Editing CT scan (section)

=== Scan dose ===
{|  class="sortable wikitable" style="float: right; margin-left:15px; text-align:center"
|-
!Examination
!Typical [[Effective dose (radiation safety)|effective <br /> dose]] ([[Sievert|mSv]])<br /> to the whole body
!Typical [[Absorbed dose|absorbed <br /> dose]] ([[Gray (unit)|mGy]])<br /> to the organ in question
|-
|Annual background radiation
|2.4<ref name="background" />
|2.4<ref name="background" />
|-
|Chest X-ray
|0.02<ref name="FDADose">{{Cite web |year=2009 |title=What are the Radiation Risks from CT? |url=https://www.fda.gov/radiation-emittingproducts/radiationemittingproductsandprocedures/medicalimaging/medicalX-rays/ucm115329.htm |url-status=live |archive-url=https://web.archive.org/web/20131105050317/https://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/MedicalImaging/MedicalX-Rays/ucm115329.htm |archive-date=2013-11-05 |website=Food and Drug Administration}}</ref>
|0.01–0.15<ref name="crfdr" />
|-
|Head CT
|1–2<ref name="Furlow2010" />
|56<ref name="nrpb2005">Shrimpton, P.C; Miller, H.C; Lewis, M.A; Dunn, M.  [http://www.hpa.org.uk/web/HPAwebFile/HPAweb_C/1194947420292 Doses from Computed Tomography (CT) examinations in the UK – 2003 Review] {{webarchive|url=https://web.archive.org/web/20110922122151/http://www.hpa.org.uk/web/HPAwebFile/HPAweb_C/1194947420292 |date=2011-09-22 }}</ref>
|-
|Screening [[mammography]]
|0.4<ref name="Risk2011">{{Cite journal |last1=Davies |first1=H. E. |last2=Wathen, C. G. |last3=Gleeson, F. V. |date=25 February 2011 |title=The risks of radiation exposure related to diagnostic imaging and how to minimise them |journal=BMJ |volume=342 |issue=feb25 1 |pages=d947 |doi=10.1136/bmj.d947 |pmid=21355025 |s2cid=206894472}}</ref>
|3<ref name="Brenner2007" /><ref name="crfdr" />
|-
|Abdominal CT
|8<ref name="FDADose" />
|14<ref name="nrpb2005" />
|-
|Chest CT
|5–7<ref name="Furlow2010" />
|13<ref name="nrpb2005" />
|-
|[[Virtual colonoscopy|CT colonography]]
|6–11<ref name="Furlow2010" />
|
|-
|Chest, abdomen and pelvis CT
|9.9<ref name="nrpb2005" />
|12<ref name="nrpb2005" />
|-
|Cardiac CT angiogram
|9–12<ref name="Furlow2010" />
|40–100<ref name="crfdr" />
|-
|[[Barium enema]]
|15<ref name="Brenner2007" />
|15<ref name="crfdr" />
|-
|Neonatal abdominal CT
|20<ref name="Brenner2007" />
|20<ref name="crfdr" />
|-
|colspan=3| {{Further|Template:Effective dose by medical imaging type}}
|}

The table reports average radiation exposures; however, there can be a wide variation in radiation doses between similar scan types, where the highest dose could be as much as 22 times higher than the lowest dose.<ref name="Furlow2010" /> A typical plain film X-ray involves radiation dose of 0.01 to 0.15&nbsp;mGy, while a typical CT can involve 10–20&nbsp;mGy for specific organs, and can go up to 80&nbsp;mGy for certain specialized CT scans.<ref name="crfdr">{{Cite journal |vauthors=Hall EJ, Brenner DJ |date=May 2008 |title=Cancer risks from diagnostic radiology |journal=The British Journal of Radiology |volume=81 |issue=965 |pages=362–78 |doi=10.1259/bjr/01948454 |pmid=18440940 |s2cid=23348032}}</ref>

