Radiation Dose Optimization Based on Saudi National Diagnostic Reference Levels and Effective Dose Calculation for Computed Tomography Imaging: A Unicentral Cohort Study

Round 1

Reviewer 1 Report

In this study the radiation dose of CT head, chest, abdomen and pelvis was optimized by means of the CTDIvol and DLP of 3000 participants from 1 hospital in Saudi Arabia. In addition, the optimized doses were used to calculate a local Diagnostic Reference Level (NDRL) which was compared to the NRDL of Saudi Arabia and other countries.

Major comments

Although the data of 3000 participants in CT examinations could provide interesting results in dose distributions, and image quality optimization, no such data is presented. Please provide data (eg in histograms) of dose distributions. In addition, demographic data on the patient population is missing. Please provide information on age, gender, etc. Moreover, from the presented data it is not clear how the dose data was calculated. Were only blank CT scans included, or also contrast and more phase scans? And if so, which dose data was then used? Please be more specific about the inclusion criteria and the dose data.

It is not clear how the CT protocols were optimized. Optimization of dose should include assessment of diagnostic image quality, however, no data on image quality is included.

In addition to the DRL also achievable dose levels are defined for CT. I miss this in the results and discussion. Please add the achievable dose levels.

Minor comments

Abstract

Please add quantitative data to the result section. Almost the whole abstract consist of introduction and method section. A clear conclusion is missing.

Introduction

In addition to tube current modulation and automatic current selection, modern CT scanners also provide automatic tube voltage selection. Was this option not available on the CT scanners used?

Materials and Methods

Which CT scanners were included in the study? A Siemens AS and a Flash are mentioned. Does this mean that 1 AS and 1 Flash were used? Why is the AS characterized as kV 120 and the Flash as kV 140? Does this mean that only 120 and 140 kVp scans were included, respectively?

A large series of scan parameters were analyzed: mAs, kVp, exposure time, etc. However, no statistical analysis of all these parameters is provided. Please add this data. What is meant by exposure time (ms)?

It is not clear to me why CT-Expo was used since it is mentioned that this software provides data on CTDIvol and DLP. However, this data is also provided by the CT scanner. Which data was used for the patient dose data? And why was CT-Expo used?

From 280 patients dose data was missing. However, providing patient dose data is obligatory. So how can dose data be missing?

In fig 2 and example of the patient dose report is presented. However, since all dose data was extracted by Teamplay (?) I don’t think this information is needed. I suggest to omit this figure.

Patient data was extracted from jan 2019 to dec 2021. The IRB approval dated jan 2022. Why was informed consent obtained from each patient prior to imaging? This looks like data was retrospectively extracted from the PACS system (or Teamplay), and the study design was not prospective. However, it is mentioned that the study had an ambispective design, that is both retrospective and prospective data. It is unclear which data was used retrospectively and which data was used prospectively. Please be more clear on this point.

Results

The dose parameters for all patients were set at an average kV of 120 for all scanned body organs. This is unclear. I presume that the scan parameters were extracted from the actual CT scans? So what does this mean?

Table 1 does not present mean values with standard deviations (or median with range or confidence intervals) for the different parameters. I do not understand the value of e.g. 120 kV for abdomen CT. What does this mean? That all patients were scanned with 120 kV, independent of body size? Also there seems to be no variation in mAs and pitch. Please clarify. The mAs value in table 1, does is represent the quality reference mAs or a fixed mAs? In addition, the calculation of effective dose is unclear. Please clarify how ED was calculated from the actual patient dose parameters.

Table 2. Diagnostic Level Product should be Dose Length Product? 

The data in table 3 may be calculated with CT-Expo? This table provides a comparison of organ dose in the current study (after dose optimization?) with respect to other studies. However, comparison of organ dose is not within the scope of the study. For clarity I suggest to omit these results.

Discussion

In general the discussion is way too lengthy, too fragmented with too many paragraphs. Please try to combine paragraphs with a clear focus and a clear discussion point and message. At this moments the aim of all these short paragraphs is not clear. 

The last two paragraphs of the discussion (just above the limitations) can be omitted. They discuss the comparison of the Saudi NDRL with other studies on NDRLs and a comparison of the organs doses. However, both discussion are not within the scope of this study.

Limitations

It is mentioned that the data was acquired from a single unit. What is meant by one unit? One hospital with two CT scanners?

The data was retrospectively acquired. Why is it mentioned that retrospectively acquired data is prone to confounding bias, poor follow-up and absence of statistics?

I do not understand the statement about biased discussions from the authors, and selection of controls. Please be more clear about what exactly the limitation is here.

The data of the study was acquired within 5.5 months. However the inclusion of data was from jan 2019 to dec 2021. Please clarify.

Why do the authors think that 3000 patients is not enough and that this sample size is inadequate? Since no statistical analysis is performed, it is hard to see why this might be true.

