptop computer, sensitometer and densitometer, a box of Kodak XRP-5 x-ray film, digital thermometer, 2.5 millimeters of aluminum, tripod, and Kodak* beam filter kits, Lanex Regular intensifying screens for each type of panoramic system, and T-Mat G x-ray film.

The phantom is a human skull and cervical spine encased in tissue-equivalent material. A steel sphere was placed between the molars on each side to monitor our ability to position the phantom properly. Resolution meshes of 24, 50, 60, 80, and 100 lines per inch were positioned in the gap between the upper and lower incisors. Two chamber ports, one in the center of the oral cavity and one at the thyroid, were made to accommodate the PM-05 ion chamber.

*Our gratitude goes out to the Eastman Kodak Company for recognizing what we were trying to accomplish and for providing the film, screens, and beam filter kits. Their assistance and expertise were an integral part of the survey.

PROTOCOL

At each facility, we secured the phantom to the tripod and positioned it as best as possible using the facility's positioning technique. Exceptions had to be made at times with certain models of units primarily due to limitations of the phantom. The phantom's neck and ears were unforgiving, leading to an occasional positioning technique that differed from what would be used clinically, but this was explained to the facility operator when appropriate. The PM-05 ion chamber was inserted into the mouth chamber port and the facility operator was asked to set the technique factors for a male of approximately 20 years of age.

The first radiograph was produced using the facility's current film/screen combination and its x-ray and processing techniques. This film was routinely shown to the technician or doctor prior to proceeding. If the image was not an example of what they normally see, adjustments, as necessary, were made in positioning, etc., and the exposure was repeated until a comparable image was obtained. Directly after producing a panograph indicative of what the facility agreed was typical, a sheet of the XRP-5 film was exposed with the sensitometer, then processed and evaluated.

At the surveyor's discretion, a second film with the facility's current setup was produced with a beam filter taped over the tube slit. This step was eliminated if the surveyor felt this image would be too light, based on the optical density of the initial film. This film was more often produced at facilities that were already using a 400 speed film/screen combination.

After the Sensitometric Technique for the Evaluation of Processing, or STEP, film was processed, we made whatever changes possible, short of changing the developer and fixer, to optimize the system. This may have included correcting errors in processing technique, patient positioning, x-ray technique factors, and upgrading the film/screen combination to 400 speed. As many films as necessary were produced with varying technique factors and/or one or more beam filters until we felt we had an optimal image of the skull phantom. The beam filters were taped directly over the slit on the beam-limiting device. An optical density was recorded at a designated location just behind the back molars on each panograph produced.

Before the phantom assembly was dismantled radiation measurements were recorded at both chamber port positions for each technique resulting in a film retained for the exit meeting. The PC-4P chamber was then connected to the electrometer and taped along the tube side of the slit at the image receptor. With nothing in the radiation beam, measurements were again recorded using each of the techniques that corresponded with one of the films we intended to use during the exit meeting. These in-air measurements might be used to back calculate an exposure at a possible iso-center with any prescribed theory.

The last exposure recorded was with the x-ray unit set at the original technique, but with 2.5 millimeters of aluminum taped to the beam limiting device. Due to long tube cooling times and availability, every effort was made to keep the number of exposures taken on a given panoramic system to a minimum, thus, only two measurements (0.0 mm and 2.5 mm added) were recorded for an approximate half value layer determination. We initially intended to measure the kVp on each system, but this step was also eliminated in order to minimize the number of exposures.

At the exit meeting with the doctor, we explained the results of the STEP evaluation and asked him/her to review the radiographs produced and rank them by preference. There was always a minimum of two images to choose from, and often three or four. Information such as differences in the radiation exposure necessary to produce the radiograph and the cost involved in making an upgrade in film/screen combination was normally not revealed until after the doctor completed his/her evaluation. We then described the adjustments and/or equipment necessary to obtain the image the doctor preferred. The survey often required two or more hours to complete and we made every attempt to accommodate the office's schedule and minimize the disruption of patient care.

