Radioprotection No 59-1 | Page 58

52 O . Nhila et al .: Radioprotection 2024 , 59 ( 1 ), 50 – 54

Fig . 1 . Distribution of CTDIvol values for CT-RT breast cancer . Fig . 2 . Distribution of PDL values for CT-RT breast cancer .

changes to the radiation protection system . For this , Moroccan Agency for Nuclear and Radiological Safety and Security ( AMSSNuR ) is developing a regulatory project that consists of establishing and utilizing DRLs . This project has resulted in several published surveys of DRLs in different medical imaging modalities .

No previous study has been published on DRLs for CT protocols in radiotherapy in a Moroccan hospital . Therefore , the present study has been performed to establish local DRLs for breast cancer CT-RT protocols .

The results obtained show that the 75th percentile of CTDIvol and DLP for breast cancer CT-RT protocols are considerably lower than those of the European countries listed in Table 2 . The UK comes closest to the DRLs in our study , with CTDIvol and PDL values of 10 mGy and 390 mGy . cm , respectively .

There are several possible reasons for these wide variations . The main reason seems the difference between CT protocols and scanner brands , and generations ( Kumsa et al ., 2023 ). In addition , disparities in operator training and experience , which vary from one country to another , may contribute to variations in exposure levels ( Tahiri et al ., 2022 ).

Moreover , even within the same country , significant dose differences may exist between centers , usually due to the lack of a standardized protocol . In some cases , the cause of these differences is difficult to explain . For instance , a study conducted to establish DRLs for the breast cancer CT-RT protocol by O ’ Connor et al .( O ’ connor , Ardle and Mullaney ,

2016 ) concluded that significant dose differences between CT radiotherapy centers were unjustifiable .

When comparing the dosimetric indicators for CT-RT breast cancer in the UK with our own , we observed that despite the longer scan length values in this study ( median value of 420 mm versus 280 mm ), the DLP values are lower than those in the UK . Thus , when comparing the acquisition parameters published in the two surveys , it seems that the principal causes of the differences between CTDIvol and DLP relate to acquisition parameters affecting dose , such as FOV , mas , slice thickness and pitch as demonstrated in previous studies ( Davis et al ., 2018 ).

Worldwide data on DRLs for CT-RT breast cancer are scarce . Thus , even though the doses of our study are lower than those of previous studies , they seem insufficient to confirm the optimality of our results . In this context , we were required to compare the results of DRLs for CT-RT breast cancer against those of thoracic diagnostic CT protocols , similar to the study conducted by Connor et al .

In this context , for a complete analysis , it was necessary to compare the results of this study with those of our previous study , establishing LDRLs in Morocco for adult CT scans of different localizations , including the chest ( El Mansouri et al ., 2022 ). The results obtained show that the 75th percentile of CTDIvol and DLP of the chest CTwere approximately twice as high ( 12.3 mGy and 632 mGy cm ) as those proposed in the present study . This difference can be explained by the effect of