The Use of Effective Dose as a Radiological Protection Quantity
5.0 Medical Exposures: no additional suggestions.
This section makes appropriate distinctions among CTDIvol, DLP and effective doses. Indicates that it is a useful reference value to use ED to compare among procedures that expose different regions of the body, but that it is not intended to provide estimates of risk to individual patients. Section also indicates that “effective risk” as advocated by some is too riddled with uncertainties at diagnostic levels to be useful for that purpose.
5.1 Effective dose from medical procedures: see below for edit suggestions/comments
This section makes it clear that ED refers to a reference person, not the individual patient. The authors make a point of indicating that the ED should be applied as a reference within the geographical context of the region and country, and include data on radiography, interventional CT and nuclear medicine procedures in the UK, USA and the Russian federation. The problems that with this are several:
1) The reference data from the US are estimates1 from a reference that was published in 2008, obviously utilizing older data, which was estimated from sources such as NEXT (National Exposure X-Ray Trends) from which information such as exposure factors in neonatal abdominal CT of kVp 120 and mAs 2402 were derived.
2) The reference data for the UK estimates is derived from a reference3 which in turns derives the data from a government publication from 2014.4 This however is based on a survey conducted in 2011, at a time when the respondents were using equipment that would now be ten years old, and was likely using filtered back projection for reconstructions.
It may be that these are the best data available, but when categorical statements regarding exposure to patients are made, these caveats should be clearly stated.
5.2 Justification of procedures: no additional edits.
This section speaks about three levels of justification, and I think is well put.
5.3. Optimisation and reporting of doses: see edit suggestions/comments below
This section discusses how ED can be used to choose a modality based on clinical need as balanced by radiation exposure. Lines 1703-1714. These describe the delta between a chest radiograph and a high dose chest CT; however, the delta between a chest radiograph and an optimized, much lower dose chest CT should also be described. It is not black and white.
The document also discusses differences in application of CTDIvol, specific organ dose and ED, use of ED in dose tracking, assessment of unintentional doses, and dose to carers.
5.4. Effective dose and risk communication: see edit suggestions/comments below
The authors indicate that although ED is not intended as a measure of risk to an individual, they indicate that use of ED as a surrogate or approximate indicator for risk in general terms with appropriate caveats can be useful. This includes Table 5.2 which discusses relative risks based on ED, with the risk labeled as inferred, or based on the LNT stochastic model.
Age, race, ethnicity and sex-specific cancer models are discussed and tables and graphs of total lifetime cancer risks are provided. The authors do indicate (lines 1882-1884 and 1890-1893) that the reliability of cancer estimates at low dose is not precise and is associated with “substantial uncertainties”. This information should be clearly noted in the legend of the Tables and graphs, not just buried in the text where it can be easily missed. REFERENCES
1. Mettler, F.A., Jr., et al. Medical radiation exposure in the U.S. in 2006: preliminary results. Health physics 95, 502-507 (2008).
2. Brenner, D.J. & Hall, E.J. Computed tomography--an increasing source of radiation exposure. The New England journal of medicine 357, 2277-2284 (2007).
3. Shrimpton, P.C., Jansen, J.T. & Harrison, J.D. Updated estimates of typical effective doses for common CT examinations in the UK following the 2011 national review. The British journal of radiology 89, 20150346 (2016).
4. Shrimpton, P.C., Hillier, M.C., Meeson, S. & Golding, S.J. Doses from computed tomography (CT) examinations in the UK --- 2011 review. (Chilton, UK: Public Health England, 2014).
Other comments:
general:
a. From med physics perspective it is difficult to endorse this report because it flies in the face physics training and understanding of effective dose. Being an advocate for pediatric radiation safety, it is difficult to see how this report in its current form helps to improve the current safety and care of the pediatric population.
b. We anticipate some very strong reactions to this report by the physics community although it may be welcomed by the general healthcare population.
c. In its current state, the broad and population-averaged application of effective dose really is a step away from "personalized healthcare".
d. The underlying limitations and weaknesses of E are buried in the text so as to be easily missed unless a reader reads every word and every page of this text.
e. There are inaccuracies involved in assuming one size patient and using a single model for all patients, large and small is perfectly acceptable. There is no attempt to quantify the increased inaccuracy for children in doing this. This all flies in the face of Image Gently''s premise that one size does not fit all.
