Radiation Protection (2023)

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  • Fundamental Principles
  • Personnel Monitoring
  • Facilities and Area Monitoring
  • Fundamental Principles

FundamentalPrinciples of radiation are significant to maintain the radiationprotection. The fundamental principles are,

  1. Justification
  2. Optimization
  3. Dose & Dose limits

These principles should be followed by each and every person who isdirectly or indirectly in the way of radiation protection. Theprinciples are explained below.

Justification:

Nouse of ionizing radiation is justified if there is no benefit.All applications must be justified. Thisimplies all, even the smallest exposures are potentially harmful andthe risk must be offset by a benefit. Justification needto evaluate the benefits of radiation and doing in easy wayespecially in the case of radiotherapy. Assessmentof the risks requires the knowledge of the dose received by persons.

Optimization:

Optimizationof the procedure is crucial phenomenon.When radiation is tobe used then the exposure should be optimized to minimize anypossibility of detriment. Optimization is“doing the best you can under the prevailing conditions”.Need to be familiar with techniques and options tooptimize the application of ionizing radiation - this is really themain objective of the present course.

Principleof Optimization:

ASLow As Reasonably Achievable (ALARA) is the main principle ofoptimization. Whatever be the procedure the optimization should bethere to minimize the risk of the effects of radiation. Optimizationcan be divided into two types one is optimizing the tumor and normalstructures and another one is optimizing the protection ofOccupational workers, patients, and Public’s.

Boththe justification and optimization are include in a part ofstrategies when handling the potential situations or procedure.

Dose& Dose limits:

Dose limits are one of the three principles ofprotection as introduced by ICRP and BSS. Fixed dose limits arerecommended by ICRP and often enforced by a national regulatory body.Dose constraints are used in an optimizationprocess to guide Treatment planning. Constraints and the importancethereof may be subject to change to achieve the optimum solution to aproblem.

“No dose limitation for medical exposure of thepatient - it is always assumed that the benefits for the patientoutweigh the risks”

“Limits need to be applied for public andoccupational exposures."

Questions:

  1. What is the principle of optimization?
  1. Distance
  2. Time
  3. Shielding
  4. ALARA

2. Dose limits are applied only for,


  1. Patients
  2. Public and Occupational
  3. Non radiation workers
  4. All

Answer:

  1. ALARA
  2. Public and Occupational

References:

  1. www.ehs.ucsc.edu
  2. International Basic Safety Standards for protectionagainst Ionizing Radiation and for the Safety of Radiation Sources.Safety Series:115
  3. ICRU History, policies and Procedures
  4. IAEA Training material on Radiation Protection inRadiotherapy.

ALARA

ALARA is an acronym for As Low AsReasonably Achievable. This term is based onthe belief that exposure to certain agents could cause potentialeffects. The concept also implies that there is a relationshipbetween the amount of exposure and the possibility of an effect.There is a risk involved in receiving the exposure. The basis for theALARA philosophy is quite simple; if you reduce your exposure tocertain agents, you reduce the potential risk of an unwanted effect.This basic method to achieve the ALARA principle is Time, Distance,and Shielding. The ALARA philosophy is based on the assumption thatexposure to radiation poses a risk. The cautiousassumption that a proportional relationshipexists between dose and effect for all doses(non-threshold concept) is the basis forALARA. There may be some risk associated with any dose. This is alsocalled the linear model of exposure.

Instructionsto Radiation workers to achieve ALARA:

Facilitieshaving the equipment producing the radiation or radioactive sourcesfor research or treatment purpose should follow the guidelines toreduce the exposure level to the individual or group who are workingin the area.

Pointsto achieve ALARA:

  • When a radiation worker working radiation facilityfirst should wear his Personnel Monitoring device.
  • Radiation worker should follow the procedures ordirections for particular to minimize exposure to him and also forthe patient.
  • Peoples other than authorised person to work or handlethe radiation source or equipment are strictly banned. It leadspotential situations.
  • Avoid the unnecessary repetition of diagnosticprocedure for particular patient. To avoid this type situationtrained persons are allowed to work.
  • Especially in nuclear medicine air borne activity andthe situation is prone to radiation. Because of that must follow theprocedures as it’s given for that work.
  • To minimize the exposure pre-planned works should beimplemented in all the works associated with radiation.
  • Non-radiation workers also should obey for postings andsigns of radiation.
  • The training programs shall be conducted byRadiological Safety Officer (RSO) to implement these types of worksor procedures.