Why do the authors think that the estimations made in the study are subject to uncertainty? What estimations do you refer to? And what are the uncertainties?

Why was mammography included in the study?

Please omit the two paragraphs on future scope of the research. I think the are outside the scope of this research

Conclusion

The conclusion does not give an answer on the research questions: (1) establishment of optimized CT protocols and (2) establishment of local DRL. The statement on effective dose and organ dose values was not within scope of the study. Please rephrase the conclusion.

Abbreviations

Many abbreviations are not used in the manuscript: AAPM, CAP, CTPA, DICOM, PACS, KPI and SSDE. Please correct.

Author Response

Reviewer 1

Comments and Suggestions for Authors

In this study the radiation dose of CT head, chest, abdomen and pelvis was optimized by means of the CTDIvol and DLP of 3000 participants from 1 hospital in Saudi Arabia. In addition, the optimized doses were used to calculate a local Diagnostic Reference Level (NDRL) which was compared to the NRDL of Saudi Arabia and other countries.

Response: Thank you.

Major comments

• Although the data of 3000 participants in CT examinations could provide interesting results in dose distributions, and image quality optimization, no such data is presented. Please provide data (eg in histograms) of dose distributions.

Response: We would like to thank you for this valuable comment.

Figure 2 (linear histogram) has now been incorporated into the manuscript detailing radiation distribution data as requested.

Figure 2. Distribution of effective dose across the study period

Linear histogram showing the distribution of effective dose across the study period (Midline: to separate pre- and post- optimization phases).

 

• In addition, demographic data on the patient population is missing. Please provide information on age, gender, etc.

Response: Thank you for this comment.

We agree that the demographic details should have mentioned the patient population. Thus, in this re-submission, demographics have now been added to the patient population.

‘The enrolled patients ranged in age from 18 to 83 years (1823 Males and 1177 Females).’

• Moreover, from the presented data it is not clear how the dose data was calculated. Were only blank CT scans included, or also contrast and more phase scans? And if so, which dose data was then used? Please be more specific about the inclusion criteria and the dose data.

Response: We do agree that our previous version slightly lacked a clear concept regarding how contrast-enhanced studies' dose data were calculated. However, we are grateful for your comments and have extensively amended the manuscript. As a result, the manuscript methodology (i.e., Dosimetry) has been clearly organized.

‘Monte Carlo CT-Expo version 2.5 software (Germany) was used for dose calculations. This was applied to contrast-enhanced and blank (i.e., non-contrast-enhanced) studies. Dose estimation was performed based on the averages obtained from all CT examinations on mathematical phantoms for adults (ADAM and EVA) (Figure 1)^*.’

^{*Hart D, W.B.F. Population dose from medical X-ray examinations. Eur. J Radiol. 2004 June}

• It is not clear how the CT protocols were optimized. Optimization of dose should include assessment of diagnostic image quality, however, no data on image quality is included.

Response: In this re-submission, we re-defined how our CT protocols were optimized to be more explicit for readers.

We also defined optimized CT protocols in our methodology.

‘The optimized protocols in this study were defined by the resultant post-optimization protocols in relation to NDRLs with significantly reduced radiation doses to patients and their organs, which were implemented in our department.’

• Optimization of dose should include assessment of diagnostic image quality, however, no data on image quality is included.

Response: Thank you for this valuable comment.

In medical imaging, national Diagnostic Reference Levels guide physicians in managing radiation doses while maintaining a good imaging quality.

In 1996, the International Commission on Radiological Protection (ICRP) established diagnostic reference levels (DRLs) as benchmarks for identifying abnormally high radiation doses and optimizing radiation protection and image quality. ^*,**

This study focused merely on optimizing radiation protection in CT imaging. This was implicated by reducing the radiation doses to the patients and their exposed organs, enabling us to correlate with NDRLs in the KSA^*** , and adhere to international guidelines for radiation exposure. It did not assess the image quality which is beyond the scope, and has now added to our study limitation in this re-submission.

However, quality control of ionizing radiation exposure was extensively explored in this study based on references from the Saudi Food and Drug Authority (SFDA) that recently established the National Diagnostic Reference Level^* measured by CTDI and DLP.

^{*European Commission, Food and Agriculture Organization of the United Nations, International Atomic Energy Agency, International Labour Organization, OECD Nuclear Energy Agency, Pan American Health Organization, United Nations Environment Programme, World Health Organization, Radiation Protection and Safety of Radiation Sources: International Basic Safety Standards: General Safety Requirements Part 3, No. GSR Part 3, IAEA, Vienna (2014).}

^{**International Atomic Energy Agency (IAEA). Radiation Protection and Safety in Medical Uses of Ionizing Radiation, IAEA Safety Standards Series No. SSG-46, IAEA, Vienna (2018).}

^{*** Saudi Food and Drug Authority: Medical Devices Sector. National Diagnostic Reference Levels (NDRL) Computed Tomography (CT) – Adult; 2021. Available from: https://sfda.gov.sa/sites/default/files/2020-08/%28NDRL%29En.pdf. Accessed April 30, 2022.}

In addition to the DRL also achievable dose levels are defined for CT. I miss this in the results and discussion. Please add the achievable dose levels.

