RADIATION PROTECTION

Question 1

formula for HVL

Answer 1

HVL = 0.693/u

I = Io e ^-ux

Question 2

what is primary radiation and what type of barrier is used for it

Answer 2

primary radiation is the radiation that has emerged from the x-ray tube that has yet to be attenuated, thus requiring a primary barrier

primary protective barrier is located perpendicular to the undeflected line of travel of the xray beam

Question 3

what is secondary radiation and what type of barrier is used for it

Answer 3

secondary radiation includes scattered and leakage radiation, and requires a secondary barrier

secondary protective barriers are walls that are not in the direct line of travel of the primary beam

Question 4

what is workload (W) and its formula

Answer 4

in diagnostic radiograohy facilities: defined as milliampere minutes of beam-on time per week

calculated by multiplying no of patients per week by mAs per patient

W = (mAs/pt) x (pts/wk)

in radiation therapy facilities: defined as the weekly dose delivered at 1m from the source (cGy/week at 1m)

calculated by multiplying no of patients per week by dose per patient

Question 5

what is use factor (U)

Answer 5

defined as the fraction of operating time during which radiation is directed towards a particular barrier

U applies to primary beam

Question 6

what is occupancy factor (T)

Answer 6

defined as the fraction of time that the space (that is to be shielded) is occupied

occupancy factor for controlled areas must always be 1

zero occupancy - underground

Question 7

how does distance affect the radiation intensity

Answer 7

reduction of radiation intensity by increasing distance - always more effective than additional shielding due to inverse square law

Question 8

what are the 3 fundamental principles by ICRP

Answer 8

justification - any exposure to patient must result in more good than harm

optimization - all exposures are to be kept as low as reasonably achieveable, social and economic factors taken into account

dose limit - exposure individuals should not exceed the limits recommended for the appropriate circumstances -> does not apply to medical radiation exposures

Question 9

what is the dose limit for occupationally exposed workers >18 years

Answer 9

stochastic effect (whole body) - effective dose of 20mSv/year averaged over 5 years (ie 100mSv in 5 years), not exceeding more than 50mSv in any year

deterministic effect (eye lens) - equivalent dose of 150mSv/year
deterministic effect (skin) - equivalent dose of 500mSv/year

Question 10

what is the equivalent dose limit to the surface of a pregnant woman’s abdomen

Answer 10

2mSv from declared, for the remainder of the pregnancy

Question 11

what is the dose limit for members of the public

Answer 11

stochastic (whole body) - effective dose of 1mSv/year

deterministic (eye lens) - equivalent dose of 15mSv/year
deterministic (skin) - equivalent dose of 50mSv/year

annual dose limit may be exceeded under special circumstances, provided that the avg dose over 5years does not exceed 1mSv per year

Question 12

what are the 4 quartets of radiation protection

Answer 12

personal action - shielding, time, distance

activities of the department - control access, shield, monitor/survey, training

administrative structure - recommendations, laws, regulation, licensing, accreditation

philosophy - justification, optimization, limitation

Question 13

what is the annual dose from b/g radiation in singapore

Answer 13

0. 8mSv from inhalation and terrestrial radiation from the ground
1. 4mSv from ingestion of food and water

<0.1mSv from cosmic rays

Question 14

what are the responsibilities of a medical radiation professional

Answer 14

• responsibility to the patient
• responsibility to oneself as a radiation worker
• duty to continuing education
• responsibility in dose optimization in the effective application of the ALARA principle

Question 15

what are the radiation protection organisations

Answer 15

1. ICRP
2. ICRU
3. IAEA
4. UNSCEAR
5. BEIR committee

• NEA is the national authority for radiation protection in Singapore
• the RPNSD of NEA administers and enforces radiation protection act and ionizing radiation regulations, through a system of licensing, notification, authorization, inspection and enforcement

Question 16

how to determine the licensing for x-ray measurement for a particular shielding for people outside of the radiation room?

Answer 16

licensing for x-ray measurements is performed at the maximum continuous tube current, ie 3-5mAs at 150kVp

nowhere outside the x-ray room accessible to any individual should have a radiation level exceeding 10uSv per hour while the X-ray machine is being operated at its max rated current, max rated voltage, at its normal operation position

Question 17

where is the weakest and strongest scatter radiation for a C-arm flurorscopy

Answer 17

weakest - on the side of the patient, away from the x-ray tube

strongest - on the side of the patient, closer to the x-ray tube

Question 18

define controlled and uncontrolled area and give examples

Answer 18

controlled area - limited access area in which the occupational exposure of personnel to radiation-producing equipment is supervised by an individual with L5 or L6 license

example: treatment room/ xray room/ console room

example of an uncontrolled room: lobbies/ offices/ waiting area/ examination or consultation room/ restrooms

Question 19

explain the shielding calculations rationale

Answer 19

shielding calculations are conservative - calculated shielding values tend to be larger than needed for radiation protection - to plan for a safer environment or worst-case-scenario.

• field size and phantom size employed for scatter calculations are up to 4x higher than those typically used
• high occupancy periods are used, for eg, within an uncontrolled area
• materials in the x-ray room that reduce radiation transmission not included in calculations

Question 20

name some of the safety devices in radiation treatment rooms

Answer 20

• door interlocks to turn off radiation beam when circuit is interrupted
• safety edges cause door to retract when activated so door will not close on the object when accidentally touched
• warning lights to indicate when beam is ‘on’ - inside and outside the treatment rooms
• operator must be able to see and hear the patient during the treatment
• emergency power off switches

Question 21

reporting of radiation incidents

Answer 21

L5 or L6 licensee has to notify the appropriate authorities (eg MOH) and RPNSD to

• give a preliminary oral report within 24h
• which is to be confirmed in writing within 48h and
• submit a full written report of the accident within 10 days