1. THE BASIS FOR RADIATION PROTECTION
Radiation Protection (Radiation Safety) - Includes private and public promotion of those practices that limit exposure to ionizing radiation to the smallest amount.
ALARA- As Low As Reasonably Achievable

2. Cardinal Principles of Radiation Protection
Time – minimize
Distance – maximize. Utilizes the Inverse Square Law. The intensity varies inversely with the square of the distance because of the divergence of the beam
Shielding – maximize. Amount a protective barrier can reduce radiation intensity can be estimated by HVL or TVL

3. PROPERTIES OF X-RAYS Penetrating electromagnetic waves
Heterogenous energy
Travel in straight line
Travel at the speed of light
Cannot be focused by lens nor do they reflect off surfaces
No charge
No mass
Produce secondary & scatter radiation
Cause certain crystals to fluoresce (give off light)
Affect photographic film
Cause ionization in matter
Cause biologic changes

4. When X-rays come out of the X-ray tube they can:
Pass through the body unaffected
Be absorbed by the body through Photoelectric interaction
Interact with tissue and change direction through Compton interaction - creates scatter radiation.

5. Terms:
Primary radiation - X-rays exiting the x-ray tube through the tube window
Leakage radiation - X-rays exiting the tube other than through the tube window
Remnant radiation (exit radiation/image forming radiation) -primary beam that passes through the patient without interacting with tissue.
Scatter radiation - radiation that interacted with tissue and has gone in a different direction than primary radiation
Secondary radiation - radiation that is generated by patient tissue interactions

6. Units Utilized in Rad. Protection
Exposure: radiation intensity/ charge measured in air. Unit: Roentgen (R) or coulomb per kg
Radiation Dose: measures radiation energy absorbed as a result of exposure. Unit: Rad or Gray. 1Gy = 100rads
Radioactivity – quantity of radioactive material. Unit: Curie or Becquerel

7. Dose Equivalent Limits
Dose limits have been established and implemented by the NCRP report #116
Occupational exposure is described as Dose Equivalent
Dose Limits are specified for exposure to:
Whole Body
Partial Body
Organ
Exposure of General Population

8. Occupational exposures(annual)
Effective dose equivalent limit (stochastic effect) 50 mSv/ 5rem
Dose equivalent limits for tissues and organs (nonstochastic)
Lens of eye mSv / 15rem
All others (e.g., red bone marrow, breast, lung…) 500 mSv / 50rem
Guidance: cumulative exposure
10 mSv x age / 1rem x age

9. Public exposures(annual)
Effective dose equivalent limit, continuous or frequent
1 mSv / 0.1rem
2. Effective dose equivalent limit, infrequent exposure
5 mSv / 0.5 rem
3. Dose equivalent limits for lens of eye, skin and extremities
50 mSv / 5rem
Education and training exposures (annual)
Effective dose equivalent limit 1 mSv / 0.1 rem
Dose equivalent limits for lens of eye, skin and extremities
Embryo-fetus exposures
Total dose equivalent limit 5 mSv / 0.5 rem
Dose equivalent in a month 0.5 mSv / 0.05 rem

10. Design of X-ray Equipment
There are protection requirements for x-ray equipment to decrease patient and personnel exposure
Orthovoltage and Superficial voltage- Leakage radiation must be reduced to less than 1cGy/hour at a distance of one meter from the housing
Co60 - Leakage radiation at 1 meter from head of unit cannot exceed 2mrem/hr. Maximum leakage is 10mrem/hr at any distance.
LINAC - Leakage less than 0.1% of highest primary beam rate at 1meter for largest field size

11. Protective Barrier Design
Controlled Area – defined area in which the occupational exposure of personnel to radiation is under the supervision of the radiation protection supervisor
Dose Limit is 100mRem/wk
Uncontrolled area – Can be occupied by anyone. Dose limits must be reduced to less than 2mRem/week

12. Radiation Signs & Regulatory Agencies
These agencies perform radiation research and determine limits for radiation exposure and its possible effects. They do not make or enforce laws
ICRP – International Council on Radiation Protection
NCRP – National Council on Radiation Protection
NRC - Nuclear Regulatory Commission
This commission reviews recommendations made by the other agencies and enforces them as law
Federal and state agencies require that locations where radioactive material and radiation producing machinery are used or stored be posted with one or more warning signs
Sign used depends on the type and amount of radioactivity or radiation level

13. “RADIOACTIVE MATERIAL”-Sign is required when the quantity of radionuclide exceeds the activity specified in the appropriate federal or state regulation.
“CAUTION – RADIATION AREA”-Sign is necessary when an employee could receive in any 1 hour a dose in excess of 5mrem or greater than 100mrem in 5 consecutive days.
“CAUTION HIGH RADIATION AREA” or “ CAUTION AIRBORNE RADIOACTIVITY AREA-Signs necessary when dose rate exceeds 100mrem per hour and for areas in which the concentrations of radioactivity in air exceed certain standards specified in the regulations.

14. Duties of the QA Team Radiation Oncologist responsible for:
Appropriateness of treatment
Care of patient
Chart rounds
Medical Physicist responsible for:
Baseline testing of equipment
Calibration of equipment
Weekly chart checks
Treatment Planning
Radiation Safety

15. Duties of the QA Team Radiation Therapist responsible for:
Accurate, reproducible daily radiation treatment
Check of patient’s chart
Performs warm-up daily and checks certain interlocks and safety switches daily or weekly as required
Keeps treatment room in good condition and stocked

16. General Room Conditions
Treatment rooms, simulator rooms, and exam rooms must be/have
Clean and orderly
Lights, heat and room temperature controls operating correctly
Routine supplies available
Emergency supplies available
Frequency: DAILY

17. Checking ODI
Materials needed: include mechanical distance indicator as well as a ruler to check accuracy of mechanical distance indicator.
Performance Steps:
Attach the mechanical distance indicator to the treatment head.
Set the ODI distance at isocenter directly to the table top
Attach the magnetic scale to the indicator
ACCEPTABLE TOLERANCE: +/- 2mm
Frequency: Monthly

18. Functions of Light Field
Guide portal size
Guide to radiation beam position
Guide to portal shape

19. Tolerance
Light/radiation field congruence is +/-3mm however stricter guidelines recommend +\-2mm
If not within tolerance MUST call a physicist and DO NOT TREAT

20. Flatness and Symmetry
Purpose: Determine that the useful 90% of beam is flat and symmetrical
Measuring for homogeneous radiation across the beam.
Malfunction will cause underdose/overdose to tumor and normal surrounding tissue.
Flatness – A dose variation of +/-3% is considered acceptable
Symmetry – The dose should not differ by more that 2% at any pair of points situated symmetrically with respect to CAX
Frequency – yearly, but most sites do monthly test.