1. Consider changing title to “The Use of Effective Dose as a Radiological Protection Quantity in Medical Exposure (as in P7, under L13)” 2. L49: A detriment should be with lower case “d” 3. L92: Add “ionizing” before radiation 4. L98: Before interventional procedures, would add image-guided (etc. throughout document) 5. L99: “the use of different techniques and technologies…” 6. L248: “few radionuclides or high exposure (e.g. accidental) of any radionuclide…” 7. L250: “set in effective dose applied to all…” 8. L255: (e.g. CT and nuclear medicine: these are not interventional imaging modalities. Are they put in the wrong place in the sentence? 9. L259: “risks to clinicians and patients as well as parents or other caregivers”. And this should be considered throughout the document that sometimes parents are in the room with children so discussion should not be limited to occupational exposure and patients alone. This is an important point in pediatric imaging. 10. L261: “…interventional procedures, as guidelines in research studies, …” 11. L262: E does not really provide a measure of detriment but a measure of potential for detriment. This is an important distinction. 12. L265: Would eliminate the word "iinitial" 13. L269: “variation in this in risk with age…” 14. L275: Diseases does not cover the spectrum of conditions for which imaging is performed. Diseases imply non-traumatic conditions. Consider disorder or medical condition. In fact, Oxford dictionary says a disease “is not a result of direct injury”. 15. L299: In addition, it… "It" is a misplaced modifier. Say E again. 16. L317: Represents its estimated and then contribution to total…
17. L334: “that may conceal differences…” 18. L337: “…2013”. For example 19. L337: “…of radiation induced thyroid cancer… 20. L334: eliminate "principally" that as already implied earlier in the sentence 21. L413: Add radiation-induced before impairment of organ/tissue 22. L652: The use of the word “spurious” implies that this is false or fake. Consider changing to “to avoid implication of high degree of accuracy” 23. L1304: Change "clinicians" to the word "individuals" 24. L1489: Should be 10 year old rather than 10 years old 25. L1607: “medical procedures as well as intrinsic biological susceptibility including genetic predisposition, …” 26. L1618: What is a non-specialist in radiological protection? Is this well understood? 27 L1639-1641: Clinical services would argue that daily decisions for justifying individual patient imaging exposures do not require approximate estimates of dose relating to inferred risks to health. This is in fact rarely if ever done. 28. L1680: Be careful when identifying radiologist that other imaging experts are considered as relevant or not such as cardiologists. 29. L1683-4: Again, the medical risks of a suspected disease is not often considered relative to some of the small risks (i.e. radiation) of getting an examination for that test. To say this “has to be considered" is an over statement and would be argued by most clinical providers. 30. L1692: “obtained for larger bodies of adults” 31: L1715-1742: In general, these are fairly strong statements about what goes into decisions (i.e. design, appropriate selection, construction of equipment, and installations). healathcare providers in fact do not follow these in their decision made regarding an imaging procedure but these considerations pre date this point of care decision. I believe this section needs to be reworded to more clearly define what steps and in what order various aspects of equipment design, manufacture, application, etc. are done. 32. L1719: How do techniques and procedure parameters differ? 33. 1720: Quality parameters need to be considered along with protective measures. 34. Table L1845: Is this for adults only? 35. L1850: Consider changing this title to age- and sex specific effective dose and cancer and associated cancer risk. 36: Table 5.3 Is AP, PA and lateral, head and AP and lateral cervical spine cancer risk for 0-9 year olds really the highest of all the modalities listed here? This seems doubtful.
