This document discusses the design of shielding for X-ray rooms. It covers topics such as equipment design standards, using dose constraints in design, barriers and protective devices. The key aspects of shielding design are the type of X-ray equipment, its usage, positioning, number of tubes, and the occupancy of surrounding areas. Design involves calculating the dose at specific points and factors such as use, occupancy, and workload. Continuous integrity of shielding materials is important to prevent radiation leakage. Records of shielding design and inspections should be maintained.
Radiation is energy that is given off by particular materials and devices.
Radiation protection, also known as radiological protection, is defined by the International Atomic Energy Agency (IAEA) as "The protection of people from harmful effects of exposure to ionizing radiation, and the means for achieving this". Exposure can be from a source of radiation external to the human body or due to internal irradiation caused by the ingestion of radioactive contamination
Radiation is energy that is given off by particular materials and devices.
Radiation protection, also known as radiological protection, is defined by the International Atomic Energy Agency (IAEA) as "The protection of people from harmful effects of exposure to ionizing radiation, and the means for achieving this". Exposure can be from a source of radiation external to the human body or due to internal irradiation caused by the ingestion of radioactive contamination
Cavity theory.. Radiotherapy..
I explained about Bragg-gray, Spencer attix and Burlin theory..
In future I'll try to explain this with some more points. So wait for the updation.
I referred Radiation oncology (IAEA) book and
Introduction to Radiological Physics and Radiation Dosimetry by Frank Herbert Attix book
Sharing about “A typical day in the life as Radiation Therapy Technologist (RTT)” includes their roles, responsibilities, duties, working protocols, management, working stress, daily challenges in this modern radiotherapy era. As well as a bit information about how to become a RTT in India.
brief but informative knowledge about what basically LINAC is and what is the phenomenon behind this machine ... easy to understand as well as presenting during lectures and in classes . share it
Produces radiation that is referred to as a high-energy x-ray for patients with cancer In 1928, RWideroe demonstrated that electrons could be accelerated through a tube by applying a radio frequency voltage to sections of the tubeThe linear accelerator is an extension of Wideroe’s ideaThe name ‘linear accelerator’ comes from the fact that electrons are produced in the machine and accelerated in a straight line.
Cavity theory.. Radiotherapy..
I explained about Bragg-gray, Spencer attix and Burlin theory..
In future I'll try to explain this with some more points. So wait for the updation.
I referred Radiation oncology (IAEA) book and
Introduction to Radiological Physics and Radiation Dosimetry by Frank Herbert Attix book
Sharing about “A typical day in the life as Radiation Therapy Technologist (RTT)” includes their roles, responsibilities, duties, working protocols, management, working stress, daily challenges in this modern radiotherapy era. As well as a bit information about how to become a RTT in India.
brief but informative knowledge about what basically LINAC is and what is the phenomenon behind this machine ... easy to understand as well as presenting during lectures and in classes . share it
Produces radiation that is referred to as a high-energy x-ray for patients with cancer In 1928, RWideroe demonstrated that electrons could be accelerated through a tube by applying a radio frequency voltage to sections of the tubeThe linear accelerator is an extension of Wideroe’s ideaThe name ‘linear accelerator’ comes from the fact that electrons are produced in the machine and accelerated in a straight line.
Web Strategy Plus provides a “one stop shop” for all your print to web marketing needs. Our staff has a combined 30 plus years experience in design and marketing. We are committed to delivering exceptional customer service and affordable marketing solutions to meet your goals. Our home office is based in Cincinnati, OH but we work with companies across the globe. Whether you require a professional website or need help promoting it, we can help you with it all. Our main goal is to provide cost effective web strategies that drive results.
Learn how to search engine optimize your profile, get more recommendations, develop a targeted content strategy, automate your posts, monitor and engage with keyword targeted conversations.
Radiography Testing for Btech metallurgical and materirials science engineeringshyamkumarrakoti1
Radiography Testing for Btech metallurgical and materirials science engineering which is usefull in the field of non destructive testing methods this is one the of the non destructive testing method
Overview of Integrated Detector Electronics products including Application Specific Integrated Circuits, ROICs and low noise amplifiers for radiation detection.
Operation “Blue Star” is the only event in the history of Independent India where the state went into war with its own people. Even after about 40 years it is not clear if it was culmination of states anger over people of the region, a political game of power or start of dictatorial chapter in the democratic setup.
The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
Introduction to AI for Nonprofits with Tapp NetworkTechSoup
Dive into the world of AI! Experts Jon Hill and Tareq Monaur will guide you through AI's role in enhancing nonprofit websites and basic marketing strategies, making it easy to understand and apply.
Model Attribute Check Company Auto PropertyCeline George
In Odoo, the multi-company feature allows you to manage multiple companies within a single Odoo database instance. Each company can have its own configurations while still sharing common resources such as products, customers, and suppliers.
Synthetic Fiber Construction in lab .pptxPavel ( NSTU)
Synthetic fiber production is a fascinating and complex field that blends chemistry, engineering, and environmental science. By understanding these aspects, students can gain a comprehensive view of synthetic fiber production, its impact on society and the environment, and the potential for future innovations. Synthetic fibers play a crucial role in modern society, impacting various aspects of daily life, industry, and the environment. ynthetic fibers are integral to modern life, offering a range of benefits from cost-effectiveness and versatility to innovative applications and performance characteristics. While they pose environmental challenges, ongoing research and development aim to create more sustainable and eco-friendly alternatives. Understanding the importance of synthetic fibers helps in appreciating their role in the economy, industry, and daily life, while also emphasizing the need for sustainable practices and innovation.