Questions:

  1. The basic methods to reduce the exposure and to achievethe ALARA is,
  1. Time
  2. Distance
  3. Shielding
  4. All

Answer:

  1. All

References:

  1. www.ncrponline.org
  2. Radiation Safety Fundamentals Workbook by university ofCalifornia Santa crug and Environmental Health & Safety.

Basic Methods ofProtection

Basic methods of Radiation Protection consist of threestrategies Time, Distance, and Shielding. These three methods havebeen widely used till now to reduce exposure of exposure toindividuals, and public. The basic are explained briefly below.

Time:

Timeis one of the prime factors to reduce the exposure. Whatever be theradiation more time spends in that area more would be the exposureand vice versa. So, that tries to avoid the spending of more time inthe radiation areas.

Pointsto do minimize exposure:

  1. The time consuming in some potential situations can bereduce by executing the pre-planned situations and works.
  2. In Emergency situations the work can be shared by groupof people who are eligible to do that work. In this way alsoexposure will be reduce.

Radiation Protection (2)

Figure shows the three factors of radiation protection.

Distance:

Distanceis the second one need to consider when handling or working in theradiation areas. All electromagnetic radiation obeys the InverseSquare Law, means if the distance increases the intensity of theradiation decrease by square of the distance. Expression for inversesquare law is,

I1d12= I2d22

Belowfigure explains clearly the effect of distance in radiationprotection. At 1ft exposure rate 1000mR/hr but, in 2ft it reduces tonearly 1/4th ofthe earlier one. So that distance should be maintained when handlingor working with the radiation sources.

Radiation Protection (3)

Shielding:

Perhapsto time and distance, shielding is significant one in achieving theradiation protection. Though, time and distance could be factor it isnot possible to give enough distance and it is also not practicalphenomenon. So, that adequate shielding is required to protectagainst radiation.

The thickness of the shielding material could vary fordifferent materials. Most common materials used for shielding purposeare listed below.

NameDensity (gm/cm2)

  1. Lead11.35
  2. Steel7.87
  3. Concrete 2.35
  4. High Density Concrete3.8 -4.6
  5. Polyethylene0.92

Thebelow figure shows the attenuation by shielding:

Radiation Protection (4)

Questions:

  1. Exposure rate measured at 8inches is 30mR/hr. what isthe exposure at 2 inches?
  1. 400 mR/hr
  2. 480 mR/hr
  3. 450 mR/hr
  4. 470 mR/hr

2. What is the density of Lead?

  1. 11.35 gm/cm
  2. 11.35 gm/cm2
  3. 11.00 gm/cm2
  4. None of these.

Answers:

  1. 480 mR/hr
  2. 11.35 gm/cm2

References:

  1. safety series no. 115
  2. http://emilms.fema.gov
  3. www.pubiaea.com
  4. www.nrc.org
  5. Basic Radiological Physics by Dr. K. Thayalan
  • Personnel Monitoring

Personnel Monitoring

The aim of personnel monitoring is,

  1. monitor and control individual doses regularly in order to ensurecompliance with the stipulated dose limits
  2. report and investigate over exposures and recommend necessaryremedial measures urgently
  3. Maintain life time cumulative dose records of the users of theservice.

Hence,the radiation received by all the radiation workers during their workshould be regularly monitored and a complete up to date record ofthese doses should be maintained. Personnel monitoring is usuallydone by employing Film badges, Thermo luminescent dosimeters (TLD) oroptically stimulated luminance dosimeter (OSL), and pocket dosimeter.