Response: Thank you for this valuable comment. The dose indices after optimization reflect our department's achievable doses (ADs). This was added to the footnotes of results tables, i.e., (Table 1) and (Table 2). 

Minor comments

Abstract

• Please add quantitative data to the result section. Almost the whole abstract consist of introduction and method section. A clear conclusion is missing.

Response: Thank you for your valuable comment.

In this version, we have revised the abstract message, and with the aid of your constructive comments, we have added quantitative measures and better conveyed the conclusion.

Introduction

• In addition to tube current modulation and automatic current selection, modern CT scanners also provide automatic tube voltage selection. Was this option not available on the CT scanners used?

Response: Thank you for this comment. Unfortunately, the available CT equipment in our facility is from Siemens™, Germany (SOMATOM Definition AS 64-slice kV 120 and SOMATOM Definition flash dual-source 128-slice kV 140) and does not provide this feature.

Materials and Methods

• Which CT scanners were included in the study? A Siemens AS and a Flash are mentioned. Does this mean that 1 AS and 1 Flash were used?

Response: Indeed, both scanners were included in the study.

‘All CT examinations were performed using two commercially available CT devices (SOMATOM Definition AS 64-slice kV 120 and SOMATOM Definition flash du-al-source 128-slice kV 140, Siemens™, Munich, Germany).’

• Why is the AS characterized as kV 120 and the Flash as kV 140? Does this mean that only 120 and 140 kVp scans were included, respectively?

Response: Thank you for this comment. Exactly, only 120 and 140 kV scans were included from our facility.

• A large series of scan parameters were analyzed: mAs, kVp, exposure time, etc. However, no statistical analysis of all these parameters is provided. Please add this data. What is meant by exposure time (ms)?

Response: Thank you for this comment. Statistical analysis was conducted for these parameters with an unpaired t-test of independence computed to compare these continuous variables. We have mentioned the results of hypothesis testing (i.e., P value) in Table 1. This was clarified further in the Table footnote of this re-submission. 

‘՟ Statistical tests were conducted at a significance level of 0.05. Comparison of the pre-optimization phase with the post-optimization phase using an unpaired t-test of independence’

It is not clear to me why CT-Expo was used since it is mentioned that this software provides data on CTDIvol and DLP. However, this data is also provided by the CT scanner. Which data was used for the patient dose data? And why was CT-Expo used?

Response: CT-Expo offers dose calculations for pre-defined standard CT examinations; the selection of the scan range is made automatically and for both sexes simultaneously, with different sets of scan parameters. It allows analysis of any significant differences. Therefore, results may be used for subsequent optimization of scan protocols.

From 280 patients dose data was missing. However, providing patient dose data is obligatory. So how can dose data be missing?

Response: Thank you for this comment. Data were missing because in our department, we used to depend on manual documentation of dose indices utilizing hardcopies which are liable for missing on a few occasions. However, currently, we replaced this method with an automated registry.

• In fig 2 and example of the patient dose report is presented. However, since all dose data was extracted by Teamplay (?) I don’t think this information is needed. I suggest to omit this figure.

Response: Thank you for this comment. Figure 2 has been deleted as per requested.

• Patient data was extracted from jan 2019 to dec 2021. The IRB approval dated jan 2022. Why was informed consent obtained from each patient prior to imaging? This looks like data was retrospectively extracted from the PACS system (or Teamplay), and the study design was not prospective. However, it is mentioned that the study had an ambispective design, that is both retrospective and prospective data. It is unclear which data was used retrospectively and which data was used prospectively. Please be more clear on this point.

Response: Thank you for this valuable input. Our IRB approval was initially obtained before January 2022. However, we revised our methodology based on a pilot study to conduct this ambispective study. Thereafter, we granted another amended approval from our institutional research ethics committee to ensure full compliance with research ethics (attached in this resubmission).

‘The rationale behind the ambispective design in this study was that the study patients were divided into two equal groups to study the impact of the optimization effect on radiation doses: A) pre-optimization phase (1500 patients); those imaged on or before June 1, 2021 (January 1, 2019, to June 30, 2020 [1.5 y]) and B) post-optimization phase (1500 patients); those imaged after June 30, 2020 (July 1 to December 30, 2021 [1.5 years]).

