In this episode we take a deep dive into the rise of CT scanning in America. Do we get too many CT scans? How much does this harm us? What level of variation in CT scanning exists from doc to doc? Then we spiral back to overdiagnosis. Finally, we talk DNR vs “allowing natural death.”
CT scanning [preamble]
- Also known as “CAT scanning” (Computerized Axial Tomography)
- Franke: “tomos” = slice / section, “graphia” = describing
- Invented in the 1970s by an engineer and a physicist
- First, CT was used for only head imaging but whole body imaging came later
- What CT looked like in 1975 (1 image = DAYS) vs. Today (4 images = 350 ms)
CT scanning — are we scanning too much?
“Computed Tomography — An Increasing Source of Radiation Exposure.” NEJM. 2007. https://www.nejm.org/doi/full/10.1056/nejmra072149
- ½ – body, ⅓ – head, 75% in hospital setting 25% in clinic
- Fields with rising CT use: Peds diagnosis and adult screening
- Absorbed dose: Energy absorbed per unit of mass (Units = grays) — measures organ dose. Better for risk estimation.
- Effective dose: dose distributions that are not homogenous (which is usually the case). Based off of a generic estimate of the overall harm.
General conclusion: With all things considered, CT scans have given us a lot benefits to medicine. A lot of progress has been made in decreasing the amount of radiation while increasing the quality and number of images we can get. We’re able to spend less time the CT machine and we’re able to control for artifacts like breathing and peristalsis much better, but it doesn’t mean it’s a perfect tests without any risk. CT still has much higher doses of radiation than plain-film. Based on that, there’s still a case that too many CTs are being performed by the United States. This may be based on over-scanning for certain diagnoses. The article mentioned chronic headaches, blunt trauma, and seizures. Weaknesses (is that too harsh?) in our healthcare system were also discussed, like when someone changes healthcare systems and they have to get rescanned and re-exposed. [Summary and bullets above by: Kim]
“Variation in use of all types of computed tomography by emergency physicians.” Am J Emerg Med. 2013. https://www.ncbi.nlm.nih.gov/pubmed/23998807
- Looked at 195,801 eligible visits → 44,724 of which resulted in at least 1 CT scan.
- The adjusted rate of CT ordering by providers was 23.8% of patient visits
- ranging from 11.5% to 32.7%
- The upper quartile of providers was responsible for 78% of the CT scans ordered above the mean.
- There was an 8-fold variation in use of CT abdomen in discharged patients.
- High head CT use by providers predicts high use in all other CT types.
CT scanning — studies of cumulative exposure
I mentioned that being a mile away from an atomic bombing works out to ~100mSv of exposure. The citation for that is: “Effect of recent changes in atomic bomb survivor dosimetry on cancer mortality risk estimates.” Radiation Research. 2004. https://www.ncbi.nlm.nih.gov/pubmed/15447045
“Cumulative CT exposures in emergency department patients evaluated for suspected renal colic.” J Emerg Med. 2007. https://www.ncbi.nlm.nih.gov/pubmed/17692768
- Highlights of patients undergoing 9 or more CT scans during the 9-month study period:
- 28-year-old woman with 14 CT scans
- 42-year-old woman with 22 CT scans
- 53-year-old man with 25 CT scans
- The most serious diagnosis by CT in the “≥9 CT scan” patients was complicated urolithiasis.
- During the 9-month study period, 23 patients presented multiple times, in some cases undergoing multiple CT scans, including one patient who presented 10 times, underwent three normal CT scans, and was noted to have 25 CT scans in the hospital system.
I made a comment about needing only a single scan for most patients who get stones, after which most won’t need follow-up scans. Here’s some substantiation for this → Rosen’s Emergency Medicine Concepts and Clinical Practice (2017) says the following on page 1218:
“Most patients with a history of nephrolithiasis and clinical picture consistent with renal colic should not undergo any form of imaging. Imaging is appropriate in patients with a history of nephrolithiasis who do not improve with treatment, have a uri- nalysis showing infection, have a solitary or transplanted kidney, or in whom a diagnosis other than renal colic is suspected.”
“Cumulative Radiation Exposure and Cancer Risk Estimates in Emergency Department Patients Undergoing Repeat or Multiple CT.” Am J Roentgenology. 2009. → [PDF]
- We identified all patients at a tertiary care adult academic medical center with at least three emergency department visits within a 1-year period that included CT of the neck, chest, abdomen, or pelvis. For this cohort, we identified all diagnostic CT studies over the previous 7.7 years. We calculated cumulative radiation doses by summing typical effective doses of the anatomic regions scanned, and we calculated lifetime attributable risk using the population-averaged dose-to-risk conversion factor of one cancer per 1,000 patients receiving a 10-mSv dose, in accordance with the seventh Biologic Effects of Ionizing Radiation (BEIR VII) report.
- 130 emergency department patients met the inclusion criteria.
- Median of 10 CT scans, mean of 13, maximum of 70 CT scans. Seventy. Seventy f#@&ing CT scans.
- Cumulative median dosage 91mSv, mean of 122, and maximum of 579 mSv
- Emergency department studies comprised 55% of those captured.
- Repeat imaging of the same study type represented at least half of the imaging for 72% of the cohort and all of the imaging for 12%.