For purposes of comparison, the world average dose rate from naturally occurring sources of [[background radiation]] is 2.4&nbsp;[[mSv]] per year, equal for practical purposes in this application to 2.4&nbsp;mGy per year.<ref name="background">{{Cite journal |vauthors=Cuttler JM, Pollycove M |year=2009 |title=Nuclear energy and health: and the benefits of low-dose radiation hormesis |journal=Dose-Response |volume=7 |issue=1 |pages=52–89 |doi=10.2203/dose-response.08-024.Cuttler |pmc=2664640 |pmid=19343116}}</ref> While there is some variation, most people (99%) received less than 7&nbsp;mSv per year as background radiation.<ref>{{Cite book |url=https://books.google.com/books?id=qCebxPjdSBUC&pg=PA164 |title=A half century of health physics |publisher=Lippincott Williams & Wilkins |year=2005 |isbn=978-0-7817-6934-1 |editor-last=Michael T. Ryan |location=Baltimore, Md. |page=164 |editor-last2=Poston, John W.}}</ref> Medical imaging as of 2007 accounted for half of the radiation exposure of those in the United States with CT scans making up two thirds of this amount.<ref name="Furlow2010" /> In the United Kingdom it accounts for 15% of radiation exposure.<ref name="Risk2011" /> The average radiation dose from medical sources is ≈0.6&nbsp;mSv per person globally as of 2007.<ref name="Furlow2010" /> Those in the nuclear industry in the United States are limited to doses of 50&nbsp;mSv a year and 100&nbsp;mSv every 5 years.<ref name="Furlow2010" />

[[Lead]] is the main material used by radiography personnel for [[shielding (radiography)|shielding]] against scattered X-rays.

==== Radiation dose units ====
The radiation dose reported in the [[Gray (unit)|gray or mGy]] unit is proportional to the amount of energy that the irradiated body part is expected to absorb, and the physical effect (such as DNA [[double strand breaks]]) on the cells' chemical bonds by X-ray radiation is proportional to that energy.<ref>{{Cite journal |vauthors=Polo SE, Jackson SP |date=March 2011 |title=Dynamics of DNA damage response proteins at DNA breaks: a focus on protein modifications |journal=Genes Dev. |volume=25 |issue=5 |pages=409–33 |doi=10.1101/gad.2021311 |pmc=3049283 |pmid=21363960}}</ref>

The [[sievert]] unit is used in the report of the [[effective dose (radiation)|effective dose]]. The sievert unit, in the context of CT scans, does not correspond to the actual radiation dose that the scanned body part absorbs but to another radiation dose of another scenario, the whole body absorbing the other radiation dose and the other radiation dose being of a magnitude, estimated to have the same probability to induce cancer as the CT scan.<ref>[http://www.aapm.org/pubs/reports/RPT_96.pdf The Measurement, Reporting, and Management of Radiation Dose in CT] {{webarchive|url=https://web.archive.org/web/20170623014823/https://www.aapm.org/pubs/reports/rpt_96.pdf |date=2017-06-23 }} "It is a single dose parameter that reflects the risk of a nonuniform exposure in terms of an equivalent whole-body exposure."</ref> Thus, as is shown in the table above, the actual radiation that is absorbed by a scanned body part is often much larger than the effective dose suggests. A specific measure, termed the [[computed tomography dose index]] (CTDI), is commonly used as an estimate of the radiation absorbed dose for tissue within the scan region, and is automatically computed by medical CT scanners.<ref>{{Cite journal |vauthors=Hill B, Venning AJ, Baldock C |year=2005 |title=A preliminary study of the novel application of normoxic polymer gel dosimeters for the measurement of CTDI on diagnostic X-ray CT scanners |journal=Medical Physics |volume=32 |issue=6 |pages=1589–1597 |bibcode=2005MedPh..32.1589H |doi=10.1118/1.1925181 |pmid=16013718}}</ref>

The [[equivalent dose]] is the effective dose of a case, in which the whole body would actually absorb the same radiation dose, and the sievert unit is used in its report. In the case of non-uniform radiation, or radiation given to only part of the body, which is common for CT examinations, using the local equivalent dose alone would overstate the biological risks to the entire organism.<ref>{{Cite book |last1=Issa |first1=Ziad F. |title=Clinical Arrhythmology and Electrophysiology |last2=Miller |first2=John M. |last3=Zipes |first3=Douglas P. |date=2019-01-01 |publisher=Elsevier |isbn=978-0-323-52356-1 |pages=1042–1067 |chapter=Complications of Catheter Ablation of Cardiac Arrhythmias |doi=10.1016/b978-0-323-52356-1.00032-3}}</ref><ref>{{Cite web |title=Absorbed, Equivalent, and Effective Dose – ICRPaedia |url=http://icrpaedia.org/Absorbed,_Equivalent,_and_Effective_Dose |access-date=2021-03-21 |website=icrpaedia.org}}</ref><ref>{{Cite book |last=Materials |first=National Research Council (US) Committee on Evaluation of EPA Guidelines for Exposure to Naturally Occurring Radioactive |url=https://www.ncbi.nlm.nih.gov/books/NBK230653/ |title=Radiation Quantities and Units, Definitions, Acronyms |date=1999 |publisher=National Academies Press (US)}}</ref>

