Nuclear Accident And Potassium Iodide

Given the current situation in Japan, some of you may be interested in this topic.

The full FAQ is located at the National Regulatory Committee (NRC) website, here.

Potassium Iodide

• Blocks thyroid uptake of radioactive iodine, therefore it reduces the risk of thyroid cancers that might be caused by exposure to radioactive iodine that could be dispersed in a severe nuclear accident
• It is ingested, then taken up by thyroid gland -- if taken in a proper dosage at an appropriate time, it saturates the thyroid gland so that inhaled or ingested radioactive iodine will not be accumulated in the thyroid
• Two KI tablets will protect the thyroid gland for approx 48 hours
• Population within 10 mile emergency planning zone to the nuclear power plant are at the greatest risk of exposure to radiation, therefore KI is provided to protect them from effect of exposure after an accident
• Best protective measures for nuclear accident are evacuation and sheltering. KI tablets are used to supplement evacuation or sheltering

Image from www.ask.com

Image Wisely Campaign Launched

Image Wisely is a campaign to encourage imaging providers to

• Optimize imaging examinations to use only the radiation necessary to produce diagnostic quality images
• Convey messages to the imaging team to ensure that the facility optimizes its use of radiation when imaging patients
• Communicate optimal patient imaging strategies to referring physicians, and be available for consultation
• Routinely review imaging protocols to ensure the use of the least amount of radiation necessary to acquire a diagnostic quality image for each exam

Image Wisely is a collaborative initiative of the ACR, RSNA, ASRT and AAPM

Imagine Wisely campaign initially focuses on CT

Take the PLEDGE

More information: www.imagewisely.org

Helical CT for Urolithiasis

A coronal-reformatted CT image (without IV contrast) shows an obstructing right ureterovesical junction (UVJ) stone (arrow), causing hydroureteronephrosis. There is enlargement of the right kidney with perinephric stranding (arrowheads) as a result.

Facts:

• Urolithiasis incidence in the U.S. and Europe approximately 0.1% - 0.4% of population
• Male to female ratio = 3:1
• Peak age during third to fifth decade of life
• Recurrence rate about 75% during 20 years

Detection Rates by Various Imaging Methods

• Conventional radiography 50-70%
• Intravenous urography (IVU) 70-90%
• Ultrasound 50-60%
• Normal-dose CT: sensitivity 94-100%, specificity 97%
• Low-dose CT: sensitivity 95%, specificity 95%

Advantages of CT over IVU

• Shorter examination time
• Avoid cost and complications of IV contrast
• Greater sensitivity for stone detection
• Higher potential for detection of abnormalities unrelated to stone disease
• Study directly compared low-dose (<>
• Meta-analysis of 7 studies of low-dose CT in 1061 patients showing 95% sensitivity and specificity for stone diagnosis

References

1. Liu W, Esler SJ, Kenny BJ, et al. Low-dose nonenhanced helical CT of renal colic: assessment of ureteric stone detection and measurement of effective dose equivalent. Radiology 2000;215:51-54.

2. Niemann T, Kollmann T, Bongartz G. Diagnostic performance of low-dose CT for the detection of urolithiasis: a meta-analysis. AJR 2008;191:396-401.

Occupational Radiation Dose Limits

Facts:

• International Commission on Radiological Protection (ICRP) issues periodic recommendations on radiation protection. The Commission was founded in 1928.
• ICRP's latest publication was Publication 103 (2007)
• ICRP effective dose limit for radiation worker (occupational dose limit) = 20 mSv per year when averaged over 5 years; any year limit to 50 mSv
• The most highly exposed workers are unlikely to receive regular annual effective doses more than 5 mSv
• Radiation workers should be monitored using personal dosimeter (film badges, TLDs)
• In emergency situations, occupational exposure can exceed these dose limits if lifesaving actions are involved. Older workers with low lifetime accumulated effective doses should volunteer for emergencies.

Reference:

Huda W. Review of Radiologic Physics, 3rd edition, 2009.

Image Credit: www.thermo.com

Radiation Exposure from CT, PET/CT Will Be Tracked at the NIH

Current Issues & Debates

• Controversies exist whether low-dose (less than 150 mSv) medical radiation tests are related to development of cancer.
• Model used to extrapolate the cancer risk from low-dose medical radiation exposure is a "linear-no-threshold hypothesis", which implies that any amount of ionizing radiation (even small) has a finite probability of inducing cancer.
• This approach is widely accepted and used for radiation protection regulations and guidelines by the International Commission on Radiological Protection.
• Several recent studies and news reports have raised concerns regarding radiation exposure from medical devices (particularly CT and nuclear cardiology)
• A recent study published in the Archives of Internal Medicine estimated that radiation from CT might cause 29,000 new cancers and 14,500 deaths a year. Another study in the same journal pointed out that patients may have received much higher radiation from imaging tests than previous believed. Read synopsis in the older RiT post.

