Protection & practice
Radiation safety
The shared responsibility of keeping patients safe during treatment and protecting the radiation therapist and staff. Covers the ALARA principle, daily safety steps, and the devices used to monitor dose and contamination.
Patient safety during treatment
Steps the therapist takes at the treatment unit
Identification & consent
Verify two patient identifiers, a photo, and informed consent at every encounter before treatment.
Site & laterality check
Confirm the correct treatment site and left/right laterality before beam-on.
Plan & dose verification
Complete an independent monitor-unit check, plan review, and machine QA before the first treatment.
Reproducible setup & immobilization
Use custom immobilization devices and reference marks to reproduce the simulation position daily.
Daily image guidance (IGRT)
Acquire kV / CBCT / MV portal images and confirm alignment is within tolerance before delivery.
Accessories & bolus verification
Check that bolus, compensators, blocks, and MLC apertures match the approved treatment plan.
Pre-treatment time-out
Pause before beam-on to confirm patient, plan, site, and accessories — every fraction.
Communication & ALARA
Explain the procedure, keep the patient informed, and minimize any unnecessary exposure.
Pregnancy screening
Verify pregnancy status for patients of childbearing potential before initiating treatment.
Reaction monitoring & escalation
Coach on skin care, watch for reactions, and escalate concerns to the care team promptly.
Therapist & staff safety
Protecting those administering the radiation
ALARA principle
Keep occupational exposure As Low As Reasonably Achievable while achieving the clinical objective.
Time, distance, shielding
The three core controls: minimize time near the source, maximize distance (inverse square), and use shielding.
Personal dosimetry
Wear your assigned whole-body and extremity dosimeters at all times when working with radiation.
Active beam warnings
Confirm beam-on lights, audible signals, and area monitors are functional before entering a treatment room.
Interlocks & emergency stop
Never override door interlocks; know the location of the emergency stop buttons and how to use them.
Shielding & barriers
Use lead aprons or thyroid shields when appropriate and rely on maze/barrier design for primary protection.
Pregnancy declaration
Staff who are or may become pregnant should declare it to apply lower occupational dose limits.
Dose limits & monitoring
Track annual occupational dose limits (NCRP / NRC 10 CFR Part 20) and investigate promptly if limits are approached.
Sealed source handling
Perform source inventory, leak/wipe tests, and area surveys after brachytherapy source use.
Emergency response
Rehearse source-recovery and emergency procedures and keep emergency contact numbers posted.
Dose limits & tolerances
Annual and cumulative exposure limits (NCRP / NRC) by group
General public
- Effective dose
- 1 mSv / yr (100 mrem) above background
- Short-term allowance
- Up to 5 mSv in a single year if the 5-yr average stays ≤ 1 mSv/yr
- Lens of the eye
- 15 mSv / yr (1.5 rem) — 10 CFR 20.1301 public limit
Radiation therapist (occupational)
- Effective dose
- 50 mSv / yr (5 rem)
- Cumulative career dose
- 10 mSv × age in years — legacy NCRP guidance, no longer a formal limit but still widely taught
- Lens of the eye
- 150 mSv / yr (15 rem) — current NRC 10 CFR Part 20 limit; NCRP 180 recommends 50 mSv / yr (a 2026 NRC proposal would adopt it); ICRP 118 recommends 20 mSv / yr averaged over 5 years
- Skin / extremities
- 500 mSv / yr (50 rem)
Pregnant staff & students
- Declared pregnant worker — fetus
- 5 mSv (0.5 rem) total over the gestation
- Monthly fetal limit
- ~0.5 mSv / month once pregnancy is declared
- Students under 18
- 1 mSv / yr (100 mrem) — public limit
- Breastfeeding staff
- Avoid radioactive contamination / uptake; express & discard milk per RSO guidance
Recommendations per NCRP Report 180 (2018) and NRC 10 CFR Part 20, in addition to natural background (~3 mSv/yr). Declared pregnant workers must notify the RSO so fetal monitoring and lower limits are applied.
International dose limits (WHO / European)
WHO and European standards for the same groups — the US limits above still apply in US practice
Occupational effective dose
20 mSv / yr (Euratom BSSD; 100 mSv averaged over 5 yrs where national law allows, never > 50 mSv in one year)
Lens of the eye
20 mSv / yr (ICRP 118, adopted by Euratom BSSD)
Skin / extremities
500 mSv / yr — same as the US limit
Declared pregnancy — fetus
1 mSv over the remainder of the pregnancy
General public
1 mSv / yr effective dose
Linac calibration
IAEA TRS-398 code of practice (the European counterpart to AAPM TG-51)
European and IAEA member states follow ICRP Publication 103 and the EU Basic Safety Standards Directive 2013/59/Euratom — both built on the same justification, optimization, and dose-limitation principles as US ALARA. Study the full comparison on the WHO & EU standards page.
Safety devices & instrumentation
Personal dosimeters, Geiger counters, and monitoring devices
Personal dosimeter (TLD badge)
Thermoluminescent dosimeter badge worn on the torso to record cumulative whole-body occupational dose.
OSL dosimeter
Optically stimulated luminescence badge (aluminum oxide) — the standard for long-term occupational monitoring.
Electronic pocket dosimeter
Real-time personal dose-rate and cumulative-dose readout worn in the pocket or badge holder.
Ring / wrist dosimeter
Measures extremity dose for hands near sources, such as in brachytherapy or radiopharmacy.
Geiger-Müller (GM) counter
Sensitive survey meter for detecting low-level radiation and contamination; used for source searches and spill surveys.
Ionization chamber survey meter
Measures exposure or air-kerma rate for room surveys and source calibration checks.
Scintillation detector
High-efficiency detector for low-level photon surveys, commonly used in nuclear medicine.
Neutron detector / rem meter
Used around high-energy (>10 MV) linacs where photonuclear neutrons are produced.
Area dose-rate monitor
Fixed ambient monitor that alarms if radiation exceeds a set threshold during operation.
Well-type ionization chamber
Used with an electrometer to calibrate and verify the strength of brachytherapy sources.
Wipe-test / contamination swab
Sampled and counted to check sealed sources for leakage and surface contamination.
Beam-on warning lights & alarm
Visual and audible indicators that the beam is active and the treatment room is interlocked.