Retrospective retrieving and prospective registering of data by utilizing a software was conducted before and after radiation exposure via CT imaging. Comparative ambispective/ambidirectional design with a fixed interval (e.g., 1.5 years before and 1.5 years after optimization of dose measures) has reasonable scientific merit for studying the impact of dose optimization across time.^*,**’

^{*Lazcano G, Papuzinski C, Madrid E, Arancibia M. General concepts in biostatistics and clinical epidemiology: observational studies with cohort design. Medwave. 2019 Dec 16;19(11):e7748. Spanish, English. doi: 10.5867/medwave.2019.11.7748. PMID: 31999676.}

^{**Commenges D, Moreau T. Comparative efficiency of a survival‐based case‐control design and a random selection cohort design. Stat Med. 1991;10(11):1775–1782.}

In this re-submission, we re-arranged our methodology to be more precise for readers, and amended these sentences to the study design for better clarity.’

Results

• The dose parameters for all patients were set at an average kV of 120 for all scanned body organs. This is unclear. I presume that the scan parameters were extracted from the actual CT scans? So what does this mean?

Response: Thank you for your valuable comment. All patients in this study were of average body size with no significant obesity, and they were scanned with standard protocol in our hospital i.e. 120 kV.^*

^{* Romans L. Computed Tomography for Technologists: A comprehensive text. Lippincott Williams & Wilkins; 2018 Aug 7.}

Table 1 does not present mean values with standard deviations (or median with range or confidence intervals) for the different parameters.

Response: Thank you for this valuable input.

Table 1 presents values in means± standard deviations. This was added in this re-submission to the footnote of Table 1 and amended in the table title.

• I do not understand the value of e.g. 120 kV for abdomen CT. What does this mean? That all patients were scanned with 120 kV, independent of body size? Also there seems to be no variation in mAs and pitch. Please clarify.

Response: Thank you for your valuable comment. All patients in this study were of average body size with no significant obesity, and they were scanned with standard protocol in our hospital i.e. 120 kV.^*

^{* Romans L. Computed Tomography for Technologists: A comprehensive text. Lippincott Williams & Wilkins; 2018 Aug 7.}

• The mAs value in table 1, does is represent the quality reference mAs or a fixed mAs? In addition, the calculation of effective dose is unclear. Please clarify how ED was calculated from the actual patient dose parameters.

Response: Thank you for this comment. As mentioned in our methodology (i.e., data collection), mAs in Table 1 represent the mean values of the produced radiation. For clarity, this was added to the Table footnote in this re-submission.

• Table 2. Diagnostic Level Product should be Dose Length Product?

Response: Thank you for this valuable comment. Yes, we agree with the reviewer, and Table 2 was revised and amended accordingly.

• The data in table 3 may be calculated with CT-Expo? This table provides a comparison of organ dose in the current study (after dose optimization?) with respect to other studies. However, comparison of organ dose is not within the scope of the study. For clarity I suggest to omit these results.

Response: The authors believe that organ dose exposure is part of the study’s scope, especially in studying the effective dose and its impact on radiation-sensitive organs. Therefore, we prefer to keep these crucial results. Kindly consider the improvements that have been made in this version.

Discussion

• In general the discussion is way too lengthy, too fragmented with too many paragraphs. Please try to combine paragraphs with a clear focus and a clear discussion point and message. At this moments the aim of all these short paragraphs is not clear.

Response: Thank you for this comment. The discussion section was revised according to suggestions from the respectable reviewer.

• The last two paragraphs of the discussion (just above the limitations) can be omitted. They discuss the comparison of the Saudi NDRL with other studies on NDRLs and a comparison of the organs doses. However, both discussion are not within the scope of this study.

Response: I am very grateful to you for pointing this out; both paragraphs have been deleted as per requested.

Limitations

• It is mentioned that the data was acquired from a single unit. What is meant by one unit? One hospital with two CT scanners?

Response: I am very grateful to you for pointing this out; this is exactly the meaning of 1 facility (i.e. Unicentral) and two scanners. This is clarified in the re-submitted manuscript for better clarity for readers. 

• The data was retrospectively acquired. Why is it mentioned that retrospectively acquired data is prone to confounding bias, poor follow-up and absence of statistics?

Response: I am very grateful to you for pointing this out; the retrospective part of the study is liable for confounding bias, etc., of retrieved, and that’s why we have mentioned it. However, to avoid ambiguity, we deleted this sentence in this re-submission. 

• I do not understand the statement about biased discussions from the authors, and selection of controls. Please be more clear about what exactly the limitation is here.

Response: Thank you for pointing this out; and to avoid ambiguity, we deleted this sentence in this re-submission. 

• The data of the study was acquired within 5.5 months. However the inclusion of data was from jan 2019 to dec 2021. Please clarify.

Response: This comment has been addressed accordingly in this re-submission. The sentence that mentioned ‘5.5 months’ was deleted.

• Why do the authors think that 3000 patients is not enough and that this sample size is inadequate? Since no statistical analysis is performed, it is hard to see why this might be true.