Addressing These Issues by NIH

• Radiology and Imaging Sciences at the National Institutes of Health (NIH) Clinical Center will incorporate radiation dose exposure reports into the electronic medical record (EMR)
• The process will be developed in corporation with major equipment vendors beginning with exposures from CT and PET/CT
• Radiation dose will be recorded, entered into DICOM header for CT and PET/CT and stored either in radiology information system or preferably hospital-based EMR. It should be trackable by patients in their own personal health records

What Will It Do?

• It is the first step toward monitoring patient dose
• It is the basis for future research on this subject
• Who knows, in the future this may be required in all institutions...

Are you monitoring patient dose of CT and PET/CT in your institution? If yes, how?

Reference:

Neumann RD, Bluemke DA. Tracking radiation exposure from diagnostic imaging devices at the NIH. J Am Coll Radiol 2010;7:87-89.

CT Radiation Exposure in Real Clinical Practice and Cancer Risk Estimation

Two recent studies published in the Archives of Internal Medicine in December 2009 could serve as an eye opener for every physicians ordering CT scans as well as radiologists.

Smith-Bindman et al collected CT dose data of 11 most common CT study types performed in 4 hospitals in San Francisco Bay Area. They found that there were wide variations in dose within each study type and between different types. For example, routine chest CT dose ranged from 2 to 24 mSv, routine abdomen-pelvis CT with IV contrast dose ranged from 4-45 mSv. Median effective doses for each exam were higher than they were commonly quoted in the literature, for example, 8-10 mSv is common quote for a chest CT examination. They also estimated the risk of developing cancer related to CT in several patient groups according to patient's age at the time of CT. Based on their calculation, 1 in every 80 women who undergo a chest CT for suspected pulmonary embolism at age 20 will develop cancer. Similarly, 1 in every 270 women who undergo coronary CT angiography at age 40 will develop cancer.

Berrington de Gonzalez et al utilized Medicare claim data and IMV Medical Information Division survey to project estimated age-specific cancer risk from CT studies performed in the U.S. in 2007. Excluding CT studies done for cancer diagnosis and within the last 5 years of life, 2% (29,000) excess cancers caused by CT scans in 2007 were predicted.

What is needed?

1. Optimization and standardization of CT protocols and techniques to limit radiation
2. Reduction of number of CT scans
3. Collection of dose information at patient level to educate patients and health care providers about radiation exposure

References

1. Smith-Bindman R et al. Radiation dose associated with common computed tomography examinations and the associated lifetime attributable risk of cancer. Arch Intern Med 2009; 169:2078. PubMed abstract

2. Berrington de González A et al. Projected cancer risks from computed tomographic scans performed in the United States in 2007. Arch Intern Med 2009; 169:2071. PubMed abstract

Image credit: www.topnews.us

Step Lightly for Kids

The Alliance for Radiation Safety in Pediatric Imaging has recently offered free materials on dose reduction for interventional radiology procedures, and patient education materials. These have been endorsed by the American College of Radiology (ACR).

"Treat kids with care:

Step lightly on the fluoroscopy pedal.

Stop and child-size the technique.

Consider ultrasound or, when applicable, MRI guidance."

On their website "ImageGently.org", slide presentations, checklists, outlines and patient brochures are available for free download.

Above image from www.ImageGently.org

Estimate CT Radiation Exposure

Figure 1: A screenshot of "Dose Report" showing three series of a pelvic CT scan, scan range, CT dose index (mGy), dose linear product (DLP, mGy-cm). A total exam DLP is automatically calculated (in yellow circle). From the DLP, we can calculate an effective dose by multiplying it with an E/DLP conversion coefficient. The conversion coefficients vary from one area to another.

Figure 2: A table showing E/DLP conversion coefficients of five body regions, and typical mean effective doses and dose ranges from an investigation performed in British Columbia, Canada in 2004.

In our example, the total DLP was 555.78, and it was a pelvic CT scan (conversion coefficient = 0.019).

Effective dose (mSv) = DLP x E/DLP conversion coefficient

= 555.78 x 0.019

= 10.56

Reminder: Natural effective dose of radiation received by general population = 3-4 mSv per year

Related posts:

• Radiation risk at a given effective dose range.
• Understanding what is an effective dose.

