Discover the most frequently asked questions that were sent to Radiological Protection Committee of the CPR-CBR.
Access the complete collection:
Does radiation from medical devices increase the incidence of cancer in the population?
Currently, there is no conclusive scientific evidence of a link between an increased likelihood of developing cancer and the application of ionizing radiation in low-dose diagnostic procedures. However, some studies, based on limited statistics, suggest that the radiation levels applied in computed tomography procedures may slightly increase the risk of developing radiation-induced cancer in the future, particularly in pediatric patients.
There is a consensus that the benefit of obtaining an accurate diagnosis, which allows for defining the most appropriate clinical approach to patient treatment, far outweighs the potential risks of this radiological technique.
To maximize the benefits of radiation applications in diagnosis, procedures must be well-justified and optimized. In a radiological examination, the lowest possible dose should be administered to the patient while maintaining the image quality required for diagnosis.
Source:
Risks from CT scans – what do recent studies tell us? J. Radiol. Prot. 34 (2014) E1–E5
UNSCEAR 2013: Effects of Radiation Exposure of Children
NCRP Report 171 (2012): Uncertainties in the Estimation of Radiation Risks
Radiol Clin North Am. 2009 January ; 47(1): 27–40. doi:10.1016/j.rcl.2008.10.006. Mayo Clin Proc. • December 2010;85(12):1142-1146 www.mayoclinicproceedings.com
Cynthia H. McCollough1. The Role of the Medical Physicist in Managing Radiation Dose and Communicating Risk in CT. AJR 2016; 206:1241–1244.
Are magnetic resonance imaging (MRI) and ultrasound free of ionizing radiation?
None of the techniques They use X-rays to obtain images. There is no scientific data indicating that magnetic resonance imaging (MRI) and ultrasound are associated with any risk of cancer.
How many computed tomography (CT) scans can a person undergo?
There is no established maximum limit to the number of computed tomography (CT) scans an individual can undergo, provided there is a well-founded clinical indication and appropriately optimized protocols. Previous examinations and alternative imaging techniques should be considered before performing another CT scan. Special attention should be paid to pediatric patients, who exhibit greater radiosensitivity than adults.
Source:
IAEA WHO.Bonn call for action: 10 actions to improve radiation protection in medicine in the next decade. 2012. p. 16. Published online. Accessible at: https://www.who.int/publications/m/item/bonn-call-for-action
How does the radiation dose from computed tomography (CT) compare to other methods, such as X-rays and scintigraphy?
In general, radiation doses from CT scans to the patient are higher than in other radiological diagnostic procedures. Currently, the radiation dose associated with a routine CT scan ranges from 1 to 14 mSv depending on the examination, comparable to the annual dose received from natural radiation sources such as radon and cosmic radiation (1-10 mSv), depending on where the person lives. Thus, the risk to an individual exposed to radiation in a CT scan would be comparable to annual levels of environmental radiation.
The effective dose of a CT scan can vary between 50 and 400 times the dose of a chest X-ray, depending on the technical parameters used.
In the case of nuclear medicine, in scintigraphy procedures, the values vary between 1.2 mSv and 23 mSv, depending on the study. These effective dose values are comparable to those observed in computed tomography procedures. Tables 1 and 2 present the effective dose values for different examinations in nuclear medicine and CT, respectively.
Table 1: Average effective doses in nuclear medicine examinations
Procedure | Effective dose (mSv) |
Bone scintigraphy with MDP-Technetium-99m | 3,6 |
Myocardial scintigraphy MIBI-Technetium-99m | 4,2 |
DMSA-Technetium-99m renal scintigraphy | 2,5 |
Pulmonary perfusion MAA-Technetium-99m | 1,2 |
Myocardial scintigraphy with thallium-201 chloride | 23 |
Parathyroid thallium chloride | 18 |
Thyroid scintigraphy with sodium iodide (I-123) | 3,4 |
CT scans | Average effective dose (mSv) | Equivalent number of PA chest radiographs (0.02 mSv each) |
Head | 2 | 100 |
Neck | 3 | 150 |
Calcium count | 3 | 150 |
Pulmonary angiography | 5,2 | 260 |
Column | 6 | 300 |
Chest | 8 | 400 |
Coronary angiography | 8.7 | 435 |
abdomen | 10 | 500 |
Pelvis | 10 | 500 |
Virtual colonoscopy | 10 | 500 |
Chest (pulmonary embolism) | 15 | 750 |
Source:
(https://rpop.iaea.org/RPOP/RPoP/Content/InformationFor/Patientspatient-information-computed-tomography/index.htm) radiol Clin North Am, 2009; 47 (1): 27-40.
