First step of quality controls has involved the test of linearity of the radiation dose as a function of mA and and the repeatability of the voltages and the times.
The linearity of the dose has been measured directly on rotational protocol.
We kept voltage fixed at 70 kV; the exposure time was predetermined in 14 seconds.
We made some aquisitions in steps of 2 mA. The relationship between current and dose was linear with a R²=0,999.
| |
mA |
kV |
s |
mGy |
mm Al |
| 1 |
2 |
67.35 |
13.859 |
59.8 |
2.98 |
| 2 |
4 |
66.19 |
13.861 |
130.2 |
3.00 |
| 3 |
6 |
66.35 |
13.888 |
203.5 |
3.01 |
| 4 |
8 |
66.39 |
13.864 |
281.9 |
3.01 |
| 5 |
10 |
66,57 |
13.882 |
364.1 |
3.02 |
Fig. 9: Linearity of the dose. X-axis: current (mA). Y-axis: dose (mGy).
Keeping fixed the current at 10 mA,
we made complementary acquisitions at 50 kV,
60 kV and 80 kV.
We found a good stability of the apparatus in terms of voltages in a range of 5.4%.
| |
mA |
ideal selected kV |
real measured kV |
| 1 |
10 |
50 |
48.86 |
| 2 |
10 |
60 |
58.76 |
| 3 |
10 |
80 |
75.39 |
Using the PCXMC Monte Carlo software,
the effective dose of a SmartPan acquisition on an average patient (kV = 68; mA = 8; s = 22; rotation = 200°) has been measured from experimental data as 0.030 mSv.
Assuming a mean natural equivalent dose in Italy as 3.3 mSv per year per person,
this dose is about 3.3 days of natural exposition.
Our radiologic Department is serving a local health organization of 170,520 people; children 0-3 y/o are 6162; children 4-12 y/o are 12,369; over 12 y/o people are 151,989.
In first nine months of the activity of the Planmeca ProMax 3D unit we examined 2007 patients; no children 0-3 were examined; 290 patients were children 4-12 y/o.
| OPT in PEOPLE >= 4 y/o |
PED 4-12 |
ADULT >12 |
TOTAL >3 |
| Orthopantomography |
290 |
1717 |
2007 |
| No Orthopantomography |
12079 |
150272 |
162351 |
| TOTAL |
12369 |
151989 |
164358 |
2.34 % of children 4-12 living in our zone have been examinated by an orthopantomography in nine months,
face to a 1.13 % of adult people with a signifiant difference (p<0.0000,
Chi-Square with one degree of freedom = 139.96,
Chi-Square with one degree of freedom Yates-corrected = 138.95).
There is an odds-ratio = 2.10 between children 4-12 and adult people to undergo orthopantomography.
For a more refined calculation we have to add to our panoramic radiograms all those examinations made in other radiological departments.
Local databases can demostrate that in the same nine months 68 young people have been examinated elsewhere in public health services.
From this data,
we can estimate an annual rate of ortopantomographies on children 4-12 as about 35 exams per 1000 people per year living in our local health service.
So,
in our local health service,
during his / her childhood from 4 to 12 years old a boy or a girl has a 31.5% chance of being subjected to this examination in a public radiological department.
This rate may be even higher considering that there are some exams made in private dental offices and not counted by public health service.
