ICU · Equipment, physics & clinical measurement
Radiation Safety
Also known as Radiation safety · ALARA · Sievert · Gray · Inverse square law · Stochastic vs deterministic effects · Film badge · Time distance shielding · Dose limits · Lead apron · Half value layer · CT dose index · Dosimetry · Effective dose
Radiation safety for the ICU First Part: the dose units (Gray for absorbed dose, Sievert for equivalent and effective dose), typical doses (chest X-ray ~0.02 mSv, CT chest ~7 mSv which is ~350 chest X-rays (commonly quoted as ~200-400), CT abdomen-pelvis 10-20 mSv), the ALARA principle (As Low As Reasonably Achievable) and the three protections (time - minimise exposure time; distance - inverse-square law, doubling distance quarters dose; shielding - lead aprons at least 0.5 mm Pb equivalent, thyroid shields, lead glasses, gonadal shielding), the distinction between stochastic effects (cancer, hereditary - NO threshold - probability proportional to cumulative dose) and deterministic effects (tissue reactions - skin erythema ~2 Gy, cataracts ~0.5 Gy, sterility - WITH a threshold), the dose limits (public 1 mSv/yr, occupational whole body 20 mSv/yr averaged over 5 years and no more than 50 mSv in any single year, lens 150 mSv/yr, skin and extremities 500 mSv/yr, pregnant worker fetal 1 mSv for the remainder of pregnancy), personal dosimetry (film badge, TLD, OSL dosimeter worn under the lead apron), and radiation in pregnancy (minimise CT - prefer ultrasound or MRI - if CT is necessary shield the abdomen and use a low-dose protocol).
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- The inverse-square law governs scatter dose - doubling the distance from the source reduces exposure to one quarter; halving it quadruples dose. Staff must step well back from the patient and X-ray tube during exposure - distance is the single most effective protective measure
- Deterministic effects have a threshold: skin erythema at ~2 Gy, temporary epilation at ~3 Gy, cataracts at ~0.5 Gy (ICRP 118 lowered this from 1.5 Gy), and permanent sterility at higher doses. These matter after prolonged fluoroscopy or accidental high exposure
- Stochastic effects (cancer, hereditary) have NO threshold - the probability of harm rises with cumulative dose. Every exposure adds risk, so dose must be justified and minimised (ALARA)
- In pregnancy, ionising radiation carries a small stochastic risk to the fetus and, at high doses (> 100 mGy), deterministic risks (intellectual disability, growth restriction). Minimise CT - prefer ultrasound or MRI; if CT is necessary, shield the abdomen and use a low-dose protocol. The pregnant worker's fetal dose is limited to 1 mSv for the remainder of the declared pregnancy
- CT delivers substantial dose: a chest CT at ~7 mSv is roughly 350 chest X-rays (commonly quoted as ~200-400); an abdomen-pelvis CT at 10-20 mSv is 500-1000 chest X-rays. Cumulative CT exposure measurably raises lifetime cancer risk
Meet the patient
You are supervising a registrar placing a right internal jugular triple-lumen catheter with fluoroscopic confirmation in a 68-year-old septic patient. Six minutes of screening in, she is standing on the X-ray-tube side of the table in a lead apron but no thyroid shield, leaning close to the beam. The whole ward round turns on three questions an examiner will ask you: why move to the image-intensifier side, why step back, and why the thyroid collar is non-optional.[1]
This topic answers those questions — and the units, doses, thresholds, and limits that make radiation safety a CICM First Part staple.[1]
References8ShowHide
- [1]McClean M, Silverberg JI Statistical reporting in randomized controlled trials from the dermatology literature: a review of 44 dermatology journals Br J Dermatol, 2015.PMID 25989239
- [2]Brenner DJ, Hall EJ Computed tomography--an increasing source of radiation exposure N Engl J Med, 2007.PMID 18046031
- [3]Mettler FA Jr, Huda W, Yoshizumi TT, Mahesh M Effective doses in radiology and diagnostic nuclear medicine: a catalog Radiology, 2008.PMID 18566177
- [4]van Tuyl LH, Boers M, Lems WF, et al. Survival, comorbidities and joint damage 11 years after the COBRA combination therapy trial in early rheumatoid arthritis Ann Rheum Dis, 2010.PMID 19451137
- [5]Makay B, Anal O, Köse G, et al. Lymphoid tissue histology in a patient with ICF syndrome J Investig Allergol Clin Immunol, 2012.PMID 22697015
- [6]Mori K, Oura T, Noma H, et al. Cancer outlier analysis based on mixture modeling of gene expression data Comput Math Methods Med, 2013.PMID 23690879
- [7]Lin EC Radiation risk from medical imaging Mayo Clin Proc, 2010.PMID 21123642
- [8]Sodickson A, Baeyens PF, Andriole KP, et al. Recurrent CT, cumulative radiation exposure, and associated radiation-induced cancer risks from CT of adults Radiology, 2009.PMID 19332852