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.

Thank you for submitting your question to AAPM Ask the Expert. Your desire to know your child’s “exact effective dose” from a diagnostic imaging exam is quite understandable. Effective dose is related to the risk of radiation-induced stochastic (related to probability) effects such as carcinogenesis, and in most cases that risk is what we would really like to know. I hope to explain why the effective dose to an individual from an imaging exam cannot be determined accurately, nor can we state with certainty what the stochastic risk is from an imaging exam.

“Effective dose” was originally intended for setting dose limits for radiation workers and others exposed to whole-body radiation. It was not originally intended to characterize the dose and risk from medical exposures, but over time it has been used that way. To determine effective dose for partial-body exposures (such as those from medical imaging), a weighted average of the contributing organ and tissue doses is calculated using tissue weighting factors that reflect how sensitive different organs and tissues are to radiation damage. The effective dose calculated in this way is related to the total radiation “detriment”, a measure of the health impact of stochastic effects such as cancer whose probability of occurrence increases with radiation dose.

A calculation of effective dose is only as good as the tissue weighting factors used in the calculation. Tissue weighting factors have been published by the International Commission on Radiological Protection (ICRP). The published factors are based on epidemiological studies of lifetime cancer risk from radiation exposures. The primary data set for these studies is the Japanese atomic bomb survivor cohort. This cohort is quite unique. The type of radiation exposure received by the study cohort was much different from the types typically used in modern medical imaging. The study included men and women of all ages, and almost all were of Japanese descent. The published weighting factors derived from these studies are not broken down by gender or age even though there is evidence that risk differences exist between males and females, and there is a risk dependence on age at time of exposure (higher risk at younger age). Despite this, ICRP published just one set of tissue weighting factors that is averaged over all members of the study populations. That is the main reason why effective dose cannot be determined for a medical imaging exam of an individual – the correct tissue weighting factors for an individual are not known. The best we can do is apply the “generic” tissue weighting factors for a “reference human” (a standardized adult human model), with the caveat that there is a high degree of uncertainty in the calculation. It has been suggested that numerical estimates of cancer risk based on effective dose could vary by one or two orders magnitude because of the uncertainty in the factors that go into the calculation.

Regarding your child’s digital radiograph of the spine, you stated that the important technical parameters that could have been used to determine the “entrance skin dose” or “incident air kerma” of the exam are not available. Entrance skin dose (ESD) or incident air kerma (IAK) is one way to characterize the dose from a radiographic exposure. Dose Area Product (DAP) or Kerma Area Product (KAP) is another. If we knew the entrance skin dose and the approximate size (thickness) of your child at the time of the exam, then we would be able to use those factors as inputs to a “Monte Carlo” computer simulation that models radiation transport and dose distributions. Such a program can calculate approximate organ doses and estimate effective dose (with the above caveat about the reference human). Without the specific technical parameters of your child’s exam, we can instead use common values for children of the same age with some confidence because there is not very much variation in these parameters for young children. Monte Carlo simulations have been performed and published in the scientific literature using common exposure parameters for “average-sized” adults. The table from the Health Physics Society that you cited (https://hps.org/hpspublications/articles/dosesfrommedicalradiation.html) is one example. It can be difficult to find similar data for children, but this recent publication (open access) tabulates approximate effective doses for common pediatric radiography exams, broken down by patient weight https://pubmed.ncbi.nlm.nih.gov/36453696/. See the dose chart in Fig 1. This table contains probably the best available estimate of your child’s effective dose from their imaging exam.

Exposure Index (EI is a measure of the average radiation received by the imaging detector in a digital radiograph. The radiation dose received by the detector comes from the “remnant beam”, which is the radiation that has transmitted through the patient. The goal in radiography is for the remnant beam intensity to be about the same for all patients, regardless of patient size, shape, age, etc. even though the entrance beam intensity will be much different between patients. To evaluate a patient’s dose, the entrance beam intensity (ESD/IAK) is needed, not the remnant beam. Therefore, the EI value is not helpful for patient dosimetry. EI is used to judge the technical quality of a radiographic examination, not the patient’s radiation dose.

Stochastic risk from medical radiation exposures is another area with considerable uncertainty. The radiation dose level above which there is direct epidemiological evidence of stochastic harm (excess cases of cancer) is about 100 mSv. Below this level the risks are less certain, and modelling must be used to calculate a “theoretical risk”. The most commonly accepted model is the “linear non-threshold” model, which assumes that risks at high doses extend linearly (proportionally) down to low doses, all the way to zero dose. Using this model, a lifetime fatal cancer risk coefficient of 5% per Sv is recommended by the ICRP. This corresponds to 1 fatal cancer per 20,000 patients receiving 1 mSv. Medical imaging radiation exposures span a range of 0.001 – 25 mSv effective dose, which is below the level where there is direct evidence of increased harm. Therefore, the risk associated with any medical imaging exposure is purely theoretical, in most cases is extremely small, and may in fact be zero. It is worth noting that all living things receive about 3 mSv per year from radiation sources that exist naturally on earth.

The basic principles of radiation protection in medicine are justification and optimization. Justification means that the radiation exposure must show a sufficient net benefit when balanced against possible detriments that the exam might cause. Optimization means that the technical parameters used for the exam have been selected to obtain the necessary diagnostic information with the lowest possible radiation dose. Medical practitioners are trained to ensure that justification and optimization are used in all radiological examinations. Because of the theoretical risks from low doses, all radiation users are trained to follow the “ALARA” principle: keep radiation exposures As Low As Reasonably Achievable.

In almost all cases, the proven benefits of medical imaging outweigh the small theoretical (not proven) risks from exposure to low radiation doses. https://imagegently.org/ is a great resource for information about radiation in pediatric imaging. It contains some limited information about typical effective doses from some common radiological procedures.

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