CT scanning — cancer risks
“Projected cancer risks from computed tomographic scans performed in the United States in 2007.” Arch Int Med. 2009. https://www.ncbi.nlm.nih.gov/pubmed/20008689
- In a previous study, we used risk projection models and detailed survey data on CT scan use in the United Kingdom (UK) in the early 1990s and estimated that approximately 0.2% of incident cancers in the UK could be attributable to CT scans. Based on our estimates, a recent review suggested that, because current use in the US is 10 times higher than it was in the UK in the early 1990s, this figure might now be as high as 1.5% to 2% in the US.
- To date, attention has focused on risks from pediatric CT scans. However, our estimates suggest that in terms of absolute numbers the potential public health impact of current use patterns is highest for adults aged 35 to 54 years, particularly women, because of the high frequency of use.
“Radiation dose associated with common computed tomography examinations and the associated lifetime attributable risk of cancer.” Arch Int Med. 2009. https://www.ncbi.nlm.nih.gov/pubmed/20008690
EBM: Overdiagnosis (…in cancer)
[Overdiagnosis = diagnosing something that is a “true positive” by some lab/histo/etc standard, but isn’t clinically meaningful]
AN ETHICAL TAKE: “A definition and ethical evaluation of overdiagnosis. Journal of Medical Ethics. 2016. (doi:10.1136/medethics-2016-103822) https://jme.bmj.com/content/42/11/705
BREAST CANCER: “Likelihood that a woman with screen-detected breast cancer has had her “life saved” by that screening.” Arch Intern Med. 2011. https://www.ncbi.nlm.nih.gov/pubmed/22025097
Some potentially useful numbers from a different paper by same author → for every woman who avoids a death from breast cancer due to mammography screening…
- Between 2 and 10 women will be overdiagnosed and treated needlessly
- Between 5 and 15 women will be told that they have breast cancer earlier than they would otherwise, yet have no effect on their prognosis
- Between 200 and 500 women will have at least one “false alarm” (50–200 will be biopsied)
THYROID CANCER: “Overdiagnosis of Thyroid Cancer: Answers to Five Key Questions” Acad Radiol. 2015.
- The incidence of papillary thyroid cancer in US has doubled in the last decade, whereas before 2002, the incidence of papillary thyroid cancer doubled over a 30-year period.
- South Korea → 15-fold increase in thyroid cancer incidence in an 8-year period with no change in mortality
- Thyroid cancer ranks as the ninth most common cancer in the United States and the fifth most common cancer in women.
- In 1993, Black and Welch proposed explanation for overdiagnosis related to advancing diagnostic tech
- The best evidence for how commonly patients die with rather than from thyroid cancer is from autopsy studies.
- Harach et al examined 2.5-mm-thin sections → 36% of adults harbored occult papillary thyroid cancers ranging in size from 0.15 to 14 mm
- In order to avoid unnecessary operations it is suggested that incidentally found small OKs (less than 5 mm in diameter) were called occult papillary tumor instead of carcinoma.
The field is literally changing the definition of papillary cancer to respond to decades of overdiagnosis and overtreatment. For more on this:
- “Nomenclature Revision for Encapsulated Follicular Variant of Papillary Thyroid Carcinoma; A Paradigm Shift to Reduce Overtreatment of Indolent Tumors.” JAMA Oncology. 2016. [Pubmed]
- A 2017 paper (https://academic.oup.com/jnci/article/109/7/djx153/3958324 ) in the NCI’s own journal states that, “Jochen Lorch, MD, MS, director of the thyroid center at the Dana–Farber Cancer Institute in Boston also noted that doctors are developing ways to reduce overtreatment that can result from overdiagnosis. He pointed to the new diagnostic criteria published in the August 2016 JAMA Oncology (see one bullet up) that reclassified one type of thyroid cancer as a noninvasive growth that did not need to be treated. The change could allow about 10,000 people per year in the U.S. to avoid thyroid cancer treatment.“
“DNR” (Do Not Resuscitate) vs “AND” (Allow Natural Death)
In keeping with the ‘spiraling’ theme of this episode, we close our our discussions by spiraling back to framing effects while looking at different ways of talking about death (and why we sometimes avoid it, or get it wrong).
“Allow Natural Death’ versus Do Not Resuscitate: three words that can change a life.” J Med Ethics. 2008. https://www.ncbi.nlm.nih.gov/pubmed/18156510
“Allow Natural Death versus Do Not Resuscitate: What Do Patients with Advanced Cancer Choose?” J Palliat Med. 2015. https://www.ncbi.nlm.nih.gov/pubmed/25825919
- The first 100 consenting adult patients with advanced cancer were surveyed regarding their diagnosis, prognosis, and attitudes about critical care and resuscitation. They were then presented with hypothetical scenarios in which a decision on their code status had to be made if they had one year, six months, or one month left to live. Half were given a choice between being “full code” and “DNR,” and half could choose between “full code” and “AND.”
- All 93 of the participants who completed the survey were considered by their attending physician to have a terminal illness, but only 42% of these interviewees believed they were terminally ill. In addition, only 25% of participants thought that their primary oncologist knew their EOL wishes.
[This PBS clip is absolutely worth your time to watch; it gets at the essence of the difficulties many have in coming to terms with what the future may hold]
— Episode credits —
Hosted by Addie, Kim, and Alex. Audio production and editing by Addie. Show notes written by Addie. Theme music (Too Cool, and Laserpack) by Kevin MacLeod of incompetech.com, licensed under Creative Commons: By Attribution 3.0 License.