Response: This comment has been addressed accordingly in this re-submission. The sentence that mentioned the typo ‘inadequate’ was deleted.

• Why do the authors think that the estimations made in the study are subject to uncertainty? What estimations do you refer to? And what are the uncertainties?

Response: This comment has been addressed accordingly in this re-submission. The sentence that mentioned the typo ‘estimations’ was deleted.

• Why was mammography included in the study?

Response: This comment has been addressed accordingly in this re-submission. The sentence that mentioned the typo ‘mammography’ was deleted.

• Please omit the two paragraphs on future scope of the research. I think they are outside the scope of this research

Response: In this re-submission, we make sure to omit the two paragraphs on the future scope of the research. We kept only paragraphs which are intimately related to our study subject.

Conclusion

• The conclusion does not give an answer on the research questions: (1) establishment of optimized CT protocols and (2) establishment of local DRL. The statement on effective dose and organ dose values was not within scope of the study. Please rephrase the conclusion.

Response: Thank you for your valuable comments. The conclusion has been revised and clearly presents our answers to the research question in this re-submission.

Abbreviations

• Many abbreviations are not used in the manuscript: AAPM, CAP, CTPA, DICOM, PACS, KPI and SSDE. Please correct.

Response: Thank you for your valuable comments. The abbreviations have been revised in this re-submission.

 

In this version, we have revised the paper’s message, and with the help of your constructive comments, we were able to convey the study's aim and findings to the reader. Further, we were able to improve the description of our method to ensure its clarity and reproducibility. Our final results are scientifically sound and of plausible strength. Kindly consider the improvements that have been made in this version.

We have incorporated the changes suggested by the first reviewer in the revised manuscript. We hope that we have adequately addressed all the issues raised and that our manuscript is now suitable for publication in applied sciences.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments for author File: Comments.pdf

Author Response

Reviewer 2

Referee report

Article ID: applsci 1977008

Title: Radiation Dose Optimization Based on Saudi National Diagnostic Reference Levels for Computed Tomography Imaging: A Unicentral Comparative Cohort Study

General Comments

The aim of this research was aimed to attain optimized CT examination protocols to lower patients’ radiation and organ doses during head, chest, abdomen, and pelvis CT examinations and to establish institutional DRLs as a benchmark that would enable us to correlate with NDRLs in the KSA and adhere to international guidelines of radiation exposure. I think that this kind of paper is important to applsci readers, however, I have a few questions and suggestions in article sections. So, after to respond favourably to all these questions and suggestions, in my opinion, the paper can be accepted for publication.

Response: Thank you.

• According to ICRP 135 report, since it is only used radiological equipment, the most correct thing would be to speak of Typical Value for its study. See table 2.2 ICRP 135 report.

Response: I am very grateful to you for pointing this out; this was implemented in this re-submission by speaking of typical value in the methodology and conclusion sections.

• Some specific comments:

Introduction

1. Page 2.
2. Line 54. You should expand the introduction section, adding support bibliography to justify your work. Should you use ICRP 135 report.

Response: This comment has been addressed accordingly in this re-submission. In addition, we ensure to include ICRP 135 report in our introduction as a supportive bibliography.

Must you to respond questions. What are and what are used DRLs?.

Response: Thank you for this comment. As mentioned in our methodology (Data Collection), and revised in this re-submission for better clarity.

‘Data were extracted from the hospital radiological information systems. Using Monte Carlo calculation software^*, CT exposure parameters (e.g., DRLs) including CTDIvol (mGy), DLP (mGy.cm), and effective dose (ED) in millisieverts (mSv) were obtained and verified using the cloud-based Teamplay™ (Siemens Healthineers, Er-langen, Germany) data management software^**.’

^{*Williams G, Zankl M, Abmayr W, Veit R, Drexler G. The calculation of dose from external photon exposures using reference and realistic human phantoms and Monte Carlo methods. Physics in medicine and biology. 1986;31(4):449-52.}

^{**Annelinde Veen. Teamplay – Streamline Clinical Operations to Unlock Productivity Gains. Siemens Healthineers, Erlangen, Germany|2020-04-14 Available from: https://www.magnetomworld.siemens-healthineers.com/clinical-corner/case-studies/teamplay-streamline-clinical-operations.html. Accessed September 22, 2022.}

Kindly consider the revisions made in this version.

80. Lines 54 to 80. Delete the acronyms that are not repeated at least 3 times throughout the entire text. Check AEC, ATCM, ALARA KSA.

Response: In this re-submission, we made sure to omit all these acronyms accordingly.

75. Line 75. Because it talks about exposure indices and not quantities?. I suggest checking and adding bibliographic reference ICRU 2005 Patient dosimetry for x rays used in medical imaging ICRU Report 74 J.