Effective doses in Radiology and diagnostic nuclear medicine: A catalogue, Radiology 248 1 (2008) 254-263.
Radiation exposure in multi-slice versus single-slice spiral CT: Results of a nationwide survey, Eur. Radiol. 13 (2003)1979-1991.
Revised radiation doses for typical x-ray examinations, Br. J Radiol. 70 833 (1997) 437-439.
Radiation dose and cancer risk estimates in 16-slice computed tomography coronary angiography. J. Nucl. Cardiol. 15 2 (2008) 232-240.
How can I be sure that the clinic where I am having my CT scans done is taking the necessary radiation protection measures?
To ensure that the CT scan service complies with radiation protection requirements, it is recommended to verify that:
1) Does the facility have an operating license from the health authorities?
To obtain the permit, the service must meet the radiological protection requirements established in current ANVISA legislation.
2) Does the facility have the Quality Seal in Computed Tomography from the Brazilian College of Radiology and Diagnostic Imaging?
To obtain the quality seal, the facility undergoes an evaluation by the tomography committee, composed of a group of radiologists and a physicist. The following requirements are observed in this evaluation process:
- a) Qualifications of service professionals;
- b) Image quality assessment: the committee's group of radiologists analyzes CT scan images from different procedures provided by the service and their respective reports;
- c) Radiation protection criteria, which include radiation doses, are observed by the commission's physicist.
Furthermore, the CBR has an accreditation program (PADI) for diagnostic imaging clinics, which includes auditing of tomography services.
3) Does the service have a radiation protection program?
It is recommended that the patient or their guardian check with the service to determine what radiation protection measures are in place for the patient, such as: whether there are specific protocols for pediatrics and what measures the service has adopted to optimize examinations.
Is it safe to perform CT scans on children?
When performed properly, the benefits of a computed tomography (CT) scan far outweigh the risks. CT scans can provide detailed information for diagnosis, treatment planning, and assessment of a patient's clinical condition. Furthermore, they can eliminate the need for exploratory surgery.
The risk of cancer in children due to radiation exposure is approximately two to three times higher than in adults because pediatric patients have a longer life expectancy and their organs are more sensitive to radiation. For newborns, the risk of inducing cancer is essentially the same as in the second and third trimesters of pregnancy. Therefore, it is crucial that the examination be optimized to obtain an accurate diagnosis.
Pediatric protocols, with specifically established exposure parameters, should be used, as well as current modulation systems and low kV techniques. As an international consensus, the examination needs to be performed in only one phase, avoiding the pre-contrast phase whenever possible.
Source: www.imagegently.org
UNSCEAR 2013: Effects of Radiation Exposure of Children
Is it possible to know the radiation dose from a CT scan? Can anyone access this information?
Yes, all CT scanners provide two dose descriptors: Volume Computed Tomography Dose Index (CTDIvol) or volumetric CTDI and Dose Length Product (DLP) or dose-length product. However, these values should only be used as an estimate of the dose during the procedure. As they are obtained from phantoms (16 and 32 cm), these values do not represent the characteristics of each patient and, therefore, cannot be considered as the doses received by the patient, especially in Pediatrics.
To obtain a more accurate estimate according to a patient's specific anatomical region, a methodology was developed that includes correction factors, considering the patient's dimensions. The method for this analysis can be found in the following publication:
Size Specific Dose Estimation (SSDE) in Pediatric and Adult body CT Examination– American Association of Physicists in Medicine report of task group 204 (2011)
Source:
Size Specific Dose Estimation (SSDE) in Pediatric and Adult body CT Examination– American Association of Physicists in Medicine report of task group 204 (2011).
