Relationships of Radiation Dose Indices with Body Size Indices in Adult Body Computed Tomography
Round 1
Reviewer 1 Report
The paper investigated the relationships between radiation dose indices and various body size indices based on the CT data of 3,200 patients with 4 different CT scanners. The study indicated a simple and practical way to manage dose control in CT examination by considering the weight/height and weight of patients.
It is suggested to add a paragraph on the physical definition and mathematical expression of CTDI, CTDIvol, DLP and their relationship with effective dose E in section 2.
How to define the image quality of CT? Is the image quality the same for all the 3,200 patients with different CT scanners? CT examination seeks to achieve required image quality at the lowest exposure dose as possible.
The relationship between CTDIvol of different CT and parameters such as patient height and weight is different. What is the reason? Is the image quality of different CT scanners different, or is the image quality the same but the dose control method is different?
Is the volume or mass of human tissues and organs linear with height and weight itself?
The effective dose is the most direct physical quantity for the radiation risk assessment of CT examination. It is better if the effective dose of patients could be calculated with the CTDIvol, DLP and other data.
Author Response
Comment 1)
It is suggested to add a paragraph on the physical definition and mathematical expression of CTDI, CTDIvol, DLP and their relationship with effective dose E in section 2.
Reply 1)
We added explanation of imaging parameters used for CTDIvol calculation and description about the relationship between DLP and effective dose as follows (the first paragraph of Introduction):
“imaging parameters such as tube current, rotation time, and pitch”
“Effective dose, representing the risk of stochastic effects such as cancer induction and hereditary effects, may be calculated by multiplying DLP by an appropriate conversion factor [4].”
As for the physical definition and mathematical expression of CTDI, CTDIvol, and DLP, we added citation of AAPM report No.111 describing these parameters in detail.
Comment 2)
How to define the image quality of CT? Is the image quality the same for all the 3,200 patients with different CT scanners? CT examination seeks to achieve required image quality at the lowest exposure dose as possible.
Reply 2)
We agree about the importance of image quality in optimization and described the lack of systematic evaluation of image quality as the primary limitation in the original manuscript.
We added the following sentence:
“Investigation of dose-size relationships combined with image quality evaluation remains to be done.”
Comment 3)
The relationship between CTDIvol of different CT and parameters such as patient height and weight is different. What is the reason? Is the image quality of different CT scanners different, or is the image quality the same but the dose control method is different?
Reply 3)
The dose control method is fundamentally different between the Siemens scanner and the other three scanners. We revised the third paragraph of Discussion as follows:
“AEC systems in the GE and Fujifilm scanners modulate tube current to keep the noise level of CT images reconstructed by the standard method. For the Siemens scanner, the degree of increase in tube current with increasing attenuation is selectable and adjusted by the modulation strength [14,15].”
Comment 4)
Is the volume or mass of human tissues and organs linear with height and weight itself?
Reply 4)
The relationship between the sizes of tissues and organs and the body size represented by height and weight would be variable and non-linear.
Comment 5)
The effective dose is the most direct physical quantity for the radiation risk assessment of CT examination. It is better if the effective dose of patients could be calculated with the CTDIvol, DLP and other data.
Reply 5)
As stated in Reply 1, we added description related to effective dose.
The conversion factor used commonly is 0.014 mSv/mGy/cm for thoracic CT and 0.015 mSv/mGy/cm for abdominal, abdominopelvic, and thoraco-abdominopelvic CT. Therefore, calculated effective dose is almost proportional to DLP in adult body CT.
Reviewer 2 Report
This is a study of the relationship between body size and CT dose quantities, including CTDI, DLP, and diameter.
The article is clear and well written, so there is little left to add in that regard.
The relationship between CTDI and body size is intuitive and unsurprising, but it has not yet been so thoroughly investigated and described to such a high level of precision using a very wide set of patients before. Furthermore, the correlations with individual body size parameters like height, weight, BMI, etc... can instruct how which measurements are needed to best estimate CT dose for individual patients.
I would suggest to summarize Table 1 and 2 correlation coefficients using an average +/- 2 SD for each column and/or row. Otherwise, comparisons between scans, scanners, or body size indices are difficult to perform.
Additionally, I am unsure of the interest in correlating DLP to body size. DLP is simply a product of the CTDI and scan length, and will differ based on the anatomy of the patient. As the authors note, "variations in scan length in patients with the same attenuation strength appear to weaken the correlation between these indices and DLP".
Presumably, an investigator meaning to obtain an individualized risk estimate for a specific patient would be able to estimate CTDI (which is more closely related to body size) based on the patient metrics, and then use the length of scan actually used to scan the patient.
Specific comments:
L63: citation error (0-23)
L85-87: 200 patients x 4 scanners x 4 scans = 3200 - do you mean 3200 scans rather than 3200 patients? otherwise this is contradictory with the previously described 200 patients enrolled.
