Medical Imaging and Radiation Dr. Bhavin Jankharia Jankharia Imaging
There is no evidence that low-level radiation from medical imaging causes harm1. Amis Stephen. Radiology 2011: 261: 52. Position Statement of the Health Physics Society3. American Association of Physicists in Medicine – position statement. Dec 20114. Hendee William R. Radiology 2012: 264: 312
Radiation in high doses, as withaccidents, nuclear bombs and with radiotherapy causes damage
The doses in such cases areupwards of 100 mSV and often much more
This damage can be non-stochastic (skin burns, exfoliation, loss of hair, diarrhea, etc), which is dose related….
…or stochastic, which are random events and include DNA mutations, etc. that can lead to cancer
Medical ImagingModalities•X-Ray•Computed Tomography•Mammography•Nuclear Medicine incl PET/CT
Radiation NumbersNormal•Normal background - 3 mSv / year (chest x-ray is 0.1 mSv and chest CT scan is 5-7 mSv).•The average per person radiation in the US because of medical imaging has now gone up to around 6 mSv / year, much less in India.
Radiation NumbersNormal•Essentially, normally any person will receive upto 50 mSv of radiation in the first 17 years andthen up to 250 mSv till age 80.
Below 50-100 mSv of exposure, the risks of health effects are either toosmall to be observed or non-existent Position Statement of the Health Physics Society
Risks of medical imaging at patient doses below 50 mSV for single procedures or 100 mSv for multipleprocedures over short time periods are too low to be detectable and may be nonexistent. Position Statement of the American Association of Physicists in Medicine, Dec 2011
Based on Japanese bomb survivordata, risks have been extrapolated
Radiation NumbersRisk•0.7 to 2.0 % of all cancers are supposed to bedue to low level radiation
These extrapolations have often led to sensationalistic reports in the media
Based on the CT scans done in 2007, the NationalCancer Institute projects 29,000 excess cancers… http://www.npr.org/templates/story/story.php?storyId=121436092
The total number of new cancers per year is around 1.6 million in the US. The lifetime risk of getting any kind of cancer is 1 in 2 to 1 in 3http://www.cancer.org/acs/groups/content/@epidemiologysurveilance/documents/document/acspc-031941.pdf
So unfortunately, this often causes moreharm than good because some patients and guardians refuse life-saving or required medical imaging procedures based on these media reports
Radiation RiskRetrospective Study•180,000 patients underwent 280,000 CT scans below 22 years of age•The estimate is that one head CT scan performed in the first decade of life would produce one excess case of brain tumor and one excess case of leukemia per 10,000 patients who underwent CT scan, in the first decade after exposure Pearce M et al. Lancet. Published online, June 7, 2012
It is known that children are particularly moresusceptible to radiation and there is no questionthat the radiation dose used should be as low as possible. The risk however is small and as long as the study is justified, not really relevant.
And while the study’s data and conclusions have not been particularly challenged, inthe end, this is a retrospective study. What is required are prospective studies that address this issue.
Two 35 years old men with suspected acuteappendicitis need CT scans. One is a radiationvirgin, the other has had 20 CT abdomen pelvis studies for treated testicular cancer in the last 10 years with a cumulative dose of 180 mSv Eisenberg et al. Radiology 2012; 263: 626
Radiation RiskSunk Cost Effect and Cumulative Dose Issues•The risk from radiation is stochastic and hence is a one-time risk related to that particular test.•Cumulative dose is irrelevant.•The risk therefore for both patients is the same. Eisenberg et al. Radiology 2012; 263: 626
But, going with the assumption that we should use radiation wisely…
...the radiology community has takensignificant steps to reduce radiation...
ALARA (Keeping Radiation Dose As Low As Reasonably Achievable)
ASARA (Keeping Medical Procedures as Safe as Reasonably Achievable)
AHARA (Keeping Medical Benefits as High as Reasonably Achievable)
Radiation ControlStakeholders•Vendors•Radiologists and other health workers•Regulatory authorities
Radiation ControlVendors•Radiation reduction technology•Protocols that use less radiation
Radiation ControlRadiologists and other health workers•Optimal use of investigations•Using non x-ray based techniques wherever feasible•Using protocols with the lowest radiation possible that still allows accurate diagnosis
Radiation ControlRegulatory Authorities•Monitoring proper use•Accrediting only appropriate personnel
ConclusionSummary•There is increasing exposure to low level radiation from medical imaging•While there is little hard evidence that this is harmful to people, there is concern based on extrapolated data from Japanese bomb explosion survivors•All stakeholders are working hard to reduce radiation exposure