The facility subsequently received a letter summarizing the results of the thyroid port measurements and an indication of the preferred image. Changes necessary to obtain the preferred film were not specifically outlined in the letter. As any decision to change from their current protocol was entirely up to the facility, we developed a system to record any changes resulting from the survey during the next routine compliance inspection. Since Pennsylvania inspects dental facilities routinely on a four-year cycle, the results of this part of the survey will not be available for at least four years.


FINDINGS

Twenty-four different models of panoramic systems, ranging in age from only several months to over 22 years, made up the 121 facilities surveyed. See Table 1. The number of panographic films taken per month ranged from three to 150, resulting in an average of 28 films per facility or an estimated 3300 total films each month.

Table 1. Panoramic systems

Type Number of Facilities Age Films Per Month Oldest Avg. Newest Min. Avg. Max.
SS White Panorex

21

1975

1978

1987

5

30

150

Ritter Panoral

22

`78

`80

`90

4

30

130

GE Panelipse

16

`75

`77

`80

7

32

75

Panoramic PC 1000

9

`90

`93

`96

10

31

100

Gendex GX Pan

7

`93

`94

`96

5

11

25

Planmeca PM 2002 CC

5

`88

`91

`96

10

30

75

Sybron Panoral

6

`79

`84

`86

5

21

60

Morita Versaview

4

`87

`90

`92

8

35

80

Belmont 98

4

`86

`88

`89

15

19

25

SS White Panorex 2

7

`83

`84

`85

3

16

60

GE Panelipse

3

`76

`84

`88

12

47

100

Siemens Nanodor 2P

3

`75

`76

`77

5

9

15

Siemens Orthopano 10

2

`84

`84

`84

10

25

40

Belmont 098 E

2

`85

`86

`87

25

48

70

Philips Oralix Pan DCII

1

`90

15

Siemens Orthopan 3

1

`95

30

Sordex Cranex 2.5+

1

`94

15

Panoura 10SU

1

`93

5

Instrumentarium OP 100

1

`97

20

Gendex Ortho SD 2

1

`96

50

Morita Panex

1

`77

15

Fiad Rotograph 230

1

`87

10

Siemens Orthopan

1

`96

100

Gendex Panelipse II

1

`96

5

Twenty-seven facilities processed their films manually and 14 different models of automatic processors were found at the remaining 94 facilities. See Table 2. The facilities using dip tanks faired considerably better in processing efficiency with an average speed of 94 percent compared to only 60 percent for the automatic processors. Most facilities reported changing their chemistry at least monthly. See Figure 1 (located below Table 2).


Table 2. Film processing

Type # of Facilities STEP Temperature ° F Time (min.) Min Avg Max Min Avg Max Min Avg Max
Manual

27

18

94

178

62

73

91

0.5

4

10

Air Tech 2000

33

12

53

105

66

81

86

4

5.1

7

Air Tech 2000+

15

10

57

95

66

80

85

4

4.6

5.5

Philips 810

19

22

62

205

70

80

94

3

4.2

5.5

Dentx 810 Basic

9

30

62

90

81

84

88

4

4.6

6

Philips 810 XL

4

28

68

115

78

83

87

1.5

3.8

4.5

Gendex GXP

4

42

69

117

81

83

86

4.5

4.8

5.5

Dentx 810

3

20

53

111

70

79

84

3.5

4.2

4.5

Fischer

1

112

86

4

Philips 810 Basic

1

88

84

4.5

Dentx 8 DE

1

32

78

4.5

Litton

1

29

73

4.5

Konica

1

115

96

4

Air Tech All Pro

1

37

78

3.5

All Pro ER

1

53

67

4.5

Figure 1. Chemistry change frequency


Half (60) of the surveyed facilities used a 200 speed film/intensifying screen combination, while 50 sites had 400 speed and one used an 800 speed combination. Ten facilities were found to have inappropriately matched film/screen combinations. Ninety percent (109 facilities) stated that they do not clean their intensifying screens routinely. See Table 3.

