DRL for plain radiography
Compared to the previous DRL,
established in 2010 [3],
dose-relevant parameters could be decreased by 20%,
on average (see Fig. 1).
Relative changes of the DRL for conventional plain X-ray radiography showed a decrease by about 40% between 2003 and 2010.
The main reason for this rather big difference is that at the time of introducing DRL in 2003 [4] only a small database of dose values in terms of dose area products (DAP) was available.
This changed substantially for the 1st update,
when the underlying database was much more comprehensive due to strong efforts in recording dose values in daily practice.
Therefore the changes in the 2nd update were not as pronounced as in the first one and showed a mean decrease of about 15%.
Two new exams have been introduced in 2016 namely shoulder (per view) and hip (per view).
Also the DRL for children were adapted and the classification scheme regarding age and weight according the ICRP publication [5] was used.
As an example see the listed changes for the DRL of the MCU exam (micturating cysto-urethrogram) in Table 1.
Consequences for mammographic screening in Germany
With the 2nd modification of the DRLs in 2016,
the DRL for one examination of the breast was lowered from 2.5 mSv to 2.0 mSv.
To estimate the impact of the 2nd modification of the DRLs for the mammography screening in Germany,
more than 1.8 million exposures from 114 mammography system form 2016 (Jan to Aug) were analyzed.
113 DR-Systems and 1 CR-Systems.
Fig. 2 includes only the 20 systems with the highest mean average glandular Dose (AGD).
The mean AGDs of 10 systems were above the new DRL.
Surprisingly the only CR-System (ID_11) was not under the first 10 systems.
However,
internal studies of the reference center Münster have shown [6],
that the displayed AGD of CR-System deviates an average of 20% downwards.
Therefore it must be assumed,
that the real mean AGD of the CR-System is above 2 mSv.
The manufactures and system types are listed in Table 2.
DRL for CT
More CT exams appeared in the publications of DRL in 2016 according to the common changes in imaging techniques,
especially the angiography exams of the carotis,
the triggered coronal CTA and the CTA of pelvis and extremities (see Fig. 3).
What is missing in the RDLs for CT procedures of adults is a value for CT perfusion of the brain.
This limitation is caused by the very small number of reported dose values and the possible sources of errors due to a variety of different protocols,
different tube voltages used and also different number of scans.
DRLs for CT examination of children (with the exception of the head values) are reported with respect to the 32 cm PMMA phantom (body phantom) for a better correlation with the displayed values at the operator console.
Differences for high contrast and low contrast imaging in CT
The updated DRL for CT present for several anatomical regions depending on the issue of the examination low- and high-contrast values.
The low-dose protocols vary significantly in many parameters like kVp,
slice thickness,
kernel or windowing.
The quite different ratios of the CTDIvol values (see Table 3) show,
that the potential of optimisation exists furthermore.
A differentiation of the examinations in respect of the issue is of major importance.
DRL for fluoroscopy and interventional radiology
The adjusted values for fluoroscoy can be found in Fig. 4.
But with respect to the increasing imaging techniques in radiological interventions,
there was the need for establishing DRLs for common interventional procedures.
While in 2010 only PTA and PTCA were listed as interventional radiological exams,
in 2016 DRLs for 13 procedures have been published,
including PCI,
TAVI,
TACE EVAR and PTA.
Comparing DAP values for exams of adults in the abdominal region we can find always approximately a factor of 10 when switching from plain radiography (Abdomen AP: 230 cGy*cm²) to fluoroscopy (Colon Contrast Enema: 3.000 cGy*cm²) and to abdominal interventions (EVAR and TACE: 30.000 cGy*cm²).