(Bethesda, MD:International Commission on Radiological Units and Measurements)

Response: Thank you for this comment. Since the scope of our study is related to Computed Tomography imaging, we found out after reviewing the aforementioned reference that it is not suitable to be included from the author’s perspective. However, the term ‘indices’ has been replaced by the term ‘quantities’ throughout the manuscript to address the suggestion from the respectable reviewer.  

Materials and Methods:

1. Page 3.
2. Line 83. Please add a bibliographical reference to support the research design used.

Response: I am very grateful to you for pointing this out; these sentences have been added to the methods part to consolidate our study design scientific merit:

‘Retrospective retrieving and prospective registering of data by utilizing a software was conducted before and after radiation exposure via CT imaging. Comparative ambispective/ambidirectional design with a fixed interval (e.g., 1.5 years before and 1.5 years after optimization of dose measures) has reasonable scientific merit for studying the impact of dose optimization across time.^*,**’

^{*Lazcano G, Papuzinski C, Madrid E, Arancibia M. General concepts in biostatistics and clinical epidemiology: observational studies with cohort design. Medwave. 2019 Dec 16;19(11):e7748. Spanish, English. doi: 10.5867/medwave.2019.11.7748. PMID: 31999676.}

^{**Commenges D, Moreau T. Comparative efficiency of a survival‐based case‐control design and a random selection cohort design. Stat Med. 1991;10(11):1775–1782.}

Kindly consider the revisions made in this version.

93. Line 93. Could you explain in more detail how many patients were grouped into the pre-optimization and post-optimization groups and what were the criteria used?.

Response: Thank you for this comment. The following sentences have been added to the methods to address this point clearly for the respectable reviewer and readers.

‘The rationale behind the ambispective design in this study was that the study patients were divided into two equal groups to study the impact of the optimization effect on radiation doses: A) pre-optimization phase (1500 patients); those imaged on or before June 1, 2021 (January 1, 2019, to June 30, 2020 [1.5 y]) and B) post-optimization phase (1500 patients); those imaged after June 30, 2020 (July 1 to December 30, 2021 [1.5 years]).’

Kindly consider the revisions made in this version.

• Also, when optimization procedures are performed, the diagnostic quality of the images should be evaluated. In this case, explain how this point was addressed in the study.

Response: Thank you for this comment. In medical imaging, national Diagnostic Reference Levels guide physicians in managing radiation doses while maintaining good imaging quality. In 1996, the International Commission on Radiological Protection (ICRP) established diagnostic reference levels (DRLs) as benchmarks for identifying abnormally high radiation doses and optimizing radiation protection and image quality.^*,**

This study focused merely on optimizing radiation protection in CT imaging. This was implicated by reducing the radiation doses to the patients and their exposed organs, enabling us to correlate with NDRLs in the KSA^*** , and adhere to international guidelines of radiation exposure. It did not assess the image quality which is beyond the scope, and has now added to our study limitation in this re-submission. 

‘Finally, this study did not assess image quality, which was beyond the scope of our study.’

However, quality control of ionizing radiation exposure was extensively explored in this study based on references from the Saudi Food and Drug Authority (SFDA) recently established the National Diagnostic Reference Level measured by CTDI and DLP.^***

^{*European Commission, Food and Agriculture Organization of the United Nations, International Atomic Energy Agency, International Labour Organization, OECD Nuclear Energy Agency, Pan American Health Organization, United Nations Environment Programme, World Health Organization, Radiation Protection and Safety of Radiation Sources: International Basic Safety Standards: General Safety Requirements Part 3, No. GSR Part 3, IAEA, Vienna (2014).}

^{**International Atomic Energy Agency (IAEA). Radiation Protection and Safety in Medical Uses of Ionizing Radiation, IAEA Safety Standards Series No. SSG-46, IAEA, Vienna (2018).}

^{*** Saudi Food and Drug Authority: Medical Devices Sector. National Diagnostic Reference Levels (NDRL) Computed Tomography (CT) – Adult; 2021. Available from: https://sfda.gov.sa/sites/default/files/2020-08/%28NDRL%29En.pdf. Accessed April 30, 2022.}

Kindly consider the revisions made in this version.

105. Line 105. Please explain the Quality Assurance Program of the Medical Physics Department in your service. Detail the quality tests and the quality control process, must mention the performance testing in done regularly done and as dose metrics are verified regularly.

Response: The QA is done by a subcontract company specialized in medical physics. Yes, it is being performed regularly (yearly). The assessment include the following: Radiation Safety, Radiation indicators and warnings present and functional, Appropriate radiation shields present and functional, CT Unit Assembly Evaluation, Mechanical motion and locks of table functioning correctly, Gantry tilting motion functional, Alignment lasers accurate, CT Number Scale Assessment, CT number scale accuracy, High Contrast Resolution Assessment, Limiting resolution acceptable, Low Contrast Detectability Assessment

Limiting low contrast acceptable, Noise Level Assessment, Noise level, CT # Uniformity & Artifacts Assessment, CT# uniformity, Image is free of artifact, Slice Thickness Accuracy, Slice thickness within the acceptable limit, Radiation Dosimetry.

