DRLs based on image quality assessment are the best optimization tool that plays a key role in optimization of patient doses and are also challenging task for technologists in patient dose reduction keeping image quality acceptable for diagnosis. Therefore, this study was conducted for the first time to establish AQD, image quality-related DRLs and SSDE for commonly performed CT procedures for adults of above 18 years as facility DRLs were not established earlier.

The concept of AQD and IQSC was employed by radiologists to assess the image quality and only images of acceptable quality were then used for dose analysis. It addressed the short comings of DRLs that were pointed out by Rehani [13] and the concept applied for the first time in Qatar [4] for pediatric study.

Certain interesting findings were revealed in this study. Initially, using the concept of AQD and IQSC, 264 out of 288 (almost 92%) CT exams were clinically acceptable to radiologists and had score of 03 while 24 (almost 8%) were excluded form dose analysis as they had score of 2 (5%) and 4 (3%), as shown in Fig. 2. Specifically, score-2 (nearly 5%) is not trivial as they were repeated. This suggests that there is a probability that a considerable number of exams that are not clinically acceptable are also counted in most dose surveys where image quality is not assessed and documented and the dose indices reported will not provide real values of clinically acceptable exams [4].

Image quality assessment sparked a new concept of Repeat Rejection Analysis (RRA) in CT that was not previously reported. Since, CT exposes patients to higher doses, has longer cycle times, and requires larger capital investment than either radiography or mammography, yet RRA for CT is neither suggested nor mandated by any regulatory bodies or professional organizations. In the current study repeat rate was observed 5% in the form of score-2 for CT procedures and 3% was of high-quality images (score-4) though it was not repeated but contributed unnecessary higher radiation dose to the patient. Rejection rate of the current study was 5% which is lower than AAPM [22] recommending limit of 10% for radiography while higher reported by Sean rose et al. 1.2% for CT [23]. Further breakdown of rejection in specific procedures is illustrated in Fig. 5.

Determination of rejection rate is crucial since it reveals the underlying causes for rejection which can be addressed in a better way to improve the image quality, lower the rejection rate, decrease patient radiation exposure, cut down cost, optimize machine performance, life along with reduction of staff burden and long waiting list.

For Brain CT, the median CTDIvol values for group-1, 2 and 3 were 25.8, 25.7 and 30.6 mGy while median DLP values were 496, 510 and 557 mGycm, respectively. The 75th percentile CTDIvol values for these groups were 30.2. 35.3 and 36.2 mGy and DLP values were 583, 619 and 781 mGycm, respectively. Similarly, the median SSDE values were calculated as 23.7, 22.3 and 28.8 mGy, while 75th percentile values were 29.3, 31.3 and 31.9 mGy, respectively. The effective dose calculated for group-2 was 1.2 mSv. All these values, mean, standard deviation and average circumference of head have been presented in Table 3.

As it clearly observed from Fig. 6, when the weight increases from goup-1 to group-3, exposure parameters (CTDIvol and DLP) increase proportionally. The size of the head remains relatively stable, showing only minor changes despite increases in age and weight. Therefore, a slight increase was observed in SSDE, CTDIvol and DLP values among the weight groups verifying our findings. All values approximately consistent between group-1 and 2 in terms of CTDIvol while a significant rise was observed in terms of both CTDIvol and DLP in group-3 due to increased head dimensions and range compared to group-1 and 2.

The image on the left displays AQD, 75th % of brain CT in terms of CTDI and SSDE, while the image on the right displays AQD and 75th % in terms of DLP, respectively

The median and 75th percentile values of CTDIvol and DLP become brain AQDs and DRLs for their corresponding weight groups, respectively. Similarly, the median and 75th percentile values in terms of SSDE become brain AQDs of SSDE and DRLs of SSDE for their corresponding weight groups, respectively. By comparing facility DRL (75th percentile value) of group-2 brain CT in terms of CTDIvol and DLP with other countries DRL such as Ireland [10], USA [11], Australia [20], UK [21], Canada [22], Japan [23] and Morocco [24], our facility DRL was found to be very low, as shown in Fig. 7, respectively. Facility DRL was also low from national DRLs suggested by regulatory body PNRA in the country [25].

Comparison of DRLs in terms of CTDI (left) and DLP (Right) of LRH (group-2) brain CT with other relevant studies

This reveals that prioritizing image quality over dose indices results in considerably lower doses without compromising image quality, showcasing safe practices and dose optimizations protocols being followed during imaging procedures.

