OCCUPATIONAL RADIATION SAFETY IN

RADIOTHERAPY

DEPARTMENT OF RADIOTHERAPY

CHRISTIAN MEDICAL COLLEGE, VELLORE

Timothy Peace S

PRESENTATION OUTLINE

• INTRODUCTION

• POTENTIAL AREAS OF RADIATION HAZARDS IN RT

• TELETHERAPY

– TELECOBALT

– MEDICAL LINEAR ACCELERATOR

• BRACHYTHERAPY

• GENERAL RADIATION SAFETY MEASURES

• RECOMMENDATIONS

INTRODUCTION

• Radiation therapy aims to

– Destroy the cancer

– using gamma rays, high-energy x-rays electrons, protons and heavy ions

– generated from radioisotopes, medical linear accelerators and synchrotrons

• Double-edged sword

– The cancer destroying radiation can also destroy normal cells

– Deterministic effects

• Gastrointestinal syndrome, CNS syndrome, cataract, pneumonitis, sterility, erythema, alopecia, cataract

– Stochastic effects

• Radiation carcinogenesis and genetic effects

POTENTIAL AREAS OF RADIATION HAZARDS IN RT

• Teletherapy

– Telecobalt treatment unit (1.25 MeV, gamma photons)

– Medical linear accelerator (6 & 15 MV high energy x-ray photons), electrons ranging from 4-21 MeV and neutrons arising from linear accelerators delivering more than 10 MV x-ray photons)

• Brachytherapy

– Pre-loaded system

– Manual after-loading system (only low dose rate brachytherapy)

– Remote after-loading system (also high dose rate brachytherapy)

• Simulator

– Diagnostic x-ray-based simulator unit

* The whole body dose limit is 20 mSv a year when averaged over 5 years with a maximum of 30 mSv in any one year (AERB)

Source: International Commission on Radiological Protection 26

Tissue or Organ Radiation Worker Member of Public

Whole of body 20* mSv /yr 1 mSv /yr

Lens of eye 150 mSv /yr 15 mSv /yr

Skin 500 mSv/yr 50 mSv /yr

Hands and feet 500 mSv /yr 50 mSv /yr

Pregnancy once declared

2 mSv to lower trunk

(1 mSv to foetus)

Foetus is considered to be member of public

ANNUAL DOSE LIMITS

TELETHERAPY TELECOBALT UNIT

• Potential Hazard 1: Source stuck during treatment

– Emergency situation when the Cobalt-60 source gets stuck in between the “off” and “on” position

– Potential Occupational Exposure: The radiographer has to enter the treatment room to push the source back

• Steps for minimizing exposure:

• Ask the patient (via intercom) to come out

– If not possible, enter from maze wall side (TLD badge must be worn)

– Rotate gantry to side opposite to maze wall

– Insert “T-rod” and push it till the source reaches “safe” position

TELETHERAPY TELECOBALT UNIT

Potential Hazard 2: Telecobalt Source transfer

– Replacement of Co-60 source

• Removal of old source

• Insertion of new source

– Occupational exposure during transfer

• Steps for minimizing exposure:

– Plan the procedure, minimize time and limit personnel

– Wear TLD badge and pocket dosimeter

– Monitor dose level using survey meter

Aligned with the machine head, “T-rod “used to exchange the source drawers

TELETHERAPY TELECOBALT UNIT

Potential Hazard 3: Dismantling without Decommissioning

– The telecobalt unit is dismantled or scrapped without decommissioning the unit (AERB-approved procedure for removal and disposal of source)

Case Study: Goiânia, Brazil • 1985: Private radiotherapy clinic

closed down

• 1375 Ci – Cs -137 teletherapy

machine abandoned

• 1987: teletherapy head stolen

• Unit dismantled, source capsule

ruptured causing major

contamination

• 249 people contaminated

• 0.1 - 6.2 Gy (6200 mSv)

• Permissible limit: 1 mSv for public

• 4 people died

CASE STUDY: SAMUT PRAKARN,THAILAND

• October 1999: 3 disused teletherapy sources stored by a private company at unsecured parking lot

• Jan/Feb 2000: unauthorized removal of one unit - dismantled for scrap

• 425 Ci - cobalt-60 source unshielded • 10 people highly exposed • 3 of whom died

Steps for avoiding this radiation disaster: • Proper decommissioning procedure

• Proper removal of source • Survey, contamination check & documentation • Disposal of source • Each step approved by regulatory body

TELETHERAPY – MEDICAL LINEAR ACCELERATOR

• The linear accelerator does not consist of a radioactive

source and hence poses a lesser radiation hazard

• It generates high energy electrons (4-21 MeV) and x-rays

(6-15MV)