Is there a radiation risk associated with accompanying a patient in the CT scan room?
The risk of accompanying a patient during a CT scan is very low. However, any exposure to radiation should be avoided. The presence of a companion in the room during the procedure should only be allowed when strictly necessary for the examination. When the presence of a companion is indispensable, all radiation protection measures must be adopted to minimize their exposure to radiation. It is recommended that the companion, parents or family members, wear a lead apron and thyroid protector during the procedure. The technician should be informed if there is a possibility that the companion is pregnant to avoid her exposure.
Source:
Resolution RDC No. 330, of December 21, 2019 – ANVISA
Are there ways to reduce or control the radiation dose from a CT scan?
Yes, it is possible to reduce radiation doses without compromising image quality for diagnosis. Initially, it must be ensured that the examination has been properly justified and that alternative techniques such as ultrasound and magnetic resonance imaging have been considered. The best balance between image quality and radiation dose should be ensured by adopting the following optimization strategies:
– Adjust the protocols for patient groups considering age range, biotype, sex, and clinical indication;
– Reduce the number of scan phases, using only the necessary ones (examinations with intravenous contrast);
– Avoid repeating unnecessary tests;
– Use automatic dose control whenever possible;
– Reduce the mAs as much as possible, considering the acceptable noise level for diagnosis;
– Limit the scan length, restricting it to the region of interest;– Use immobilization devices whenever possible;
– Avoid using pitch low;
– Use interactive reconstruction methods;
It is recommended to compare the institution's CTDIvol and DLP values for a defined sample of patients with established international reference levels.
- When available, use a dose modulator (mA) during CT scan acquisition.
Diagnostic Reference Levels (DRLs) and Achievable Doses (ADs) for Adult and Pediatric CT in CTDIvol
Procedure Lateral dimension of | patient | Phantom diameter (cm) | CTDIvolNRD (mGy) | CTDIvolAD(mGy) |
Head – (adult) | 16 | 16 | 75 | 57 |
Abdomen-pelvis (adult) | 38 | 32 | 25 | 17 |
Chest (adult) | 35 | 32 | 21 | 14 |
Head (pediatric – 5 years) | 15 | 16 | 40 | 31 |
Abdomen (pediatric – 5 years) | 20 | 16 | 20 | 14 |
Source:
ACR–AAPM Practice Parameter for Diagnostic Reference Levels and Achievable Doses In Medical X-Ray Imaging (August 21, 2015)
Are there ways to reduce or control the radiation dose from a CT scan?
Yes, it is possible to reduce radiation doses without compromising image quality for diagnosis. Initially, it must be ensured that the examination has been properly justified and that alternative techniques such as ultrasound and magnetic resonance imaging have been considered. The best balance between image quality and radiation dose should be ensured by adopting the following optimization strategies:
– Adjust the protocols for patient groups considering age range, biotype, sex, and clinical indication;
– Reduce the number of scan phases, using only the necessary ones (examinations with intravenous contrast);
– Avoid repeating unnecessary tests;
– Use automatic dose control whenever possible;
– Reduce the mAs as much as possible, considering the acceptable noise level for diagnosis;
– Limit the scan length, restricting it to the region of interest;– Use immobilization devices whenever possible;
– Avoid using pitch low;
– Use interactive reconstruction methods;
It is recommended to compare the institution's CTDIvol and DLP values for a defined sample of patients with established international reference levels.
- When available, use a dose modulator (mA) during CT scan acquisition.
Diagnostic Reference Levels (DRLs) and Achievable Doses (ADs) for Adult and Pediatric CT in CTDIvol
Procedure Lateral dimension of | patient | Phantom diameter (cm) | CTDIvolNRD (mGy) | CTDIvolAD(mGy) |
Head – (adult) | 16 | 16 | 75 | 57 |
Abdomen-pelvis (adult) | 38 | 32 | 25 | 17 |
Chest (adult) | 35 | 32 | 21 | 14 |
Head (pediatric – 5 years) | 15 | 16 | 40 | 31 |
Abdomen (pediatric – 5 years) | 20 | 16 | 20 | 14 |
Source:
ACR–AAPM Practice Parameter for Diagnostic Reference Levels and Achievable Doses In Medical X-Ray Imaging (August 21, 2015)
Can pregnant patients undergo CT scans?