Table 3. Intensifying screen maintenance

Intensifying Screen Cleaning Frequency Weekly 2 weeks Monthly Quarterly Never Number of Facilities
1 2 7 1 109

Ninety-four, or 78%, of the doctors preferred a phantom image produced with less radiation exposure than what they typically used. The majority of these chose the "optimal" image outright. If the doctor stated that it was a "toss up," he/she often sided with the film that was produced with less radiation after we explained our technique for each radiograph, and these are included in the 78%. As surveyors, we stressed that an optimal image took precedence over dose and avoided detailed discussions with the doctor regarding the number of "rads" saved. We preferred to speak in terms of the percent decrease in widgets. See Table 4.

Table 4. Summary of the radiation exposure reduction at facilities
choosing an image with lower dose

Type # of Facilities Percent Reduction to Thyroid Port # of Facilities Selecting Own Image Min. Avg. Max.
200 Speed

52 *

24

52

73

7

400 Speed

34**

12

35

68

15

Mismatches

8

30

47

73

2

Total

94

12

46

73

25

* One additional doctor was unable to evaluate the films.
** One additional facility had a 17% increase in radiation exposure.

Seven of the 60 facilities using a 200 speed film/screen combination selected their own image. The dentist at one facility did not have the opportunity to review the radiographs. The average reduction in radiation exposure was 52% (minimum 24%, maximum 73%) at the 52 offices choosing an image other than their own. The overall average optical density of the panographs increased from 1.07 to 1.28 when comparing the facility's current film with the preferred film. In addition to upgrading to a 400 speed combination, each of the 52 units required one or more of the changes outlined in Table 6.

Fifteen of the 50 facilities using a 400 speed film/screen combination selected their own image. One doctor chose an image obtained with a 17% increase in radiation exposure. The average reduction in exposure at the other 34 offices choosing an image other than their own was 35% (minimum 12%, maximum 68%). The overall average optical density of the panographs at facilities already using a 400 speed combination dropped from 1.43 on the current films to 1.10 on the preferred films. The changes required to obtain the preferred image at these 35 facilities are outlined in Table 6.

Two of the 10 facilities using an inappropriate combination of film and intensifying screen chose their own film. The average reduction in exposure at the remaining eight offices was 47% (minimum 30%, maximum 73%). The average optical density of the panographs increased from 0.94 on the original films to 0.99 on the preferred films.

Overall, 94 of the 121 facilities surveyed chose a panograph created with less radiation exposure over an image they categorized as typical. If every facility adopted the technique used to create the preferred film, radiation exposure would drop by an average of 40% across the surveyed facilities, and the average optical density would be maintained (1.21 for the original or current film versus 1.18 for the preferred film). See Table 5.

Table 5. Summary of changes in the optical density

Reduction in Radiation Exposure Resulting Images Optical Density 200 Speed 400 Speed Mismatches All Facilities Average Minimum Maximum
Original 1.07 1.43 0.94 1.21
Preferred 1.28 1.10 0.99 1.18
Original 0.49 0.40 0.32
Preferred 0.57 0.33 0.55
Original 2.38 2.45 1.36
Preferred 2.38 2.45 1.53

Table 6. Summary of technique changes applied to create preferred images

Selection Number of
Facilities Number of Filters kVp MA 1 2
200 Speed 60 22 15 19 17
400 Speed 50 31 1 3 1
800 Speed 1 0 0 0 0
Mismatches 10 1 2 4 1
All Facilities 121 58 18 26 19

As already stated, due to the multiple difficulties in calculating a patient's actual dose from the survey technique used, we chose to address the results in terms of widgets saved during the exit meeting with the doctor. A summary of our radiation measurements is included in Table 7 for informational purposes only. Any derived estimate of patient dose is not necessarily that of the authors. It is notable, however, to point out that, if all facilities adopted the technique of the preferred film, the dose distribution is substantially narrower.


Table 7. Summary of radiation exposure measurements

Chamber Location Resulting Images Minimum milliRoentgen Average milliRoentgen Maximum milliRoentgen
Mouth Port Current 7 34 106
Preferred 6 22 105
Thyroid Port Current 21 85 250
Preferred 16 50 170
Slit Current 1560 5505 15520
Preferred 720 2975 11840

The results of the half value layer estimation are outlined in Table 8. Radiation measurements at the image receptor slit, including the half-value layer determination, could not be collected on some models due to insufficient clearance for the PC-4P ion chamber. Follow-up visits are expected at the units that did not pass the regulatory standard.