Another option to calculate an effective dose and cancer risk is to do it online, for example, a website www.XrayRisk.com

Reference:

1. Aldrich JE, Bilawich A, Mayo JR. Radiation doses to patients receiving computed tomography examinations in British Columbia. Can Assoc Radiol J 2005;57:79-85.

2. European Commission. European guidelines on quality criteria for computed tomography. EUR 16262 EN. Luxembourg: Office for Official Publication of the European Communities; 2000.

Suspected Pulmonary Embolism in Pregnant Patient (3)

Figure: Axial CT image of the chest (PE protocol) shows filling defects (arrows) in the subsegmental branches of bilateral lower lobe pulmonary arteries in a pregnant woman at her 7-week gestation.

Second-line Imaging Tests

CT Pulmonary Angiography

• Now accepted standard for imaging diagnosis of PE
• In pregnant women, number of nondiagnostic CTPA may be higher than in non-pregnant population given an increased circulatory volume and altered cardiac output
• CT venography portion should be replaced with lower extremity ultrasound to reduce radiation exposure
• Dose reduction methods include (but not limited to): decrease mA, KVP and Z-axis coverage

Lung Scintigraphy

• Consider in patients with normal chest radiograph and no history of asthma or COPD
• Consider in patients with contraindication for iodinated contrast agent ie severe allergic reaction, impaired renal function
• Dose reduction methods include (but not limited to): elimination of ventilation scan if perfusion scan negative, decrease dose of perfusion scan by half

Other Imaging Options

• MRI without gadolinium can be performed by true fast imaging with steady-state precession, but limited evaluation to first-order pulmonary arteries
• Conventional angiography is reserved only for unstable patients needing mechanical clot lysis, or when other tests are nondiagnostic

Reference:

Pahade JK, et al. Imaging pregnant patients with suspected pulmonary embolism: what the radiologist needs to know. Radiographics 2009; 10.1148/rg.293085226 (Published online before print on March 30, 2009)

Suspected Pulmonary Embolism in Pregnant Patient (2)

Potential algorithm for pulmonary embolism diagnosis in pregnant women (adapted from Pahade JK, et al. Radiographics 2009; 10.1148/rg.293085226)

First-Line Imaging Tests

Why Perform Chest Radiography?

• Search for other causes of symptoms
• Use to triage for further test, ie to perform lung scintigraphy or CT pulmonary angiography as the next test
• Normal chest radiograph does not exclude PE

Why Perform Lower Extremity Ultrasound?

• Positive result can be used to justified anticoagulation without further imaging
• Negative result should warrant further imaging in the setting of clinically suspected PE because PE may occur in the absence of DVT, isolated pelvic DVT may occur without DVT in lower extremities
• DVT is more common in the left lower extremity (more than right)

Reference:

Pahade JK, et al. Imaging pregnant patients with suspected pulmonary embolism: what the radiologist needs to know. Radiographics 2009; 10.1148/rg.293085226 (March 30, 2009)

Suspected Pulmonary Embolism in Pregnant Patient (1)

Figure: Transverse ultrasound image of the right femoral vein shows no evidence of deep vein thrombosis in a pregnant patient (7-week gestational age) presenting with acute dyspnea. Her subsequent CT pulmonary angiography shows multiple subsegmental pulmonary emboli.

Pulmonary Embolism in Pregnancy

• One in 1,000 to 10,000 pregnancies in prenatal period
• Risk of PE increases five fold during pregnancy
• Risk of PE increases with successive trimester and puerperal period (some studies demonstrated equal risks among different trimesters)
• Mortality up to 15-30%
• PE is a preventable cause of maternal death

Clinical Problems

• Difficult clinical diagnosis because of several conditions can mimic PE in pregnant patients, including normal physiologic change of pregnancy
• D-dimer assay not helpful if positive

Imaging Diagnosis

• No current standard guideline for imaging of PE in pregnant patients
• Algorithm depends on institutional preference, resource availability and individual radiologist/physician practice pattern
• Usual first-line imaging tests are chest radiography and lower extremity ultrasound

Reference:

Pahade JK, et al. Imaging pregnant patients with suspected pulmonary embolism: what the radiologist needs to know. Radiographics 2009; 10.1148/rg.293085226 (published online ahead of print on March 30, 2009)

Biological Effects of Radiation Used in Imaging (3): Risks

Excess Risks of Mortality from Solid Cancer in Human

• Dose >100 mSv
• Dose 50-100 mSv
  
• Dose 10-50 mSv (i.e. to lung or breast in retrospective-ECG-gated cardiac CT, pediatric abdominal CT)
• Unclear risk if dose <10>

Natural effective dose of radiation received by general population = 3-4 mSv per year

Radiation risks

• Negligible (<0.1>
• Extremely low (0.1 - 1 mSv) - abdomen radiograph, lumbar spine radiograph
• Very low (1-10 mSv) - head CT, chest CT, abdomen CT (adult)
• Low (10-100 mSv) - multiphase CT
• Moderate (>100 mSv) - interventional procedures, repeat CT

Reference:
Verdun FR. Radiation risk: what you should know to tell your patients. Radiographics 2008 (September).