CT scans in pregnant patients are not prohibited, but a precise clinical indication is necessary for their performance. Alternative diagnostic techniques that do not use ionizing radiation should be considered. However, if the CT scan is properly justified, every effort must be made to optimize the procedure, minimizing fetal exposure.
There is particular concern when performing radiation screening on a pregnant woman due to the risk of fetal exposure to ionizing radiation, particularly during the first trimester of pregnancy. The potential effects of radiation on the fetus include: embryonic, neonatal, or fetal death; congenital malformations; and functional alterations such as mental retardation, reduced intelligence quotient, and childhood cancer. The risk is related to the dose rate and total radiation dose received by the fetus and the stage of development at the time of exposure.
Examinations that require direct exposure of the fetus to the primary beam, such as abdominal examinations, deserve the greatest attention and care. For examinations in regions distant from the fetal area, the scattered radiation received by the fetus will be very small, provided the procedure is conducted properly.
Before the examination, the radiologist should discuss the indication with the referring physician, evaluating the risks and benefits of the procedure. A physicist or qualified professional should estimate the dose absorbed by the fetus. Technical parameters need to be optimized and technical factors recorded. Unnecessary exposure of the abdomen and pelvis should be avoided by limiting the exposed region as much as possible, using precise collimation and a single phase. The fetal dose needs to be reduced to the minimum necessary to obtain the diagnosis. All contrast media must be used with caution. Repeat examinations should be avoided.
It is important to emphasize that in properly optimized procedures, the doses received by the fetus are much lower than 100 mGy, which corresponds to the threshold established in international recommendations. Therefore, these procedures should not be associated with an increase in fetal anomalies or death.
Source:
Radiation Exposure and Pregnancy: When Should We Be Concerned? RadioGraphics 2007; 27:909–918
Imaging in Pregnant Patients: Examination Appropriateness. RadioGraphics 2010; 30:1215–1233 •
Report No. 174 – Preconception and Prenatal Radiation Exposure: Health Effects and Protective Guidance (2013)
A New Pregnancy Policy for a New Era. Pregnancy and Medical Radiation. ICRP Publication 84. Ann. ICRP 30 (1), 2000
How great are the mortality risks of CT scans compared to the risks of everyday life?
At low radiation doses, such as in radiological procedures, the exact magnitude of the risk is a controversial topic. This is because for doses below 100 mSv the risks are too low to be measured directly.
Assuming there is a small increase in cancer risk with low doses of radiation, it is recommended to keep dose levels as low as possible while maintaining adequate image quality for diagnosis.
The risk associated with a single or even multiple CT scans is minimal. Daily, all individuals are exposed to background radiation levels, which can vary between 3 and 10 mSv/year, depending on the region. No increase in cancer cases has been observed in regions where background radiation is higher. In CT scans, depending on the type of procedure, the radiation doses received by the patient can vary between 2 and 10 mSv. In special procedures, these values can increase to 20 to 30 mSv, but the radiation levels are still considered low. Thus, the risk to an individual exposed to radiation in a CT scan can be comparable to background radiation levels. A head CT scan and a chest CT scan correspond, on average, to 8 and 36 months of background radiation exposure, respectively. On a transatlantic flight, for example, radiation exposure would correspond to 11 days of background radiation exposure.
The risk of mortality from a CT scan is significantly lower than the risk associated with many everyday activities. For example, it has been estimated that in the US, the risk of dying while walking down the street is 32 times greater than the risk from a CT scan, and the risk of death while driving a car is 240 times greater than from a CT scan. The following table compares other types of everyday risks with radiation from CT procedures.
Source:
Translated by Fletcher JG, Kofler JM, Coburn JA, Bruining DH, McCollough CH. Perspective on radiation risk in CT imaging. 2012 Jul 27;38(1):22–31.
Figure 1: Visual representation of the probability of death from various causes, compared to dying from a radiation-induced malignancy from abdominal or cranial CT scans, using risk assumptions as outlined in BEIR VII and a linear hypothesis without a threshold. Source: Fletcher (2012).