Filmbadge:

Afilm badge is used to measure external individual doses from, x,beta, gamma and thermal neutron radiations. It consists of a filmpack loaded in a film holder having suitable metallic filters. Thefilm holder is made up of plastic with stainless steel lining asshown in the figure. It is capable of holding one or morephotographic films of size 4cm x 3cm, wrapped inside by a light tightpolythene or paper cover. The metallic filters are fixed in bothsides of the holder which help to identify the type and energy ofincident radiation. There are three types of holder chest, wrist,and head holders.

Radiation Protection (5)

Theminimum dose that the film badge can detect is 0.2mSV. The advantageof film badge is permanent record, easily can find the type ofradiation, energy and least expensive than other devices.

ThermoLuminescent Dosimeter (TLD):

Filmbadges has been replaced by TLD’s because of fading at hightemperature and humidity, high sensitivity to light, pressure andchemicals, complex dark room procedure.

TLDbadges are used currently worldwide instead of film badges. It isbased on the phenomenon of thermo luminescence, the emission of lightwhen certain materials are heated after radiation exposure. It isused to measure individual doses from x, beta, and gamma radiations.It gives very reliable results since no fading is observed underextreme climatic conditions. The typical TLD badge consist ofplastic cassette in which a nickel coated aluminium card is placed asshown in the below figure. This badge can cover a wide range of dosesfrom10mR to 10,000mR with an accuracy of ±10%.

Radiation Protection (6)

Opticallystimulated luminance dosimeter (OSL):

Dosimetersusing stimulated luminance is also available now a days alternativeto TLD. The principle of OSL is similar to TLD except the heating.Instead of heating, laser is used to stimulate light emission.Crystalline aluminium oxide activated with carbon (Al2O3:c) iscommonly used as OSL dosimeter. It has broad base response andcapable of detecting low doses as 10 mSv. The OSL dosimeter can bereuse several times and it can also differentiate between static anddynamic exposures.

PocketDosimeters:

Filmand TLD will not show accumulated exposure immediately. In additionto the regular film badges, the radiation doses received by theradiation worker can be assessed by wearing a pocket dosimeter, whichgives instantaneous radiation exposure. This is very useful innon-routine work, in which the radiation levels vary considerably andmay be quite hazardous. The main advantage of pocket dosimeter liesin its ability to provide instant on the spot check of radiation dosereceived by the personnel. Suitable protective measures can beundertaken immediately to minimize future exposures. The dose can beread off directly by the person during or after any radiation work.

Questions:

  1. What is the range of measurement of doses in TLD?
  1. 10mR to 10,000 mR
  2. 100 mR to 10,000 mR
  3. 100000 mR
  4. All

2. What is the advantage of film badge?

  1. Least expensive
  2. Permanent record
  3. Can find the energy, type of the radiation
  4. All

Answer:

  1. 10mR to 10,000 mR
  2. All

References:

  1. http://hps.org
  2. www.aerb.gov.in
  3. Text book of Radiological Physics, by Prof.K. Thayalan.
  4. The essential physics of medical imaging, second edition by J.T.Bushberg, J.Anthony Siebert, and Edwin leidholdt, JR

Embryo/FoetusExposure

Embryo or foetus exposure is the significant one when a pregnantradiation worker works in the radiation department or pregnant womenundergoing diagnostic procedure or Radiotherapy treatment.Justification and optimization and dose limits are the threeprinciples of radiotherapy. The above mentioned three principlesshould be following strictly.

Effectsof Radiation Exposure in Utero:

  1. Prenatal doses from most properly done diagnostic procedures presentno measurable increase in the risk of prenatal death, malformation,or the impairment of mental development over the backgroundincidence of these entities. Higher doses, such as those involvedin therapeutic procedures, can, however, result in significantfoetal harm.
  2. There are radiation related risks throughout pregnancy that arerelated to the stage of pregnancy and the foetal absorbed dose.Radiation risks are most significant during organogenesis and theearly foetal period, somewhat less in the second trimester, andleast in the third trimester.
  3. During the period of ±25 weeks post conception, the central nervoussystem is particularly sensitive to radiation. Fetal doses inexcess of 100mGy may result in a verifiable decrease of IQ. Duringthe same time, foetal doses in the range of 1000 mGy result in ahigh probability of severe mental retardation. The sensitivity ishighest 8±15 weeks post conception. The CNS is less sensitive tothese effects at 16±25 weeks of gestational age and ratherresistant after that.
  4. Radiation has been shown to cause leukemia and many types of cancerin both adults and children. Throughout most of pregnancy, theembryo\foetus is assumed to be at the same risk for potentialcarcinogenic effects of radiation as are children.