Biological Effects of Radiation Used in Imaging (2): Stochastic Effect

Stochastic Effect of Radiation

• Effect of radiation that occurs by chance.
• Late effect such as cancer and genetic defects
• Probability (not severity) depends on dose. "As doses increase, the chance of cancer or genetic defect increases."
• No threshold dose
• Effects can occur even in human never been exposed to radiation above background level (remember normal background radiation from standing on Earth).
  

Effective Dose

• This term is used to determine probability of health effect from radiation (i.e. stochastic effects)
  
• Unit = Sv (sievert)
  
• Derived from calculation of i.e. entrance skin dose (based on dose indicator used in radiography), dose-area product (based on dose indicator in fluoroscopy), and CT dose index (based on dose indicator in CT)
• Good for dose optimization of procedures and balance radiation risks and information obtained from imaging
• Example: posteroanterior chest radiograph - <0.1>

Reference:
Verdun FR, et al. Radiation risk: what you should know to tell your patients. Radiographics 2008 (September)

Biological Effects of Radiation Used in Imaging (1): Non-stochastic Effect

What Determines Biological Effects of Radiation on Human?

1. Type of radiation
2. Amount of radiation
3. Rate
4. Part of body
5. Age of individual
6. Biological difference among individual

The effects of ionizing radiation upon humans are often broadly classified as being either stochastic or nonstochastic.

Non-stochastic Effects of Radiation

• Acute effect, typically with a very large dose in a short time
• There is a threshold dose, i.e. exposure below this dose would not cause such effects.
• Severity (magnitude) of effect is directly proportional to dose.
• Evident in hours or days
• Erythema, burns, cataract, sterility, radiation sickness and death
• Not typical for imaging procedure, which typically employs lower dose of radiation

Reference:
NDT

Imaging During Pregnancy: What Are the Risks of MRI?

Facts

• Safety aspect of MRI with respect to fetus 'has not been established'.
• Maternal concern of MRI use is similar to nonpregnant patients - can be addressed by prescan screening.

What Are the Risks to Fetus?

1. Terotogenesis: heating effect and direct nonthermal interaction of electromagnetic field may be mechanisms. Studies of children exposed to MRI in utero (1.5 Tesla) did not show negative effects at F/U up to 9 yrs of age. No study at higher magnetic field.
   
2. Acoustic damage: loud noise generated by MR, scanner coils esp with echo planar imaging. Studies have shown that fetus would probably receive a sound intensity of less than 90 dB (120 dB is a near-dangerous level). This appears to be a theoretical rather than a real concern.
   

How To Deal?
According to ACR (American College of Radiology), all pregnant women can receive MRI as long as the risk-benefit ratio to the patient warrants that the study be performed.

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การทำ MRI ในหญิงมีครรภ์นั้น มีทำกันได้ทั่วๆ ไปในสหรัฐอเมริกา มีงานวิจัยทั้งในสัตว์ทดลองและในมนุษย์ ว่า MRI ไม่มีอันตรายต่อทารกในครรภ์ แต่ทั้งนี้ งานวิจัยดังกล่าวเป็นการวิจัยที่ไม่ได้มี subject มาก, และยังติดตามผลได้ไม่นาน ทำให้ข้อมูลเกี่ยวกับความปลอดภัยของ MRI ในหญิงตั้งครรภ์ยังไม่ถือว่าเด็ดขาด ดังนั้น ถ้าต้องการทำ MRI ในหญิงตั้งครรภ์ทุกครั้งต้องอธิบายให้ผู้ป่วยทราบถึงความเสี่ยงที่อาจเกิดขึ้น (เช่น teratogenicity) และต้องขอ informed consent เสมอ

Image source: http://www.childrensmemorial.org/depts/radiology/fetalmri.aspx

Reference:
1. Chen MM, et al. Obst Gynecol 2008;112(2):333-340 (Aug 2008)
2. Kanal E, et al. ACR guidance document for safe MR practices. AJR Am J Roentgenol 2007;188:1447-1474.

Imaging During Pregnancy: What Are the Risks of CT?

