Examenes radiologicos y riesgo de cancer en pacientes

EXAMENES RADIOLOGICOS Y

RIESGO CARCINOGENICO EN

PACIENTES: SDSDFSD

RESUMEN DE ALGUNOS ESTUDIOS Y

PERSPECTIVAS ACTUALES

Jesús Aponte Ortiz

Médico Residente de primer año – Radiología

Hospital Víctor Lazarte

Julio 2012

Effective Doses of X – ray exams

Effective Doses of X – ray exams

Radiation exposures of X – ray exams

• RadioGraphics 2001; 21:1033–1045

Radiation exposures of X – ray exams

• RadioGraphics 2001; 21:1033–1045

American Association of Physicists in

Medicine. • http://www.aapm.org/org/policies/details.asp?id=318&type

=PP

• AAPM POSITION STATEMENT ON RADIATION RISKS

FROM MEDICAL IMAGING PROCEDURES

Policy text • The American Association of Physicists in Medicine (AAPM) acknowledges that

medical imaging procedures should be appropriate and conducted at the lowest radiation dose consistent with acquisition of the desired information.

• Discussion of risks related to radiation dose from medical imaging procedures should be accompanied by acknowledgement of the benefits of the procedures. Risks of medical imaging at effective doses below 50 mSv for single procedures or 100 mSv for multiple procedures over short time periods are too low to be detectable and may be nonexistent.

• Predictions of hypothetical cancer incidence and deaths in patient populations exposed to such low doses are highly speculative and should be discouraged. These predictions are harmful because they lead to sensationalistic articles in the public media that cause some patients and parents to refuse medical imaging procedures, placing them at substantial risk by not receiving the clinical benefits of the prescribed procedures.

• AAPM members continually strive to improve medical imaging by lowering radiation levels and maximizing benefits of imaging procedures involving ionizing radiation.

AAPM POSITION STATEMENT ON RADIATION

RISKS FROM MEDICAL IMAGING PROCEDURES

Radiation exposure and cancer… what is

already known? • First, in most cases it is difficult to predict who will be harmed,

because many negative effects of exposure to ionizing radiation,

such as cancer, are stochastic in nature (i.e., randomly occurring).

However, although the severity of such effects does not vary by

magnitude of exposure, the probability does increase with dose.

• Second, the appearance or diagnosis of radiation-induced cancers

can occur many years after exposure. Thus, it is difficult to attribute

the cancer to a specific exposure.

• Finally, much of what we know regarding cancer risk from

ionizing radiation comes from large observational studies

involving workers in the nuclear industry and atomic bomb

survivors. Exposure in these groups is by and large much

higher than those typically seen in clinical populations.

Risks to individuals exposed to radiation at doses used in

most medical imaging procedures must be extrapolated

from epidemiologic data for “high-dose” populations (e.g.,

atomic bomb survivors) using a linear “no threshold”

• However, there are no epidemiologic data to support the

validity of this model for low dose exposures (< 10

millisieverts [mSv]) and thus no direct data regarding the

risk to individuals undergoing typical medical imaging

procedures. It is likely for these reasons that health care

providers have difficulty quantifying the risks associated

with many imaging procedures, because they have little or

no epidemiologic data suitable to their patients or direct

clinical experience with known radiation-induced injuries.

• Are pre- or postnatal diagnostic X-rays a risk factor for childhood cancer? A systematic review

• Heterogeneous results were found for postnatal exposures and leukemia in four studies. No significant effect of pre- and postnatal X-ray exposure was observed for other cancer sites (non-Hodgkin lymphomas, solid tumors and brain tumors). Most studies have limitations in study design, study size, or exposure measurement.

• Computed tomography is not covered in the studies and needs to be investigated in the future.

Objective To examine childhood cancer risks associated

with exposure to diagnostic radiation and ultrasound scans

in utero and in early infancy (age 0-100 days).

Design Case-control study.

Setting England and Wales.

Participants 2690 childhood cancer cases and 4858 age,

sex, and region matched controls from the United

Kingdom Childhood Cancer Study (UKCCS), born 1976-

96.

• Exposure to diagnostic radiography in early infancy (0-

100 days) was associated with a small increase in risk of

all childhood cancer and leukaemia and a statistically

significant increase in lymphoma.

• Exposure to diagnostic radiography in early infancy was

associated with small, non-significant excess risks for all

cancers and leukaemia, as well as increased risk of

lymphoma (odds ratio 5.14, 1.27 to 20.78) on the basis of

small numbers.

Cancer risk related to low-dose ionizing radiation

from cardiac imaging in patients after acute

myocardial infarction. • Using an administrative database, we selected a cohort of

patients who had an acute myocardial infarction between

April 1996 and March 2006 and no history of cancer.

• We documented all cardiac imaging and Cancer risk

related to low-dose ionizing radiation from cardiac

imaging in patients after acute myocardial infarction.

• therapeutic procedures involving low-dose ionizing

radiation. The primary outcome was risk of cancer.

Statistical analyses were performed using a time-

dependent Cox model adjusted for age, sex and exposure

to lowdose ionizing radiation from noncardiac imaging to

account for work-up of cancer.