==== Effects of radiation ====
{{Further|Radiobiology}}
Most adverse health effects of radiation exposure may be grouped in two general categories:
*deterministic effects (harmful tissue reactions) due in large part to the killing/malfunction of cells following high doses;<ref>{{Cite book |last1=Pua |first1=Bradley B. |url=https://books.google.com/books?id=7fpyDwAAQBAJ&q=deterministic+effects&pg=PA53 |title=Interventional Radiology: Fundamentals of Clinical Practice |last2=Covey |first2=Anne M. |last3=Madoff |first3=David C. |date=2018-12-03 |publisher=Oxford University Press |isbn=978-0-19-027624-9}}</ref>
*stochastic effects, i.e., cancer and heritable effects involving either cancer development in exposed individuals owing to mutation of somatic cells or heritable disease in their offspring owing to mutation of reproductive (germ) cells.<ref>Paragraph 55 in: {{Cite web |title=The 2007 Recommendations of the International Commission on Radiological Protection |url=http://www.icrp.org/publication.asp?id=ICRP%20Publication%20103 |url-status=live |archive-url=https://web.archive.org/web/20121116084754/http://www.icrp.org/publication.asp?id=ICRP+Publication+103 |archive-date=2012-11-16 |website=[[International Commission on Radiological Protection]]}} Ann. ICRP 37 (2-4)</ref>

The added lifetime risk of developing cancer by a single abdominal CT of 8 mSv is estimated to be 0.05%, or 1 one in 2,000.<ref>{{Cite web |date=March 2013 |title=Do CT scans cause cancer? |url=https://www.health.harvard.edu/staying-healthy/do-ct-scans-cause-cancer |url-status=dead |archive-url=https://web.archive.org/web/20171209152338/https://www.health.harvard.edu/staying-healthy/do-ct-scans-cause-cancer |archive-date=2017-12-09 |access-date=2017-12-09 |website=[[Harvard Medical School]]}}</ref>

Because of increased susceptibility of fetuses to radiation exposure, the radiation dosage of a CT scan is an important consideration in the choice of [[medical imaging in pregnancy]].<ref>{{Cite web |last=CDC |date=2020-06-05 |title=Radiation and pregnancy: A fact sheet for clinicians |url=https://www.cdc.gov/nceh/radiation/emergencies/prenatalphysician.htm |access-date=2021-03-21 |website=Centers for Disease Control and Prevention |language=en-US}}</ref><ref>{{Citation |last1=Yoon |first1=Ilsup |title=Radiation Exposure In Pregnancy |date=2021 |url=http://www.ncbi.nlm.nih.gov/books/NBK551690/ |work=StatPearls |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=31869154 |access-date=2021-03-21 |last2=Slesinger |first2=Todd L.}}</ref>

==== Excess doses ====
In October, 2009, the US [[Food and Drug Administration]] (FDA) initiated an investigation of brain perfusion CT (PCT) scans, based on [[radiation burn]]s caused by incorrect settings at one particular facility for this particular type of CT scan. Over 200 patients were exposed to radiation at approximately eight times the expected dose for an 18-month period; over 40% of them lost patches of hair. This event prompted a call for increased CT quality assurance programs. It was noted that "while unnecessary radiation exposure should be avoided, a medically needed CT scan obtained with appropriate acquisition parameter has benefits that outweigh the radiation risks."<ref name="Furlow2010">{{Cite book |last=Whaites |first=Eric |url=https://books.google.com/books?id=qdOSDdETuxcC&q=Typical+effective+dose&pg=PA27 |title=Radiography and Radiology for Dental Care Professionals E-Book |date=2008-10-10 |publisher=Elsevier Health Sciences |isbn=978-0-7020-4799-2 |pages=25}}</ref><ref>{{Cite journal |vauthors=Wintermark M, Lev MH |date=January 2010 |title=FDA investigates the safety of brain perfusion CT |journal=AJNR Am J Neuroradiol |volume=31 |issue=1 |pages=2–3 |doi=10.3174/ajnr.A1967 |pmc=7964089 |pmid=19892810 |doi-access=free}}</ref> Similar problems have been reported at other centers.<ref name="Furlow2010" /> These incidents are believed to be due to [[human error]].<ref name="Furlow2010" />