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| Reviewer | Lines | Page | Comment | Suggested Edit |
| Medical Physicist 1 | 260-66 | 9 | E should not be used for justification or to inform decision for diagnostic imaging alone (radiation dose alone should not deter a practiner from choosing a clinically necessary/beneficial diagnostic test); the risk/benefit model should be employed for the diagnostic test. Skin dose should be used to inform decisions on how to treat/plan for IR procedures; peak skin dose would fall within the category of single radiosensitive organ (as explained on line 271). | This bullet should be removed |
| Medical Physicist 1 | 334--38 | 11-12 | This is a very important point, when dealing with the calculation of E for young populations (i.e. pediatrics), and should be emphasized. | It should be emphasized that wT coefficients were adapted to account for age risk, e.g., Thyroid assigned a higher weighting factor (0.04) than either adult values 0.021 (female) and 0.008 (male) because detriment to thyroid was determined to be greater when accounting for sensitivity to younger populations. also inclusion of this comment in the Main Points would be appropriate |
| Medical Physicist 1 | 339--42 | 12 | derivation of wT and risk coefficients are bounded by large error bars. | Comment on the magnitude of calculation error should be included. |
| Medical Physicist 1 | 349-50 | 12 | Hereditary effects have not been seen in humans. | It should be emphasized that hereditary effects have only been seen in animal models and not humans (hence the downgrade of wT for gonads). |
| Medical Physicist 2 | 489-90 | 15 | until true patient-specific dosimetry is achieved, along with reliable archival processes, the primary limitation of these studies will not be overcome, namely: the assumption of dose level. | Mention of SSDE as a means to better relate patient-specific dose from CT studies as an example of improved dosimetry should be considered. |
| Medical Physicist 2 | 935-946 | 28 | These lines discuss a significant point of confusion among radiologists with respect to patient dose since both H and E use the same unit of Sievert. | The text currently provides an excellent example of this dilemma for the thyroid when I-131 is administered. Please add an example for CT. I would suggest providing an estimate of the average organ dose of an adult liver for an abdominal/pelvic CT examination along with E dose. Finally, an example of digital radiography should be provided using the entrance skin dose for an adult lateral lumbar spine image along with the estimated E dose. |
| Medical Physicist 2 | 957-960 | 28 | Too many radiologists, and other users of E dose, do not have a reasonable appreciation for the large uncertainties associated with the estimate of E dose. | At the end of line 960 add: Due to the relatively large uncertainties in the estimate of E dose, e.g. wT and wR, estimates of E dose typically should not include more than one significant figure, two at most. |
| Medical Physicist 2 | 1036-1037 | 30 | The last sentence of this paragraph is extremely important with respect to improving the accuracy of estimates of E dose for children. | Please provide information of the expected date and where improved K-factors for pediatric E-dose estimates might be expected. |
| Medical Physicist 2 | 1186-1187 | 33 | As written, these last two sentences are confusing. So the commitmen period for adults is 50 years from time of exposure? Is the commitment. for children 70 years from the exposure or until the age of 70 as stated? Please clarify. | |
| Medical Physicist 2 | 1212-1213 | 34 | This last sentence is not helpful. A statement concerning the degree of uncertainty for estimates at the pediatric ages compared to the uncertainty for an adult estimate is needed. | |
| Medical Physicist 2 | 1253 | 35 | Statement is too strong | " . . . For management of occupational exposure . . ." |
| Medical Physicist 2 | 1255 | 35 | radiological protection, dose, image quality is never ''optimized''. This is misleading. All places in document where this word is used should be changed. | change ''optimization'' to ''management'' |
| Medical Physicist 2 | 1274 -1280 | 36 | This is extremely important point poorly understood by many. Sentence to right should be added. | ". . . below). However, effective dose cannot be estimated using generalised data and methods and then applied to an individual. |
| Medical Physicist 2 | 1300 | 36 | aprons cannot be purchased today constructed of ''lead/rubber" | "protective aprons constructed of attenuating materials with a lead equivalent thickness worn in radiology departments . . ." |
| Medical Physicist 2 | 1304 | 36 | Typo? | ". . . procedures should wear two . . ." |
