S . Semghouli et al .: Radioprotection 2024 , 59 ( 2 ), 123 – 130 125
Table 1 . Distribution of the population studied by gender . |
Radiotherapy planning CT |
Diagnostic CT |
Gender |
Male |
Female |
Male |
Female |
|
48 ( 40 %) |
72 ( 60 %) |
66 ( 55 %) |
54 ( 45 %) |
Table 2 . Distribution of the population studied by age and BMI . Radiotherapy planning CT
Diagnostic CT Mean SD Min – Max Mean SD Min – Max
Age |
52 |
14.29 |
27 – 77 |
51 |
16.76 |
23 – 92 |
BMI |
25.71 |
3.02 |
20.10 – 32.36 |
24.34 |
3.13 |
17.15 – 30.07 |
Table 3 . Acquisition parameters per type of CT scan Radiotherapy planning CT-scans
Mean
Diagnostic CT-scans
Pulmonary embolism |
Infectious lung disease |
COPD |
|
Mean |
|
Pitch |
1 |
0.94 |
1.75 |
1.75 |
Voltage ( kV ) |
120 |
120 |
120 |
120 |
Intensity ( mAs ) |
90 |
125 |
150 |
150 |
Slice thickness ( mm ) |
2 |
1.25 |
1.25 |
1.25 |
Table 3 shows that the voltage used during diagnostic and radiotherapy planning CT-scans is 120 kV for all patients , and the intensity is modulated according to patient morphology and the protocol used . The average intensity for radiotherapy planning CT-scans is 100 mAs . In diagnostic CT-scans , the average intensity is 125 mAs for the pulmonary embolism protocol and 150 mAs for other protocols . The pitch is constant in radiotherapy planning CT-scans , and varies according to the protocol used in diagnostic CT-scans . The slice thickness is 1.25 mm and 2 mm for diagnostic CT-scans and radiotherapy planning CT-scans respectively .
The distribution of the CTDIvol , DLP and effective dose , as well as the diagnostic reference levels , are summarized in Tables 4 and 5 . Table 4 shows that the CTDI vol varies between 4 mGy and 35.20 mGy , with an average value of 14.58 mGy in radiotherapy planning CT-scans . The DLP value ranges from 215 mGy cm to 1606.80 mGy cm , with an average value of 735 mGy . cm . The effective dose ranges from 3.80 mSv to 28.44 mSv , with an average value of 13 mSv .
In diagnostic CT , the mean CTDIvol values for pulmonary embolism , infectious lung disease , and COPD were 9.64 , 9.14 , and 6.53 mGy , respectively . The mean DLP values were 367.15 mGy cm , 380 mGy cm , and 250.94 mGy cm for the same indications , respectively . The mean effective doses were 6.49 , 6.72 , and 4.44 mSv for the same indications , respectively .
Table 5 shows that the DRLs calculated in terms of CTDIvol and DLP for radiotherapy planning CT-scans were 19.37 mGy and 851.9 mGy cm , respectively . For diagnostic CT-scans , DRLs calculated in terms of CTDIvol were 11.13 mGy , 10.26 mGy , and 7.37 mGy for pulmonary embolism , infectious lung disease , and COPD , respectively . DRLs in terms of DLP were 417.73 mGy cm , 451.9 mGy cm , and 317.78 mGy cm for the same indications , respectively .
The distribution of the mean cancer risk associated with each CT-scan and the correlation of this risk with the CTDIvol , DLP and effective dose are illustrated in Tables 6 and 7 . As shown in Table 6 , the cancer risk for radiotherapy planning CTscans is ranged between 209 and 1564 with a mean value of 715 per 1 million . For diagnostic CT-scans , the cancer risk is ranged between 199 and 626 with a mean value of 357 per 1 million for pulmonary embolism , between 238 and 668 with a mean value of 369 per 1 million for infectious lung disease , and between 130 and 393 with a mean value of 244 per 1 million for COPD .
As summarized in Table 7 , in the radiotherapy planning CT-scans , the correlation coefficients ( p-values ) for gender , age , and BMI against effective dose are 0.076 , 0.212 , and 0.00 respectively .
Concerning diagnostic CT-scans , the correlation coefficients ( p-values ) for gender , clinical indication , age , and BMI against effective dose are 0.111 , 0.001 , 0.036 , and 0.231 respectively .
4 Discussion
This section discusses the main results of this study in the light of previous work and the recommendations of international bodies on radiation protection in medical imaging .