Hello, If I understand the American Association of Physicists in Medicine (AAPM) report 293 correctly, the SSDE and CTDIvol values for children are approximately the same. This is because, as I understand it, the fH16 factor (conversion factor) is quite small even for newborn infants (e.g. between 0.9 and 1.05 for a one-year-old child). In fact, for children older than 1 year, the fH16 value becomes smaller and therefore the SSDE value also becomes smaller. This means, for example, that the CDTIvol value shown in the dose report of a 3-year-old child after a CT scan should actually be smaller. Please allow me to ask 4 questions about all this: 1- Is my summary above correct? 3- Is this formula correct to convert CDTIvol to SSDE? SSDE= fH16*CTDVol 3- How can I convert SSDE value to effective dose? 4- When we calculate with the conversion factors in the AAPM 204 report, sometimes there is a big difference between SSDE and CDTIvol, why do the conversion factors in the AAPM 293 report do not cause a big difference between SSDE and CTDIvol? Yours sincerely.

SSDE is not the same thing as CTDIvol. CTDIvol is a measure of a CT scanner’s radiation output, and does not represent a patient’s absorbed radiation dose. SSDE is an estimate of patient absorbed dose and is determined by applying a multiplicative conversion factor (a scaling factor) to the CTDIvol value reported by the scanner for a given examination. Conversion factors have been published in AAPM reports 204 (for body imaging) and 293 (for head imaging).

1. Your summary is mostly correct, but the CTDIvol that is generated by the scanner and shown in the dose report can be assumed to be correct. The accuracy of the reported CTDIvol is checked regularly by an independent medical physicist. CTDIvol is a measure of the scanner’s output, not what the patient absorbed. It is SSDE, not CTDIvol, that accounts for the patient size. For a 3 y.o. child, the conversion factor is less than 1 and therefore the SSDE is smaller than the CTDIvol.

2. Yes, the formula (Eq 2c on page 19 of AAPM Report 293) is correct.

3. You cannot convert SSDE to effective dose. See the last sentence of the Summary on page 19 of AAPM Report 293, and Recommendation #3 also on page 19. Effective dose cannot be determined accurately for individual patients. SSDE does not take into consideration which organs received radiation or the length of the scan.

4. The wider range of conversions factors for body imaging (the subject of AAPM Report 204) compared with head imaging (AAPM Report 293) is a reflection of the wider range of size (effective diameter, water-equivalent diameter), and therefore x-ray attenuation. Small objects (like heads) have a more uniform dose distribution than large objects (like the abdomens of larger patients), where peripheral anatomy acts as a “shield” and reduces the dose to locations deeper into the body. The conversion factor accounts for this uneven distribution of dose and produces an SSDE that reflects the average absorbed dose across the object.

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Hello, I want to calculate how much effective dose my child (6 months old, male) received as a result of a computed radiography scan he had in 2016. On the image, it is written “Stitching Spine AP”, however the image looks like a Pelvis scan actually. There is not much information in the DICOM outputs after the scan unfortunately, so I do not have kVp, mAs, grid, SID, filtration, beam collimation, DAP, ESD etc. information. But I saw in an article on the internet that the “exposure index (EI)” value is a parameter that can give an idea about the patient dose. I am copying the article link below: https://www.sciencedirect.com/science/article/pii/S107881742030050X The brand of the CR device on which the scan was performed is Konica Minolta (manufacturer model name: 0817 and station name: CS-2). In the DICOM outputs, the value of tag 0018,1405 (relative x-ray exposure) is given as 130. The value for tag 0018,6000 (sensitivity) is given as 250. As I understand from below links, these are the manufacturer-specific units of radiation dose measured on the detector (or imaging plate): https://dicomlookup.com/dicomtags/(0018,1405) https://www.dicomlookup.com/dicomtags/(0018,6000) I thought these were the tags I should focus on, and I tried to find radiation values corresponding to these units on the internet. I found an article which shows that the value of 130 in tag 0018,1405 for Konica Minolta corresponds to a rough estimate of 20μGy (0.02 mGy) of detector exposure. Article link is below, shown on table 2: https://pmc.ncbi.nlm.nih.gov/articles/PMC3076558/ As I understand it, this value is the value absorbed by the detector, not by patient. However, assuming that the patient dose would be similar, I tried to calculate the equivalent dose, and by setting the radiation weighting factor (Wr) to 1 (since it is X-ray), I calculated the equivalent dose as 0.02 mSv. For effective dose, organ/tissue factor comes into play, as far as I have read, each tissue has different weight factors, and the sum of these factors for the whole body is “1”. I saw on a website (link below) that the tissue weight factor for bone-marrow (red), colon, lung, stomach, breast, remaining tissues is a value like “0.72”. https://ec.europa.eu/health/scientific_committees/opinions_layman/security-scanners/en/figtableboxes/tissue-weighting-factors.htm Therefore, I calculated the total effective dose of my child as 0.02×0.72=0.014 mSv. My specific questions are as follows, I would be very happy if you could answer them: 1- Is there a place where I can officially find the exposure index values of Konica Minolta CR device? I heard that there is information on this subject in AAPM TG116, but I couldn’t find it. Here is the link: https://www.aapm.org/pubs/reports/RPT_116.pdf 2- I don’t think it would be right to calculate my child’s effective dose from the absorbed dose on the detector, but considering the thickness of a 6-month-old child, I guess there won’t be a big difference between my child’s absorbed dose and the dose absorbed by the detector, what do you think? 3- I think that the patient’s age should also be taken into account when calculating the effective dose, but I don’t know how to add it to the calculation, and I can’t find any information on the internet about such a parameter being used for CR scans, what do you think? 4- Can the doses corresponding to the exposure index vary according to the calibration of the device? Does “calibration topic” make a big difference? 5- While the average effective dose for “pelvis” is given as 0.7 mSv on a table shown at hps.org website (https://hps.org/hpspublications/articles/dosesfrommedicalradiation.html), I believe that the value I calculated (0.014 mSv) for my 6-month-old child is not possible to be correct, what do you think? If my above calculation is wrong, may I kindly ask you to make corrections on my calculations step by step to make me understand better? Thank you very much for your time in advance. P.S. I don’t have a medical physics or medical education, I’m just an engineer trying to understand what I read and is very worried about my child, so I’m sorry if there are any fundamental mistakes in what I wrote.. Those I have contacted about this topic have always given me general answers based on literature data, but I would like to know the exact effective dose based on the actual numbers from my child’s scan, please help me. Wishing you all a healthy new year. Best regards.