• Of the 82 861 patients included in the cohort, 77%

underwent at least one cardiac imaging or therapeutic

procedure involving low-dose ionizing radiation in the first

year after acute myocardial infarction. The cumulative

exposure to radiation from cardiac procedures was 5.3

milli Sieverts (mSv) per patient-year, of which 84%

occurred during the first year after acute myocardial

infarction. A total of 12 020 incident cancers were

diagnosed during the follow-up period.

Cancer risk related to low-dose ionizing radiation

from cardiac imaging in patients after acute

myocardial infarction.

• There was a dose-dependent relation between exposure

to radiation from cardiac procedures and subsequent risk

of cancer. For every 10 mSv of low-dose ionizing

radiation, there was a 3% increase in the risk of age- and

sex-adjusted cancer over a mean follow-up period of five

years (hazard ratio 1.003 per milliSievert, 95% confidence

interval 1.002–1.004).

• Interpretation: Exposure to low-dose ionizing radiation

from cardiac imaging and therapeutic procedures after

acute myocardial infarction is associated with an

increased risk of cancer.

Cancer risk related to low-dose ionizing radiation

from cardiac imaging in patients after acute

myocardial infarction.

• Radiation exposure from CT scans in childhood and

subsequent risk of leukaemia and brain tumours: a

retrospective cohort study.

Lancet 2012 4;380(9840):499-505.

• Assess the excess risk of leukaemia and brain tumours

after CT scans in a cohort of children and young adults.

• Methods In our retrospective cohort study, we included

patients without previous cancer diagnoses who were first

examined with CT in National Health Service (NHS)

centres in England, Wales, or Scotland (Great Britain)

between 1985 and 2002, when they were younger than

22 years of age. We obtained data for cancer incidence,

mortality, and loss to follow-up from the NHS Central

Registry from Jan 1, 1985, to Dec 31, 2008.

Lancet 2012 4;380(9840):499-505.

• We estimated absorbed brain and red bone marrow doses

per CT scan in mGy and assessed excess incidence of

leukaemia and brain tumours cancer with Poisson relative

risk models. To avoid inclusion of CT scans related to

cancer diagnosis, follow-up for leukaemia began 2 years

after the fi rst CT and for brain tumours 5 years after the

first CT.

Lancet 2012 4;380(9840):499-505.

Findings During follow-up, 74 of 178 604 patients were

diagnosed with leukaemia and 135 of 176 587 patients were

diagnosed with brain tumours. We noted a positive association

between radiation dose from CT scans and leukaemia

(excess relative risk [ERR] per mGy 0·036, 95% CI 0·005–0·120;

p=0·0097) and brain tumours (0·023, 0·010–0·049;

p<0·0001). Compared with patients who received a dose of less

than 5 mGy, the relative risk of leukaemia for patients

who received a cumulative dose of at least 30 mGy (mean dose

51·13 mGy) was 3·18 (95% CI 1·46–6·94) and the

relative risk of brain cancer for patients who received a

cumulative dose of 50–74 mGy (mean dose 60·42 mGy) was

2·82 (1·33–6·03). Lancet 2012 4;380(9840):499-505.

• Interpretation Use of CT scans in children to deliver

cumulative doses of about 50 mGy might almost triple the

risk of leukaemia and doses of about 60 mGy might triple

the risk of brain cancer. Because these cancers are

relatively rare, the cumulative absolute risks are small: in

the 10 years after the fi rst scan for patients younger than

10 years, one excess case of leukaemia and one excess

case of brain tumour per 10 000 head CT scans is

estimated to occur. Nevertheless, although clinical benefi

ts should outweigh the small absolute risks, radiation

doses from CT scans ought to be kept as low as possible

and alternative procedures, which do not involve ionising

radiation, should be considered if appropriate. Lancet 2012 4;380(9840):499-505.

Lancet 2012 4;380(9840):499-505.

Lancet 2012 4;380(9840):499-505.

• Cancer incidence risks to patients due to

hysterosalpingography.

• Of all the cancers considered, the incidence of cancer of

the bladder for patients undergoing HSG procedures is

more probable.

J Med Phys 2012;37:112-6

• The study was carried out at five rural hospitals (Hospital

B-F) performing HSG procedure without screening and an

urban hospital (Hospital A) with screening using II-TV for

the HSG procedure. For the study, 120 patients selected

at random were used, with 100 patients undergoing HSG

procedure without screening and the remaining 20

patients undergoing HSG procedure with screening using

II-TV. All the procedures were performed by a radiologist

with the assistance of radiographers using a film size of

24 cm x 30 cm for all cases. The radiographic images

generated were passed by a radiologist.

J Med Phys 2012;37:112-6

• Empirical risk models developed by the Biological

Effects of Ionizing Radiation (BEIR) Committee

Report VII phase two were used to estimate

excess relative cancer risk to patients due to

radiation exposure. The empirical risk models

used in this study are based on the Japanese

Atomic bomb survivors.

J Med Phys 2012;37:112-6