Table 8. Summary of half-value layer

Indicated kVp Range Number of Facilities mmAl Minimum Average Maximum
60 69 11 1.87 2.74 4.86
70 79 27 1.64 2.97 6.12
80 89 54 1.82 2.95 6.82
90 99 17 1.94 2.87 3.61
100 above 4 2.43 3.18 3.81

CONCLUSIONS

During the course of the survey it became apparent that many facilities accepted an image that was less than optimal. Facilities require varying degrees of quality depending on intended use of the film. This became obvious after seeing their enthusiasm when they realized the image quality their system was capable of producing after a minor upgrade and/or technique change. This enthusiasm struck our target goal of improving image quality while reducing unnecessary radiation exposure.

The images produced with the skull phantom were an essential part of the survey. State inspectors have preached during routine inspections the advantages of upgrading outdated film/intensifying screen combinations for years, but an image coinciding with patient dose comparisons is a very effective method. The cost of a new intensifying screen capable of 400 speed or greater is about $200. This was inconsequential to most facilities, especially when the appropriate film was cheaper than the film they were currently using.

In our opinion, the survey produced a better panograph with less radiation exposure at all of the facilities that were using a 200 speed or mismatched film/screen combination. Many doctors were surprised that their older unit was capable of producing such quality. Yet, it appeared some facilities chose their current image over what seemed to be a much better image as if choosing another would lead to an obligation to change. The survey data supports the fact that the age of the x-ray machine was inconsequential to image quality or patient dose.

The number of facilities already using 400 speed that preferred the image with the beam filter was unexpected. We hope our effort to convey that image quality, not dose reduction, was our primary concern did not go unrecognized. The filter was shown to reduce radiation exposure by about 35% while only hardening the x-ray beam by approximately 0.5 millimeters aluminum equivalent. As mentioned, many doctors liked the idea of reducing patient "dose" by 35% and felt image quality was maintained or improved.

The survey revealed problems with patient positioning and technique that would normally go undetected during a routine compliance inspection. A state inspection often is the only critique of the diagnostic imaging process in dental offices. A simple review of the facility's radiographs would be beneficial in revealing potential positioning and/or technique problems. Therefore, it is important for state inspectors to be knowledgeable in the operation of these unique systems, as well as in the image these systems produce.

Several problems in processor quality control and technique that substantially affected the image quality or patient dose were noted. For example, we encountered a facility that ran panographic films on the endo time setting. This was brought to the facility's attention during the exit meeting. The low average efficiency of the automatic processors was certainly disturbing. See Figure 2. Even processors operating as designed with regard to time, temperature, and fresh chemistry did not achieve high efficiency. Most facilities reportedly followed the manufacturer's recommended maintenance schedule, but many still did not place enough emphasis on the importance of quality control in the darkroom and processing.

A pre-designed system to track the effectiveness of the survey was established. The success of the survey to maintain or improve image quality while reducing radiation dose will be determined after the next routine state inspection is completed at each facility. We believe that the program made a considerable impact at the 121 facilities visited and should be continued. The number of offices visited represents only about 4% of the estimated 3000 producing panographs in the Commonwealth. Assuming all facilities average 28 films per month, a substantial improvement in image quality while reducing patient exposure (Figure 3) by an overall average of 40% would be significant.

THE PENNSYLVANIA DENTAL PANORAMIC X-RAY STUDY

Performed by:
John P. Winston & Dwight A. Shearer
Pennsylvania Department of Environmental Protection
Radiation Protection Field Operations
Pittsburgh, Pennsylvania

Notice: The above article does not represent an agreed-upon staff position of the Pennsylvania Department of Environmental Protection, nor has this agency approved the technical content. Mention or depiction of any instrument or other equipment is for illustration only, and does not constitute any endorsement of that product.

 

 

 

 

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