For chest CT, the median CTDIvol values for group-1, 2 and 3 were 8.5, 8.7 and 14.3 mGy while median DLP values were 388, 377 and 605 mGycm, respectively. The 75th percentile CTDIvol values for these groups were 11.4, 14.6 and 17.9 mGy and DLP values were 501, 555 and 822 mGycm, respectively. Similarly, the median SSDE values were calculated as 12.2, 13.9 and 19.5 mGy, while 75th percentile values were 18.2, 20 and 23.7 mGy, respectively. The effective dose calculated for group-2 was 6.3 mSv. All these values, mean, standard deviation of CTDIvol and DLP have been presented in Table 4.

A gradual increase was noticed in median and 75th percentile values in terms of CTDIvol and DLP, especially in group-3, as patient’s weight was higher compared to group-1 and 2, as shown in Figs. 8 and 9. A similar result was noticed for SSDE value, which can be seen in Fig. 10. When weight increases, a correspondingly increase in exposure parameter is required to achieve adequate quality for accurate diagnosis, as evident from Fig. 8, 9 and 10. That is why the curve in Figs. 8, 9 and 10 gets steeper as weight increases.

The images display AQD (median) in terms of CTDIvol (left) and DLP (right) for chest, chest HRCT, abdomen KUB, and abdomen + pelvic CTs, respectively

The images display 75th % in terms of CTDIvol (left) and DLP (right) for chest, chest HRCT, abdomen KUB, and abdomen + pelvic CTs, respectively

The images display AQD-median (left) and 75th % SSDE (right) for chest, chest HRCT, abdomen KUB and abdomen + pelvis in terms of SSDE, respectively

The comparison of group-2 chest CT presented in Fig. 11 shows that facility DRLs in terms of CTDI were comparable to those of the USA, Canada, and Morocco’s DRL, whereas they were higher than DRLs of UK, Australia, Ireland and Morocco. In terms of DLP, DRLs of LRH chest CT were comparable to those of Canada and Japan’s DRL and less than Morocco’s, while higher than those of Ireland, the USA, Australia and the UK’s.

Comparison of DRLs in terms of CTDI (left) and DLP (Right) of LRH (group-2) chest CT with other relevant studies

The possible reasons behind the higher DRL for chest CT are the demand for high-quality images from reporting radiologists. It was challenging to report low-quality images since it was our first experience of optimizing patient doses in terms of quality acceptable for radiologist, rather than merely meeting dose requirements. This often result in repetition of procedure. Thus, it emphasizes the need for rigorous training of radiologists on image quality assessments, prioritizing the acceptance of images with some noise over unnecessarily crisp images.

For chest HRCT, the median CTDIvol values for group-1, 2 and 3 were 7.5, 10.7 and 13.7 mGy while median DLP values were 220, 448 and 538 mGycm, respectively. The 75th percentile CTDIvol values for these groups were 12.7, 15.9 and 18.9 mGy and DLP values were 427, 665 and 744 mGycm, respectively. Similarly, the median SSDE values were calculated as 12.1, 13.2 and 18.1 mGy, while 75th percentile values were 17.2, 19.6 and 24.9 mGy, respectively. The effective dose calculated for group-2 was 6 mSv. All these values, mean, standard deviation of CTDIvol and DLP have been presented in Table 5.

A proportional increase in the median and 75th percentile values of CTDIvol, DLP and SSDE for chest HRCT observed, as evident from Figs. 8, 9 and 10, respectively, as weight gets higher from group-1 to group-3. Comparing The 75th percentile values of chest HRCT for group-2 with other studies, our results show higher values than the DRLs of Ireland, the USA and the UK, both in terms of CTDIvol and DLP, as illustrated in Fig. 12. This study was conducted in a public sector hospital with high influx of patient undergoing CT procedures. It emphasizes the need for proper training of CT technologists in dose optimization protocols and encourages radiologists to report on images of adequate quality. Moreover, further optimization is needed to ensure patient safety.

Comparison of DRLs in terms of CTDI (left) and DLP (Right) of LRH (group-2) chest HRCT with other relevant studies

For abdomen KUB CT, the median CTDIvol values for group-1, 2 and 3 were 6.5, 6.8 and 13.9 mGy while median DLP values were 323, 350 and 624 mGycm, respectively. The 75th percentile CTDIvol values for these groups were 8.6, 11 and 19.4 mGy and DLP values were 444, 539 and 936 mGycm, respectively. Similarly, the median SSDE values were calculated as 9.8, 9.5 and 16.4 mGy, while 75th percentile values were 13.3, 16.3 and 24.8 mGy, respectively. The effective dose calculated for group-2 was 7.2 mSv. All these values, mean, standard deviation of CTDIvol and DLP have been presented in Table 6.