Herein, we attach some of the reports for the respectable reviewer: https://drive.google.com/file/d/1RyqpV0FhcU6yzVeKSRK75uiCQr5eUs9z/view?usp=share_link

113. Line 113. You must review and correct the writing of the Computed Tomography Dose Index quantities, since the acronym was previously defined.

Response: Thank you for your comment. This has been amended accordingly in this re-submission.

2. Page 4.
3. Line 117. Why do you write? DLP Milligray Centimeter (mGy.cm)….

Response: Thank you for your comment. This was to show the used unit in measuring DLP in this study. However, to avoid ambiguity, this has been amended accordingly.

118. Line 118. You should adding bibliography reference at the end of the sentence. DLP is directly related to patient risk from absorbed dose received

Response: Thank you for your comment. This has been amended accordingly in this re-submission.

129. Line 129. Please explain in more detail how many patients were used in the group

Response: Thank you for this comment. The following sentences have been added to the methods to address this point clearly for the respectable reviewer and readers.

‘The rationale behind the ambispective design in this study was that the study patients were divided into two equal groups to study the impact of the optimization effect on radiation doses: A) pre-optimization phase (1500 patients); those imaged on or before June 1, 2021 (January 1, 2019, to June 30, 2020 [1.5 y]) and B) post-optimization phase (1500 patients); those imaged after June 30, 2020 (July 1 to December 30, 2021 [1.5 years]).’

Kindly consider the revisions made in this version.

130. Line 130. Why do you talk about machines, if I only use a tomography equipment? Clarify.

Response: Thank you for this comment. In medical imaging, it is acceptable to call the CT scanner a machine because it works by machinery rotation inside its gantry. However, to avoid ambiguity, the term ‘machines’ has been replaced with ‘equipments’ in this revision.  

Results:

1. Page 6.
2. Line X. I do not understand at the end of table 1 the p-values. Please can you explain what you are comparing?.

Response: I am very grateful to you for pointing this out; we are comparing dose quantities in the pre-optimization phase with post- optimization phase using an unpaired t-test of independence for comparison. Accordingly, this was added to the footnote for better clarity.

‘՟ Statistical tests were conducted at a significance level of 0.05. Comparison of the pre-optimization phase with the post-optimization phase using an unpaired t-test of independence’

2. Page 7.
3. Line X. In table 2 you write Diagnostic Level Product, but must say dose–length product.

Response: Thank you for this valuable comment. Yes, we agree with the reviewer and Table 2 was revised and amended accordingly.

2. Line X. According to the ICRP recommendations (135 report), the effective dose magnitude should not be used to establish DRLs, therefore, omit this comparison from Table 2.

Response: Thank you for this valuable comment. Yes, we agree with the reviewer and Table 2 was revised and amended accordingly.

1. Line X. In table 3, explain what was the criteria for reporting the doses in some organs only. Also explain if the dose to the breasts was for all patients or only women.

Response: Due to our selection of the most sensitive organs. And, indeed, the breasts dose was for women only.

Discussion:

1. Page 7.
2. Line X. You must worry about naming all the tables of the results section.

Response: Thank you for this valuable comment. In this re-submission, all Tables are called out in their related place within the discussion.

Conslusion:

1. Page 10.
2. Line 324 It should be expanded and answer all your objects proposed.

Response: Thank you for your valuable comments. The conclusion has been revised and clearly presents our answers to the research question in this re-submission.

 

In this version, we have revised the paper’s message, and with the help of your constructive comments, We were able to convey the study's aim and findings to the reader. Further, we was able to improve the description of our method to ensure its clarity and reproducibility. Our final results are scientifically sound and of plausible strength. Kindly consider the improvements that have been made in this version.

 

We have incorporated the changes suggested by the second reviewer in the revised manuscript. We hope that we have adequately addressed all the issues raised and that our manuscript is now suitable for publication in applied sciences.

Author Response File: Author Response.docx

Reviewer 3 Report

General comments

The paper by  Al-Othman et al. is interesting and well written; authors provide an interesting study on CT imaging dose optimization through the identification of protocols that allow a dose reduction and the definition of institutional DRLs as a benchmark that would enable them to correlate with NDRLs in the Kingdom of Saudi Arabia. The study design and the patients cohort are very adequate.

