Proposed DRLs for Mammography in Switzerland.

OBJECTIVES: The aim of this study is to propose Diagnostic Reference Levels (DRLs) values for mammography in Switzerland. Methods: For the data collection, a survey was conducted among a sufficient number of centres, including 5 University hospitals, several cantonal hospitals, and large private clinics, covering all linguistic regions of Switzerland to be representative of the clinical practice. The data gathered contained the mean glandular dose (MGD), the compressed breast thickness (CBT), the mammography model and the examination parameters for each acquisition. The data collected was sorted into the following categories: 2D or digital breast tomosynthesis (DBT) examination, craniocaudal (CC) or mediolateral oblique (MLO) projection, and 8 categories of compressed breast thickness (CBT) ranging from 20mm to 100mm in 10mm intervals. Results: 24762 acquisitions acquired in 31 centres on 36 mammography units from 6 different manufacturers were collected. The analysis showed that the data reflects the practice in Switzerland.The results revealed that the MGD is larger for DBT than for 2D acquisitions for the same CBT. From 20-30mm to 90-100mm of CBT, the 75th percentile of the MGD values obtained increased from 0.81mGy to 2.55mGy for 2D CC acquisitions, from 0.83mGy to 2.96mGy for 2D MLO acquisitions, from 1.22mGy to 3.66mGy for DBT CC acquisitions and from 1.33mGy to 4.04mGy for DBT MLO acquisitions. Conclusion: The results of the survey allow us to propose Swiss DRLs for mammography according to the examination type (2D/DBT), projection (CC/MLO) and CBT. The proposed values are very satisfactory in comparison with other studies. .

Effect of field of view (FOV) positioning and shielding on radiation dose in paediatric CBCT.

OBJECTIVE: To investigate the effect of two different large field of view (FOV) positions in the vertical dimension and shielding (thyroid collar and eyeglasses) on the effective dose and the local doses of various sites of the craniofacial complex. METHODS: Organ doses and effective doses were calculated based on the measured doses using 27 pairs of thermoluminescent dosemeters in a paediatric tissue-equivalent of a 10-year-old anthropomorphic phantom. The large FOV of the 3D Accuitomo F170 CBCT scanner was used to image parts of the craniofacial complex. Six protocols were performed: (A) cranial position without shielding; (B) cranial position with shielding; (C) caudal position without shielding; (D) caudal position with shielding, (E) similar to C with 3600 rotation and (F) similar to D with 360° rotation. Measurements were obtained in duplicate, and the relative δ value (%) was applied to compare the average doses between the protocols. RESULTS: Changing the FOV position from cranial to caudal without using shielding resulted in an increase of the effective dose of 18.8%. Use of shielding in the caudal position reduced the dose by 31.6%. Local absorbed dose of the thyroid had the most relevant impact on calculation of the effective dose, followed by oesophagus, bone marrow and bone surfaces, especially when comparing the different protocols. CONCLUSIONS: Application of shielding devices for thyroid in combination with a most caudal positioning of FOV led to the lowest local absorbed doses as well as the effective dose in a child phantom model.