Similarly, for abdomen + pelvic CT, the median CTDIvol values for group-1, 2 and 3 were 8.2, 11.6 and 18.4 mGy while median DLP values were 449, 679 and 798 mGycm, respectively. The 75th percentile CTDIvol values for these groups were 16.2, 18.2 and 19.8 mGy and DLP values were 801, 1064 and 1169 mGycm, respectively. Similarly, the median SSDE values were calculated as 12.8, 13.8 and 25.2 mGy, while 75th percentile values were 23.1, 23.3 and 27.1 mGy, respectively. The effective dose calculated for group-2 was 10.2 mSv. All these values, mean, standard deviation of CTDIvol and DLP have been presented in Table 7.

A gradual increase was also observed in both abdomen KUB and abdomen + pelvic CT studies, as shown in Figs. 8, 9 and 10, respectively. Comparing the 75th percentile values with those of other relevant studies, the DRL of abdomen KUB for group-2 exhibited lower values in terms of CTDIvol and DLP compared to Australia, while it was higher than that of the UK, as illustrated in Fig. 13. However, this can be further restricted, as abdomen KUB is primarily performed for Renal stone localization, which can be visualized at low exposure and differentiated from other pathologies and lesions even in low-quality images [30].

Comparison of DRLs in terms of CTDI (left) and DLP (Right) of LRH (group-2) abdomen KUB CT with other relevant studies

Similarly, 75th percentile value of abdomen + pelvic of group-2 in terms of CTDIvol was comparable to Canada and Japan but lower than national DRL of PNRA. Regarding DLP, 75th percentile value of abdomen + pelvic was relatively higher than that of all relevant studies, as shown in Fig. 14. The raised values in exposure parameters (CTDIvol and DLP) are due to the requirement of high resolution and quality images demanded by radiologists. This requirement aims to missing minor pathologies and to prevent the unnecessary repetition of procedures. In addition, the unavailability of relevant facility DRL (FDRL) from the institute, which could have provided guidance during CT procedures, contributes to these high values.

Comparison of DRLs in terms of CTDI (left) and DLP (Right) of LRH (group-2) abdomen + pelvis CT with other relevant studies

For SSDE, the 75th percentile SSDE values of group-2 were compared with those of the USA, as depicted in Fig. 15. The 75th percentile values for chest and chest HRCT were slightly higher than those in the USA. Conversely, for abdomen KUB, the 75th percentile value was lower than that of the USA, whereas for abdomen + pelvic, it was higher. All these values were compared with the USA SSDE values, which had a diameter range from 29-33 cm, comparable to the effective diameter range of group-2 for corresponding procedures. Specifically, group-2, chest had an average effective diameter of 28 cm, chest HRCT 27 cm, abdomen KUB and abdomen-pelvic had an effective diameter of 28 cm as can be seen in Table 4–7, respectively.

Comparison of 75th % SSDE and effective dose of group-2 with USA and ICRP for Brain, chest, chest HRCT, abdomen KUB and abdomen + pelvic, respectively

Similarly, average effective doses of group-2 were compared with ICRP typical effective doses, showing that the effective doses of the Brain and chest were lower, while abdomen + pelvic value was approximately equal. Since, our study includes pelvic with the abdomen; this results in a slightly higher dose than abdomen KUB, as the combined and pelvic scan covered a wide range.

All the median and 75th percentile values of CTDIvol, DLP become facility AQDs and DRLs for their corresponding weight groups, respectively. Similarly, the median and 75th percentile values in terms of SSDE become AQDs of SSDE and DRLs of SSDE for their corresponding weight groups, respectively.

However, with the current values established, further work can be conducted to lower them once the staff are fully adapted to applying dose optimization protocols in daily routine procedures and the radiologists adhered to reporting and diagnosis at adequate image quality rather than demanding high-quality images. Thus, the AQD concept relies on the training and orientation of both technologists and radiologists. This is the beauty of AQD: it brings attention to the quality of the image, which directly affects patient dose and discourages the pursuit of unnecessary high quality. This represents a significant step toward fostering a culture of safe radiation practices.