Material and Methods :
Our Material consists of national DRLs,
7 CT Scanners in 5 imaging centers of the same institution (Groupe 3R,
Switzerland) and 22 Radiologists.
All CT Scanners are connected to a single Dose Management Software (Dosewatch®),
with parameter uniformization and protocol Radlex mapping occurring before data collection.
Regarding protocol harmonization,
we designed an indication-based protocol map with 2 categories of patients for each protocol according to Body Mass Index (BMI < 25 and BMI > 25).
Protocol parameters have been harmonized according to clinical indication and BMI for:
- Detector configuration
- Reconstruction kernel
- Pitch
- Tube rotation time
- mA modulation
- Noise index
- Filtering
- Reconstruction standardization
The purpose of this harmonization was thus not dose reduction,
but only protocol mapping and harmonization among different centers according state-of-the-art parameters.
We compared DRLs of institutional anatomy-based and indication-based protocols :
- To national DRLs
- To each other (Fig. 1).
The onesample Wilcoxon signed rank and the MannWhitney tests were used to assess statistical significant differences among groups,
as appropriate.
Results
- "Institutional DRLs" mean median CTDI values for the 7 CT scanners of Groupe 3r
- "CTDI" means median CTDI values
- "national DRL" = P75 unless stated differently
- p<0.05 indicates a statistically significant difference
The 11 most used protocols among chest and abdomen CT examinations were analysed,
representing 70% of the total institutional examinations.
The study population consisted of 660 chest and 2305 abdomen CT examinations.
The BMI ratio <25 and >25 was respectively 50%/50% for chest and 52%/48% for abdomen.
Main indications (BMI<25 / BMI>25) were
- for chest CT examinations: pulmonary embolism (36%/30%),
pneumonia (34%/47%) and emphysema (30%/23%),
- for abdomen CT examinations: diverticulitis (19%/27%),
liver lesions (17%/18%),
kidney stones (16%/15%),
renal tumor (16%/6%),
CT colonography (10%/10%), pancreas (9%/8%),
appendicitis (8%/9%) and renal infection (8%/7%).
1.
Comparison of institutional DRLs based on anatomical region to national DRLs based on anatomical region protocols
Institutional DRLs based on anatomical region protocols were:
- Significantly lower than national P75 DRL for total study population abdomen and chest CT
- Significantly lower than national P25 DRL for BMI<25 abdomen CT
- Significantly lower than national P75 DRL for BMI<25 chest CT
- Significantly lower than national P75 DRL for BMI>25 abdomen and chest CT
1.1.
Institutional DRLs (median CTDI) for the entire study population were significantly lower than national DRLs,
respectively 6.3mGy for chest (national P75 = 10mGy) and 8.2mGy for abdomen (national P75 = 15 mGy) ( Fig. 2 ).
1.2.
For BMI<25 patients,
median CTDI values based on anatomical region protocols were 4.7mGy for chest and 6.6 mGy for abdomen and were:
- Significantly lower than national DRLs (national P75 = 10mGy for chest and 15mGy for abdomen)( Fig. 3 )
- Significantly lower than national P25 DRL for abdomen (national P25 = 10mGy)
- Significantly lower than national P75 DRLs for chest (national P75 = 10mGy).
1.3.
For BMI>25 patients,
institutional DRLs based on anatomical region protocols were significantly lower than national P75 DRLs.
Median CTDI values were 8.5mGy for chest (national P75 = 10mGy) and 10.5mGy for abdomen (national P75 = 15mGy) ( Fig. 4 ).
2.
Comparison of institutional DRLs based on clinical indication protocols to national DRLs based on anatomical region protocols
Institutional DRLs based on clinical indication protocols were:
- Significantly lower than national P75 DRL for total study population abdomen and chest CT
- Significantly lower than national P25 DRL for BMI<25 abdomen and chest CT,
except for emphysema
- Significantly lower than national P75 DRL for BMI>25 abdomen and chest CT
2.1.
Institutional DRLs (median CTDI) for the entire study population were significantly lower than national P75 DRLs based on anatomical region protocols,
with a large variation in dose levels per clinical indication (Fig. 5).
2.2.
For BMI<25 patients,
institutional median CTDI values based on clinical indication protocols were lower than national P25 DRLs,
except for emphysema (significantly lower than P75) ( Fig. 6 ).
2.3.
For BMI>25 patients,
institutional median CTDI values based on clinical indication protocols were significantly lower than national P75 DRLs for all indications (Fig. 7).
3.
Comparison of institutional DRLs for CHEST CT examinations based on clinical indication protocols to institutional DRLs based on anatomical region protocols
For Chest CT,
institutional DRLs based on clinical indication and compared to anatomical region protocols:
- were significantly lower for all indications in the total population (n=660,
median CTDI=6.3mGy): emphysema (CTDI 5.6mGy,
p=0.0343),
pneumonia (CTDI 5.8mGy,
p=0.0289) and pulmonary embolism (CTDI 7.2mGy,
p=0.0004).
- were significantly lower for pneumonia (CTDI 4.3mGy,
p=0.0207) and pulmonary embolism (CTDI 5.2mGy,
p=0.0076) in BMI<25 patients (n=333,
median CTDI=4.7mGy).
- were not significantly lower for any indication in BMI>25 patients (n=327,
median CTDI=8.5mGy).
4.
Comparison of institutional DRLs for ABDOMEN CT examinations based on clinical indication protocols to institutional DRLs based on anatomical region protocols
For Abdomen CT,
institutional DRLs based on clinical indication and compared to anatomical region protocols:
- were significantly lower for specific indications in the total population (n=2305,
median CTDI=8.2mGy): CT colonography (CTDI 6.2mGy,
p<0.0001),
diverticulitis (CTDI 10mGy, p<0.0001),
kidney stones (CTDI 7.8mGy,
p=0.0231),
liver (CTDI 8.9,
p=0.0126) and pancreas (CTDI 7.3mGy,
p=0.0002).
- were significantly lower for specific indications in BMI<25 patients (n=1196,
median CTDI=6.6mGy): CT colonography (CTDI 5mGy,
p<0.0001), diverticulitis (CTDI 7.7,
p<0.0001) and pancreas (CTDI 6.3mGy,
p=0.0065).
- were significantly lower for specific indications in BMI>25 patients (n=1109,
median CTDI=10.5mGy): CT colonography (CTDI 7.2mGy,
p<0.0001), diverticulitis (CTDI 12.2,
p<0.0001),
kidney stones (CTDI 9.9mGy,
p=0.0065) and pancreas (CTDI 9.3mGy,
p=0.008).