| Medical Physicist 2 | 1495-1509 | 36 | The ''concern'' in the first line, which this paragraph seeks to dismiss, is a valid concern since this document states that children are more radio sensitive than adults. I understand the desire to have a single set of tissue weighting factors regardless of patient size because it is convenient. However, quality pediatric patient care is challenging and typically not convenient. A single set of tissue weighting factors is not "entirely appropriate" for children. At a minimum this paragraph should acknowledge that one set of tissue weighting factors may result in additional error in the estimation of effective dose for children and provide estimates of the magnitude of the additional error. | |
| Medical Physicist 2 | 1508-1509 | 40 | See previous box. Provided the changes that are requested in that box are added, the last sentence of the paragraph should be edited to provide the message indicated to the right. | ". . .individual basis. For practical radiation protection purposes, the use of a single set of tissue weighting factors may be appropriate provided one understands the typical increased errors in estimations for children described above." |
| Medical Physicist 2 | 1547-1550 | 41 | These four lines contain very important information that is poorly understood by many. These statements need to be amplified by providing a couple of general examples of relatively recent publications that have specifically violated these principles (numbers of additional cancers in the future caused by diagnostic x-ray examinations stated) because the reviewers for these journal articles did not understand the limitations of effective dose. This needs to change. | |
| Medical Physicist 2 | 1551-1564 | 41-42 | This information should be a separate paragraph. | |
| Medical Physicist 2 | 1621-1622 | 43 | An extremely important statement that needs to be amplified and clarified for too many practitioners in the medical field who do not understand limitations of E dose. | "applications and is inappropriate." |
| Medical Physicist 3 | 1634-1636 | 43 | While the report repeatedly presents that the differences between risk estimates based on effective dose are relatively small between different population subgroups, it never defines the threshold where differences would be large enough to require sub-population specific risk estimates. Additionally, the uncertainties for these risk estimates are discussed but never quantified. For example, because the pediatric population used for epidemiological studies is substantially smaller than the adult population, the uncertainties associated with carcinogenic risk are greater. | "… differences between estimates of risk based on effective dose…. are predictable and generally not large, although the associated uncertainties of risk may vary substantially." |
| Medical Physicist 2 | 1650-1651 | 43 | An extremely important statement that needs to be amplified and clarified for too many practitioners in the medical field who do not understand limitations of E dose. | |
| Medical Physicist 2 | 1661 | 44 | An extremely important statement that needs to be amplified and clarified for too many practitioners in the medical field who do not understand limitations of E dose. | ". . . breast, estimates of organ (mean glandular) dose should be used instead of effective dose. Likewise, during general radiography or CT examinations, estimates of organ or tissue dose that are irradiated by the direct beam of x-rays should be determined as opposed to effective dose. Similarly, . . " |
| Medical Physicist 2 | 1664-1667 | 44 | There is no justification for highlighting the gonadal dose compared to other organ doses within the abdomen such as the colon and stomach which have a greater tissue weighting factor per ICRP 103. See following: Medical Physicist 2 KJ, et.al. Reconsidering the value of gonadal shielding . . . J Am Coll Radiol. 2017 Dec;14(12):1635-6. | Delete existing lines |
| Medical Physicist 3 | 1691 | 45 | Because of the relative proximity of organs, as well as organ size, this statement should be strengthened. | "… dose distributions within the smaller bodies of children often differ considerably from values obtained for adults" |
| Medical Physicist 2 | 1692-1693 | 45 | As before, children should not be lumped in with adult estimates of effective dose. | More precise estimates may be unnecessary for the purpose of guiding referrals. However, the estimates of effective dose for adults tend to contain less uncertainty than similar estimates for children. |
| Medical Physicist 3 | 1724 | 46 | Throughout the report, clarify "modality dose" (and its various permutations) with "modality radiation output". | "Modality-specific radiation output quantities…" |
| Medical Physicist 2 | 1725 | 46 | CTDIvol is a dose to a phantom designed to be used to compare relative radiation output between two different CT scanners. This has absolutely nothing to do with patient dose, to organs or otherwise, especially when the size of the patient is varying dramatically as it does in the case of pediatric patients. This is the reason that Size Specific Dose Estimate (SSDE) was created by the American Association of Physicists in Medicine specifically to provide a CT dose index that accounts for affects of patient size on the patient''s dose. Ref: AAPM website, TG204 and TG220. | "quantities (e.g. PKA, SSDE) should be used . . ." |