Figure: Sagittal CT image of a pregnant woman who received the scan to rule out acute appendicitis. A gravid uterus (red arrows) with placenta at its fundus, and a fetus were noted. CT was negative for acute appendicitis.

FALSE STATEMENT - "Pregnancy should be terminated after an abdominal CT in early pregnancy."

What really are the risks of doing CT scan in a pregnant woman?

1. Spontaneous Abortion: within first 2 weeks of embryonic age (all or none, meaning that failed implantation vs. survival)
   
2. Teratogenesis: 2nd - 20th weeks gestation. Mental retardation, growth restriction, behavioral defect, cataracts. Threshold dose has to be reached to produce an effect. Estimate threshold dose 5-15 rad. Single standard pelvic CT (1-4.6 rad) unlikely to cause teratogenesis.
   
3. Carcinogenesis: always the risk after irradiation of fetus in utero, regardless of dose. Risks higher with exposure in first trimester than with later. Risk increases up to 2 folds at 5 rad of exposure (risk of dying from childhood cancer increases from 1 in 2,000 to 2 in 2,000).
   

Risks and benefits should always be discussed with patients.

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การทำ CT ในผู้ป่วยที่ตั้งครรภ์มีความเสี่ยงต่อเด็กในครรภ์ใน 3 รูปแบบด้วยกัน ขึ้นกับอายุครรภ์, ปริมาณของรังสีที่ได้รับ (dose) โดยที่ในช่วง 2 สัปดาห์แรกของการตั้งครรภ์ จะเสี่ยงต่อการแท้ง (ซึ่งถือเป็น all or none phenomenon คือว่าถ้า blastocyst ยังไม่ฝังตัวก็อาจแท้ง แต่ถ้าฝังไปแล้วก็อาจไม่เป็นไร), teratogenesis จะเกิดหรือไม่ขึ้นกับ dose ถ้าถึง threshold (threshold จริงๆ ไม่มีใครทราบแน่ แต่คาดว่าประมาณ 5-15 rad) ในขณะที่ pelvic CT โดยทั่วไป dose ไม่ถึง 5 rad - อันนี้ก็ตรวจสอบกับรังสีแพทย์ที่ทำงานด้วยอีกทีนะครับ เพราะแต่ละสถานที่ก็ใช้เทคนิกแตกต่างกัน ซึ่งอาจทำให้ dose แตกต่างกันด้วย), และ carcinogenesis ซึ่งเกิดได้โดยไม่ขึ้นกับ dose และโอกาสจะสูงกว่าถ้า fetus ได้รับรังสีในช่วงอายุครรภ์น้อยๆ. อย่างไรก็ตาม โอกาสของการเป็นมะเร็งในเด็กที่ทำให้เสียชีวิต โดย baseline ก็ถือว่าน้อยมากอยู่แล้ว (1 ใน 2000) ถ้าได้รับรังสีถึง 5 rad ก็จะเพิ่มความเสี่ยงขึ้น 2 เท่า เป็น 2 ใน 2000 ซึ่งก็ยังถือว่าน้อย.

ต้องแจ้งให้ผู้ป่วยทราบถึงความเสี่ยงและประโยชน์ที่จะได้รับจากการทำ CT scan ก่อนเสมอ

Reference:
1. Chen MM, et al. Obst Gynecol 2008;112(2):333-340 (Aug 2008)
2. McCollough CH, et al. Radiographics 2007;27:909-917. (Jul - Aug 2007).

5 Simple Steps to Improve Pediatric Radiological Care Concerning Radiation Safety

The following is a direct quote from ImageGently.org, a newly organized international alliance for radiation safety in Pediatric imaging.

Here are 5 simple steps to improve patient care in your everyday practice:

1. Increase awareness for the need to decrease radiation dose to children during CT scanning. Protocol development recommendations are offered in ImageGently.org
2. Be committed to make a change in your daily practice by working as a team with your technologists, physicist, referring doctors and parents to decrease the radiation dose! Sign the pledge! Click on the link on the home page to join the image gently campaign today.
3. Contact your physicist to review your adult CT protocols and then use the simple CT protocols on this website to “down-size” the protocols for kids. More is not better….adult size KV and mAs are not necessary for small bodies.
4. Single phase scans are usually adequate. Pre- and post contrast, and delayed CT scans rarely add additional information in children yet can double or triple the dose! Consider removing multi-phase scans from your daily protocols.
5. Scan only the indicated area. If a patient has a possible dermoid on ultrasound, there is rarely need to scan the entire abdomen and pelvis. “Child-size” the scan and only scan the area required to obtain the necessary information.