The cited literature is up-to-date, however it could be improved by citing recent studies made in other countries, such as Italy, e.g.:

Compagnone, G., Padovani, R., D’Ercole, L. et al. Provision of Italian diagnostic reference levels for diagnostic and interventional radiology. Radiol med 126, 99–105 (2021). https://doi.org/10.1007/s11547-020-01165-3

For the definition of the DRLs It would have been desirable to have a prospective study and to take into account the data of the patient's weight; however, the authors emphasize this point in the section Research Limitations.

Some minor corrections are needed as indicated in the specific comments; in particular, measurement units should be added in particular in the Tables.

In my opinion, the paper by Al-Othman is of interest for Applied Science, and should be accepted after minor revisions.

 

Specific Comments

All text : for the sake of clarity, when the cited reference is at the end of the sentence, please move the full stop after the bracket.
E.g. line 40: “…tool in medical practice [1,2].” instead of “…tool in medical practice. [1,2]”

Line 32: Siemens instead of Siemen

Result section

For the sake of clarity, please add the measurement unit for CT exposure parameters when cited, in particular in Table 1, Table 2  and Table 3 column headings (e.g. ED (mSv); etc.)

Table 2: subheading Diagnostic Level Product stands for? Same of  DLP -Dose Length Product? Please clarify.

Comments for author File: Comments.pdf

Author Response

Reviewer 3

General comments

The paper by Al-Othman et al. is interesting and well written; authors provide an interesting study on CT

imaging dose optimization through the identification of protocols that allow a dose reduction and the

definition of institutional DRLs as a benchmark that would enable them to correlate with NDRLs in the

Kingdom of Saudi Arabia. The study design and the patients cohort are very adequate.

Response: Thank you.

The cited literature is up-to-date, however it could be improved by citing recent studies made in other

countries, such as Italy, e.g.:

Compagnone, G., Padovani, R., D’Ercole, L. et al. Provision of Italian diagnostic reference levels for diagnostic

and interventional radiology. Radiol med 126, 99–105 (2021). https://doi.org/10.1007/s11547-020-01165-3

Response: Thank you very much for bringing this study to the authors' attention; the Compagnone et al.^* study has been added to (Table 2) illustrating the comparison between our study and other international studies. Also, our Discussion section has been modified accordingly.

^{* Compagnone G, Padovani R, D'Ercole L, Orlacchio A, Bernardi G, D'Avanzo MA, Grande S, Palma A, Campanella F, Rosi A. Provision of Italian diagnostic reference levels for diagnostic and interventional radiology. Radiol Med. 2021 Jan;126(1):99-105. doi: 10.1007/s11547-020-01165-3. Epub 2020 Apr 1. PMID: 32239471.}

For the definition of the DRLs It would have been desirable to have a prospective study and to take into

account the data of the patient's weight; however, the authors emphasize this point in the section Research Limitations.

Response: Thank you for this valuable comment. Yes, we agree with the reviewer, and we regret that this was one of our identified study limitations.

‘Second, the cohort was limited by the fact that the data monitoring system only rec-orded the patient’s body mass index, and the exact weight of a patient was missing. Patient weight (kg) is a key indicator of the size of a patient in medical imaging and it affects the DRL values of the research.’

Kindly consider the revisions made in this version.

Some minor corrections are needed as indicated in the specific comments; in particular, measurement units

should be added in particular in the Tables.

Response: Thank you for this valuable comment. In this resubmission, all tables were reviewed and amended accordingly. Further, we have added footnotes to Tables to clarify used statistics, units and abbreviations.

In my opinion, the paper by Al-Othman is of interest for Applied Science, and should be accepted after minor

revisions.

Response:

Dear respectable reviewer,

Thank you for your positive opinion about our study. We truly appreciate these words!

Specific Comments

All text : for the sake of clarity, when the cited reference is at the end of the sentence, please move the full

stop after the bracket.

E.g. line 40: “…tool in medical practice [1,2].” instead of “…tool in medical practice. [1,2]”

Response: Thank you for this valuable comment. This has been amended accordingly in this re-submission.

Line 32: Siemens instead of Siemen

Response: Thank you; this comment has been addressed accordingly in this re-submission. The typo ‘Siemen’s’ was corrected to ‘Siemens’.

Result section

For the sake of clarity, please add the measurement unit for CT exposure parameters when cited, in particular

in Table 1, Table 2 and Table 3 column headings (e.g. ED (mSv); etc.)

Response: Thank you for this valuable comment. In this resubmission, all tables were reviewed and amended accordingly.

Further, we have added footnotes to Tables to clarify used statistics, units and abbreviations.

 

Table 2: subheading Diagnostic Level Product stands for? Same of DLP -Dose Length Product? Please clarify.

Response: Thank you for this valuable comment. Yes, we agree with the reviewer and Table 2 was revised and amended accordingly.

 

We have incorporated the changes suggested by the third reviewer in the revised manuscript. We hope that we have adequately addressed all the issues raised and that our manuscript is now suitable for publication by applied sciences.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments for author File: Comments.pdf