Doselimits for pregnant Radiation Worker:

  1. The pregnant radiation worker has the dose limits of 2mSv
  2. According to ICRP – 84 foetal doses between 100 – 500 mGy, thedecision should be based upon the individual circumstances.
  3. If the foetal dose exceeds 500mGy the significant foetal damage willoccur.

Questions:

  1. What is the dose limit for foetus or embryo?
  1. 111mGy
  2. 100mGy
  3. 95mGy
  4. None

Answer:

  1. 100 mGy

References:

  1. ICRP report 84
  2. The text book of radiological physics by Prof. K. Thayalan
  • Facilities and Area Monitoring

Required postings(signs)

Therequired postings are mandatory in the places where radiation basedjobs are being carried out. The different signs and posters are therefor different type of radiation. The signs and posters should not beplaced unsuitable places which leads to potential harm to unknownpeople or patients if enter in that area.

The required postings in the department of radiotherapy, radiologyand nuclear medicine should be placed by the Radiological SafetyOfficer (RSO). Wherever it is needed directions also should mentionto prevent the unauthorised access to the radiation source. Theseposters will guide and alert the people what to do in that area. Therequired postings for different types of energy and others mentionedbelow,

The radiation source using places for treatment, diagnostic andresearch purpose should be paste the below mentioned placard in theentrance of the door for safety of other people. The places areradiotherapy, nuclearmedicine etc.

Radiation Protection (7)

The required posting for x-ray source usage area is mentioned below.Usually x-rays are used for the diagnostic, radiotherapy treatment,and other areas of interest.

Radiation Protection (8)

Radiation Protection (9)

Eachand every hospital and diagnostic centres should use the appropriatesymbols and posters to guide the patient and other non-radiationworkers in that hospital. The Radiological Safety Officer in thehospital or diagnostic centre or research institutes should implementawareness regarding the radiation safety to the non-radiation workersin the particular institution. In that should discuss do’s anddon’ts when they are approaching the radiation area. This will helpto others indirectly in the radiation protection point of view.

The required packaging Symbols should be use during the transport ofradiation source from one place to another place. The requiredsymbols are shown below for better understanding. At any point timemisuse of this symbol is an offense under the act of the government.The transport symbol for radiation source or generating equipment ismentioned below.

Radiation Protection (10)

References:

  1. http://www.iaea.org
  2. http://www.xraytechnicianfacts.com
  3. http://www.safetysign.com

Area Monitoring Devices

The valuation of radiation levels at different locations in thevicinity of radiation installation is known as area monitoring orradiation survey. These valuations give the details about theintegrity of the radiation facility or installation. Instrumentsused for the above purposes are called radiation survey meters andarea monitors. In general, any survey meter or area monitor shouldconsist of two main parts namely. One is a device which detects theradiation and another one is a display system to measure theradiation. Following types of survey meters are generally used forradiation survey and area monitoring.

  1. Ionization type (air)
  2. Geiger-Muller (GM) type (Neon and Halogen) and
  3. Scintillation detector type [ NaI(Tl), ZnS
    (Ag)]

The choice of detector is depend on the type of radiation going tomeasure, energy, and quantity to be measured. The above mentionedtype survey meters are available in portable meters with capable ofmeasuring radiation count rate in mR/hr or R/hr. other devices forarea monitoring are Gamma Zone Monitor and door way mounted metersetc.