Author Response
Comment 1)
I would suggest to summarize Table 1 and 2 correlation coefficients using an average +/- 2 SD for each column and/or row. Otherwise, comparisons between scans, scanners, or body size indices are difficult to perform.
Reply 1)
We added means and SDs to aid comparison between scan regions, scanners, and body size indices.
Comment 2)
Additionally, I am unsure of the interest in correlating DLP to body size. DLP is simply a product of the CTDI and scan length, and will differ based on the anatomy of the patient. As the authors note, "variations in scan length in patients with the same attenuation strength appear to weaken the correlation between these indices and DLP".
Presumably, an investigator meaning to obtain an individualized risk estimate for a specific patient would be able to estimate CTDI (which is more closely related to body size) based on the patient metrics, and then use the length of scan actually used to scan the patient.
Reply 2)
As indicated by the reviewer, we can use the combination of CTDIvol and scan length, instead of that of CTDIvol and DLP, to assess radiation dose in a single imaging series. However, one examination may include two or more series for different scan ranges and different dose settings. In this case, the total DLP is preferable to assess the risk derived from the examination. Use of CTDIvol and DLP is recommended for radiation dose monitoring, and CT scanners provide dose reports showing these values for each examination.
Comment 3)
L63: citation error (0-23)
Reply 3)
We are sorry for the mistake. We corrected.
Comment 4)
L85-87: 200 patients x 4 scanners x 4 scans = 3200 - do you mean 3200 scans rather than 3200 patients? otherwise this is contradictory with the previously described 200 patients enrolled.
Reply 4)
The patients were different depending on the scanner and scan region.
The term “scans” is better than “patients”, and we corrected the description about the subjects (Abstract, 2.1. Subjects).
Reviewer 3 Report
The paper presents a significantly large set of data (number of patients and CT studies), grouped in 4 widely available CT scan types. It also includes CT studies for different regions of the body. The authors correlated patient dose indexes to two different types of indicators: based on body related physical measurements and based on images parameters (from the interaction of the radiation with the matter).
The results provide a very comprehensive amount of information. The methodology presented could be useful to other scientists in the area of x-ray diagnostic dosimetry, for the validation of their quality and dose management protocols. Ultimately those will contribute to the reduction of the dose levels to individual patients and the population, while keeping the quality of the image and therefore the quality of the diagnosis.
The article is in general well written, the sections are well structured, and the tables and figures are a good complement to the text. The references used are significant to the content of the paper.
The paper is using a significant amount of accumulated and relevant patient data to correlate physical information to the amount of radiation dose potentially received by patients during diagnostic CT procedures, which are expressed in terms of radiation dose indices (CTDIvol and DLP)
While the approach is not necessarily original, is definitely relevant. International efforts are aiming to the standardization of imaging acquisition protocols and diagnostic Radiation Dose Indexes, with the aim of reducing to the most affordable limit of dose to the patient, without compromising the quality of the images. However, every population has its own characteristics also each manufacturing implements the protocols in a bespoke manner. In my opinion, the data the authors analysed have both, a significant number of patients and different CT manufacturers. In that manner this research will contribute to reduce the gap in terms of the information required in support of standardization.
I believe that in the context of this, the correct word to use should be indexes instead of indices but I supposed that is for the editors to decide.
It adds information that is specific to the adult Japanese population and in relation the imaging procedures that are performed in the radiology centres in Japan, with the CT from the manufacturers that are available in Japan. That does not mean that procedures are perform in different way that to the rest of the world. It adds information to what other countries are doing in terms to stablished the Diagnostic Reference Levels (DRLs) in medical imaging according to the recommendations from international organizations.
The authors identified the limitations of their study. Certainly, the published information could be the bases for another investigation that will correlate it more directly to the quality of the image.
In my opinion, the conclusions are appropriated and also indicative of difference in the outcomes according the CT manufacturer. The conclusions are concise but consistent with their findings
The use of references is appropriated to the performed investigation, it includes relevant paper and also recently published ones.
The graphs and tables are a vey good complement to the text and provide information relevant for the understanding of the results.
Author Response
Comment 1)
It adds information that is specific to the adult Japanese population and in relation the imaging procedures that are performed in the radiology centres in Japan, with the CT from the manufacturers that are available in Japan. That does not mean that procedures are perform in different way that to the rest of the world. It adds information to what other countries are doing in terms to stablished the Diagnostic Reference Levels (DRLs) in medical imaging according to the recommendations from international organizations.
Reply 1)
We added the following statement to the last paragraph of Discussion about the study limitation:
“Data used in this study were obtained from Japanese patients. The size and shape of the body would differ among countries, and evaluation in other counties is desired.”
Comment 2)
The authors identified the limitations of their study. Certainly, the published information could be the bases for another investigation that will correlate it more directly to the quality of the image.
Reply 2)
We added the following statement to the last paragraph of Discussion about the study limitation:
“Investigation of dose-size relationships combined with image quality evaluation remains to be done.”