| Medical Physicist 2 | 1727 | 46 | This is not necessarily true for all circumstances. | "effective dose may provide an appropriate . . ." |
| Medical Physicist 3 | 1781 | 47 | Doses to family members, i.e. a small child or young sibling, should be included in this section - or mentioned within Section 5.3 elsewhere | "Doses to family members and care-givers" |
| Medical Physicist 2 | 1791-1793 | 47 | This sentence is more confusing and helpful to some readers. These readers will not understand the nuances of ''reference'' person, ''approximate'' indicator, ''general'' terms, and ''appropriate'' caveats. These readers will interpret the statement to state that it is okay to assign effective doses to individual workers or patients. The statements that this is not appropriate, which occur elsewhere in the document need to be repeated here. | |
| Medical Physicist 2 | 1814 | 48 | Table 5.2 suggests a typical range of effective doses for different types of diagnostic x-ray exams. These associations may be correct for adult imaging (some still are high based on typical doses delivered 5 to 10 years ago), but they are clearly incorrect for pediatric imaging. For example, the vast majority of children (< 5 yr) imaged in my pediatric facility receive an air Kerma entrance exposure < 1 mGy for barium enemas, upper GI, VCUG, or video swallow fluoroscopic examinations. I never bother to estimate effective dose for these exams because I am more interested in potential organ doses of the directly irradiated tissues of these patients. But I do know that the effective dose associated with entrance air Kerma doses < 1 mGy will be somewhere between 0.1 - 0.2 mSv. Your table lists these effective doses to be 1 - 10 mSv. Table 2.5 will cause the user to grossly overestimate the effective dose if they are correctly managing their pediatric radiation doses during routine fluoroscopic exams. This is not helpful. | Somewhere in the text you need a statement something like: " The effective dose ranges on the left of Table 5.2 associated with specific diagnostic x-ray examinations listed in the far right column apply to adult patients. If a facility is properly managing their radiation doses to their pediatric patients, the effective dose associated with these examinations may be less than those listed for the adult patients by an order of magnitude or more." |
| Medical Physicist 2 | 1900, 1905 | 51-52 | The majority of the values of cancer incidence per 100 cases listed in Tables 5.3 and 5.4 are listed to one significant figure. For the two columns that represent the exposure to children in most cases two significant figures are provided. This is inappropriate. Based on the multiple to the uncertainties and the size of each one of these uncertainties, this data can be predicted at best to 1 significant figure. This should be corrected throughout in tables 5.3 and 5.4. | |
| Medical Physicist 3 | 1942 | 54 | "THE central radiological protection quantity" is too strong as it is application dependent. | "… is accepted internationally as a central radiological protection quantity" |
| Medical Physicist 3 | 1956 | 54 | The uncertainty of radiation effects depends on dose and on the available population data. | "… as dose decreases or as smaller population subgroups are examined" |
| Medical Physicist 3 | 1956-1962 | 54 | Provide a citation for this statement | |
| Medical Physicist 3 | 1974 | 54 | Can stochastic effects be controlled?? | "Understanding the risk of schoastic effects relies…" |
| Medical Physicist 2 | 1995-2017 | 55 | As written paragraph, paragraph number 125 is a disservice to pediatric patients. The need to provide tailored care to pediatric patients is frequently overlooked and dismissed as unnecessary during patient care discussions in adult facilities which perform the majority of pediatric imaging in the US. Please do not continue this neglect. The paragraph starts out saying everybody will be lumped together. Later it states that "Protection would not be improved by introducing separate considerations . . . for children of different ages . . .". How do you know that--based on what? Then the final sentence of the paragraph contradicts the previous message by stating, "Doses to children and the fetus are considered below." Someone who reviews your document by reading only the initial sentence or two of each paragraph totally miss the appropriate message. I do agree that worrying about differences in sex and population related differences is not necessary, but the differences between the general adult population and pediatric population are more significant than the differences you have correctly dismissed. | |
| Medical Physicist 3 | 2047 | 56 | Why is it sufficient to simply group effective dose populations by ages 1 yr, 10 yr, and adult? Again, what is the threshold in sub-population differences that motivates this recommendation? | |
| Medical Physicist 2 | 2074-2075 | 56 | "preferable '' is not a strong enough term. | ". . . reference levels, estimated effective dose values should not be substituted for measurable dose quantities." |