IonizationChamber Survey Meter:

Ionizationchamber consists of outer cylinder (cathode) coated inside withgraphite to make ti conducting and a central electrode (anode)insulated from the chamber wall as shown in the figure. Either air orgas will be used as an interacting medium and a suitable voltage isapplied across the electrodes. When the chamber is exposed toradiation, the radiation produces the ionization by interacting withthe gas or air inside the chamber. The movement of ions produces anelectric current in the outer electronic circuit of the chamber. Thestrength of this current is proportional to the number of ionizationevents caused by the energy absorbed in the air chamber and willserve as a measure for find the exposure rate or dose rate.

Radiation Protection (11)

Figure shows the circuit diagram of ion chamber based meters.

Number of ionizations produced in the detector is directlyproportional to the energy dissipated in the medium. Therefore,energy discrimination is possible with ionization chamber for heavilycharged particles by pulse height analysis. Ionization chambers areused whenever accurate measurements are required. They approximatethe condition under which the roentgen is defined. Ion chambers areused to measure outputs of x-ray machine, valuation of radiationlevels in brachytherapy, radionuclide therapy patients, and wards andto survey the radioactive material packages.

Ionchamber are capable of monitoring higher radiation exposure ratelevels and available in different ranges: 0-5 mR/hr, to 0-50R/hr.

GMType Survey Meters:

InGM survey meter operating voltage in the range of 500V -1300V appliedbetween the anode and the cathode of a chamber, which is filled witha gas of low electron attachment coefficient (argon and neon). Theelectrons produced in the chamber will have sufficient energy toproduce secondary and tertiary ionization during their accelerationtowards anode. This results in an amplification of ionization eventsin the chamber. This is known as gas avalanche which depends on thenature of gas and the pressure of gas. Hence, the whole wire iscovered by a sheath of electrons. The gas amplification isindependent of energy and type of radiation. Halogens are used asquenching gas in GM based type Survey meters.

GMmeters are pulsed in nature, they should be used only in X or Gammaphotons of continuous radiation. They should not be used in X-rayunits, which emit pulsed x-ray units such as Linear Accelerators.

Advantagesof GM Survey Meter:

  1. It is very sensitive and useful for monitoring for low levelradiation especially in nuclear medicine department.
  2. GM type instruments rugged and less costly.
  3. GM type meters are mainly used as radioactive contamination monitorwith thin window of 1.5mg/cm2, and large surface area.Contamination monitor is shown below in the diagram.

Radiation Protection (12)

Disadvantageof GM survey meter is long dead time (100micro sec) and result inloss of 20% of counts in 100,000 cpm measurements. GM survey metersshould not be used un high level radiation fields or when accurateexposure rates are required.

Questions:

  1. What are the quenching gases used in GM based survey meters?
  1. Halogens
  2. Inert gases
  3. Air
  4. All

2. Energy discrimination is possible in,

  1. GM based survey meters
  2. Ion chamber based meters
  3. Scintillating based meters
  4. All

Answer:

  1. Halogens
  2. ion chamber based meters

References:

  1. Text book of Radiological Safety, by Prof. K. Thayalan
  2. www.aerb.gov.in
  3. http://www.yorkphysics.com

Primary Barrier

Primary barrier is the barrier in which the primary beam of thetreatment machine falls (Linac, co-60 units) on it. The thickness ofthe primary is greater than the other barriers of room. Shieldingmaterials for primary barrier as well as other barriers are same likeconcrete, lead, and steel etc.

Primarybarrier thickness determination:

Therequired attenuation of the barrier B may be found according to adesired dose constraint that is derived from an occupational orpublic dose limit. Reference (1) uses the following expression todetermine the attenuation required by the barrier.

Radiation Protection (13)

Where,

P –is the allowed dose per week (Sv/week)outside the barrier.

D –is the distance from the isocentre to the outside of the barrier, inmeters.

SAD– Source to Axis Distance in meters

W –is the workload, in Gy/week at 1meter.

U –is the use factor or fraction of time that the beam is likely to beincident on the barrier.