• Potential hazard: Personnel entering the room when the

radiation is „on‟ can potentially receive lifetime dose in a

single exposure

• Case study: St Teresa’s Hospital (STH), Hong Kong – Two physicists performed quality assurance check on a medical

linac

– discovered the accidental presence of a female ward assistant

– through the room's CCTV

– As for the affected female staff received 70 Sv (very low)

TELETHERAPY –LINEAR ACCELERATOR

• Case study: Industrial Accelerator – 15 MV food irradiation facility in Hanoi. – An individual entered the irradiation room without the operators‟

knowledge – unwittingly exposed his hands to the x-ray beam. – The individual received doses

• 10 - 25,000 mSv to the left hand • 20 - 50,000 mSv to the right hand.

– Within one month one hand had to be amputated as well as the fingers on the other hand.

• Simple steps that could have avoided these unnecessary exposures – Console to face treatment room door – Door interlock – “Last man out” switch – Check CCTV before starting exposure

Limit for hand: 500 mSv

BRACHYTHERAPY

• Method of treatment in which the sealed radioactive sources are used to deliver high radiation at short distance

• Pre-loading or “Hot” loading

– Radioactive sources loaded in the applicators which are then inserted into the patient

– High occupational dose to personnel

– Dr Cyril Jayachandran developed a remote-controlled trolley to transfer the source to the „radium theater‟

– Now an obsolete technique

– Replaced by manual and remote afterloading systems

BRACHYTHERAPY - MANUAL AFTERLOADING

• Case study from another country:

Mishandling of source ribbons

– Patient scheduled for endobronchial

implant

• Ir 192 seeds: Activity- 2516 MBq.

– Staff mistakenly gave the attending

physician the inactive end of source

ribbon who inserted it into patient.

– Staff, assumed pieces of ribbon

contained no radioactive material,

coiled them and held them in her

hands.

– Dose to the staff‟s hand

• ~2.7 Gy (~2700 mSv – Allowed

500 mSv),

HDR BRACHYTHERAPY

• Case study from another country: Malfunction of high dose rate equipment – Patient was to be treated with a HDR

containing 159 GBq of Ir192

– The source wire had been broken and the source had remained in the patient.

– Personnel disregarded the alarm from an area radiation monitor because the unit console indicated 'safe'.

– The source remained in the patient for almost four days and the patient received 16,000 Gy at 1cm (Prescription: 18 Gy)

– The patient died shortly after removal of the source

– The loss of the source resulted in radiation exposure to 94 individuals

• Persons at the cancer clinic and the nursing home,

• Ambulance staff and workers at the waste disposal company

GENERAL RADIATION SAFETY MEASURES

• Area Monitor

– Gamma zone monitor for telecobalt and brachytherapy installations

• Personnel Monitoring

– TLD, pocket dosimeters

– OSLD

• Audio-visual system

• Door interlocks

GENERAL RADIATION SAFETY MEASURES

• “Last man out” switch

– First in India (2005)

• Emergency Buttons

• Radiation warning symbols

SURVEY OF HDR ROOM AND UNIT

DISCUSSION

• History shows that accidents rarely occur due to a single

equipment failure or a single human error. In most accident

cases there was a combination of elements such as:

– a) no prior safety assessment

– b) poor education and lack of training, especially when faced

with an unusual situation,

– c) management pressure (real or perceived) to continue work

even when safety systems were inoperable or deficient,

– d) poor maintenance programme or none at all, leading to a

reduction in layers of safety, and non-investigated false

alarms leading to persons ignoring warning systems.

RECOMMENDATIONS

• Each radiation professional in RT must cooperate with the Radiation Safety Officer to ensure

– Effective organisation of all radiotherapy practice

– Education, training and awareness

– Communication

– Follow-up of equipment faults

– Frequent Quality assurance

– General radiation safety measures (Area and personnel monitoring, routine survey, audio-visual system, safety interlocks and warning symbols)

– AERB guidelines must be followed for installation, commissioning and decommissioning of radiotherapy equipment

– AERB approved procedure for procurement, replacement and disposal of sources

– This will enable each radiation worker to handle radiation in a safe environment and limit the occupational exposure to “As Low as Reasonably Achievable - ALARA”

ACKNOWLEDGEMENTS

• Dr I Rabi Raja Singh, Radiation Safety Officer, CMC, Vellore

• Mr Jose Solomon Raj, Medical Physics Intern

• Mr Mohamathu Rafic, Lecturer in Medical Physics

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