T –is the occupancy factor or the fraction of time that the area outsidethe barrier is likely to be occupied (mentioned in the table 1)

Thethickness of concrete required from attenuation graphs, or by the useof TVLs. The number of TVLs required to produce this attenuation isdetermined from:

Radiation Protection (14)

Thewidth of the primary will be calculated as follows,

Theprimary barrier width is made equal to the maximum to the maximumfield size at the barrier plus 1foot (0.305m) on either side toprevent radiation from leaking through the secondary barrier thatabuts the primary. Most of the linear accelerator has 40cm x 40cm asmaximum field size at one meter from the target.

Whenthe collimator is rotated to 45 degree, the above dimension becomesequal to its diagonal (56.6cm) then the horizontal barrier width (W)required is given by

W =0.556d+ (0.305 x 2)

Where,d is the distance from the source to the barrier.

Questions:

  1. Calculate the primary barrier thickness of Co-60 unit. One TVL(density 2350 kg/m3)is 21.8 cm. permissible dose (p) =0.12mSv/week, distance (d) = 3meter, use factor (U) = 0.25,occupancy factor (T) = 1 and workload of the machine is 384 x 103mGy/week.
  1. 1033mm
  2. 103mm
  3. 1000mm
  4. 950mm

Answer:

  1. 1033mm

References:

  1. safety Report Series No. 47, IAEA, Vienna:2006
  2. the Textbook of Radiological Physics, by Prof. K. Thayalan.
  3. Atomic Energy Regulatory Board lecture notes.

Secondary Barrier

Secondary barriers are the barrier in which the secondary beam willfall on it. However, it is not facing the primary radiation we needto shield against the scattered radiation as well as leakageradiation from the head. Shielding materials used for the secondarybarrier is same as the primary barrier only example concrete, lead,and steel etc.

Internationalprotocol for the leakage radiation from the head of the linearaccelerator must not exceed 0.5% of the primary beam, outside theuseful beam at one meter from the path of the electron between thegun and target window and averaged over 100cm3. In theplane of the patient, the leakage must not exceed an average of 0.1%and it would be reasonable to assume this value when determining therequired secondary barrier thickness.

Therequired attenuation (BL) to shield against leakageradiation is as follows:

Radiation Protection (15)

Where,

P- is the design dose limit.

Ds- is the distance from the iso-centre to the point of interest inmeter.

W- is the workload.

T– is the occupancy factor.

Theuse factor for the secondary barrier is always considered as 1 forthe determining protection, because of that no need to write in theequation. In this case dsshould be measured from the gun end of the wave guide to the pointjust outside this barrier since this barrier will be subjected toleakage radiation from the vicinity of the gun.

Barrierthickness to shield against scattered radiation:

Therequired barrier transmission (Bp)needed to shield against radiation scattered by the patient.

Radiation Protection (16)

Where,

P,W and T have the same meaning as in the leakage radiation equation.

dsca– is the distance from the radiation source to the patient, inmeter

dsec– is the distance from the patient to the point of interest, inmeter

a- is the scatter fraction defined at dsca.The scatter primary ratio (a) is dependent on the energy of the X raybeam and the scattering angle. These data re tabulated per 400 cm2of irradiated field area for Co60, 6,10, 18, and 24 MV X ray beams.

F– is the field area incident on the patient , in cm2

Scatteredradiation from the patient or phantom is usually less than 0.1% ofthe incident radiation per 0.1 m2area irradiated. For larger scatter angles, the energy of thescattered radiation will be degraded.

Ifthe thickness required protecting from leakage differs from thatrequired to protect from scatter by less than one TVL, use thegreater thickness and add one HVL of shielding material for theenergy of the leakage radiation. If the two thicknesses for leakageand scatter protection differ by more than one TVL use the greaterthickness.

Questions:

  1. What will be the thickness of the secondary barrier ifthe leakage and scattered radiation barrier transmission valuediffers by one TVL,

  1. Use the greater thickness and add it one HVL
  2. Use the greater thickness and add it two HVL
  3. Use the lesser thickness
  4. All

Answer:

  1. Use the greater thickness and add it one HVL

References:

  1. Safety Report Series no. 47, IAEA, Vienna
  2. The Textbook of Radiological Physics, by Dr. K.Thayalan.

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