How to Make a Field invisible in Odoo 17Celine George
It is possible to hide or invisible some fields in odoo. Commonly using “invisible” attribute in the field definition to invisible the fields. This slide will show how to make a field invisible in odoo 17.
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
Biological screening of herbal drugs: Introduction and Need for
Phyto-Pharmacological Screening, New Strategies for evaluating
Natural Products, In vitro evaluation techniques for Antioxidants, Antimicrobial and Anticancer drugs. In vivo evaluation techniques
for Anti-inflammatory, Antiulcer, Anticancer, Wound healing, Antidiabetic, Hepatoprotective, Cardio protective, Diuretics and
Antifertility, Toxicity studies as per OECD guidelines
Acetabularia Information For Class 9 .docxvaibhavrinwa19
Acetabularia acetabulum is a single-celled green alga that in its vegetative state is morphologically differentiated into a basal rhizoid and an axially elongated stalk, which bears whorls of branching hairs. The single diploid nucleus resides in the rhizoid.
1. IAEA
International Atomic Energy Agency
RADIATION PROTECTION IN
DIAGNOSTIC AND
INTERVENTIONAL RADIOLOGY
L12: Shielding and X Ray room design
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
2. IAEA 12: Shielding and X Ray room design 2
Introduction
• Subject matter: the theory of shielding
design and some related construction
aspects.
• The method used for shielding design and
the basic shielding calculation procedure
3. IAEA 12: Shielding and X Ray room design 3
Topics
Equipment design and acceptable safety
standards
Use of dose constraints in X Ray room design
Barriers and protective devices
4. IAEA 12: Shielding and X Ray room design 4
Overview
• To become familiar with the safety
requirements for the design of X Ray
systems and auxiliary equipment, shielding
of facilities, and relevant international safety
standards, e.g., IEC.
5. IAEA
International Atomic Energy Agency
Part 12: Shielding and X Ray room
design
Topic 1: Equipment design and acceptable
safety standards
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
6. IAEA 12: Shielding and X Ray room design 6
Purpose of Shielding
• To protect:
• the patients (when not being examined)
• the X Ray department staff
• visitors and the public
• persons working adjacent to or near the X Ray
facility
7. IAEA 12: Shielding and X Ray room design 7
Radiation Shielding - Design
Concepts
• Data required include consideration of:
• Type of X Ray equipment
• Usage (workload)
• Positioning
• Whether multiple tubes/receptors are being
used
• Primary beam access (vs. scatter only)
• Operator location
• Occupancy of Surrounding areas
8. IAEA 12: Shielding and X Ray room design 8
Shielding Design (I)
Equipment
• What equipment is to be used?
• General radiography
• Fluoroscopy (with or without radiography)
• Dental (oral, cephalometric, or OPG)
• Mammography
• CT
9. IAEA 12: Shielding and X Ray room design 9
Shielding Design (II)
The type of equipment is very important for
the following reasons:
• where the X Ray beam will be directed
• the number and type of procedures performed
• the location of the radiographer (operator)
• the energy (kVp) of the X Rays
10. IAEA 12: Shielding and X Ray room design 10
Shielding Design (III)
Usage
• Different X Ray equipment have very
different usage.
• For example, a dental unit uses low mAs
and low (~70) kVp, and takes relatively few
X Rays each week
• A CT scanner uses high (~130) kVp, high
mAs, and takes very many scans each
week.
11. IAEA 12: Shielding and X Ray room design 11
Shielding Design (IV)
• The total mAs used each week is an
indication of the total X Ray dose
administered
• The kVp used is also related to dose, but
also indicates the penetrating ability of the X
Rays
• High kVp and mAs means that more
shielding is required.
12. IAEA 12: Shielding and X Ray room design 12
Shielding Design (V)
Positioning
• The location and orientation of the X Ray
unit is very important:
• distances are measured from the equipment
(inverse square law will affect dose)
• the directions the direct (primary) X Ray beam
will be used depend on the position and
orientation
13. IAEA 12: Shielding and X Ray room design 13
Radiation Shielding - Typical Room
Layout
A to G are points
used to calculate
shielding
14. IAEA 12: Shielding and X Ray room design 14
Shielding Design (VI)
Number of X Ray tubes
• Some X Ray equipment may be fitted with
more than one tube
• Sometimes two tubes may be used
simultaneously, and in different directions
• This naturally complicates shielding
calculation
15. IAEA 12: Shielding and X Ray room design 15
Shielding Design (VII)
Surrounding areas
• The X Ray room must be designed with
knowledge of the location and use of all
rooms which adjoin the X Ray room
• Obviously a toilet will need less shielding
than an office
• Obtain a plan of the X Ray room and
surroundings (including level above and
below)
16. IAEA 12: Shielding and X Ray room design 16
Radiation Shielding - Design Detail
Must consider:
• appropriate calculation points, covering all
critical locations
• design parameters such as workload,
occupancy, use factor, leakage, target dose
(see later)
• these must be either assumed or taken from
actual data
• use a reasonable, worst case scenario
(conservatively high estimates), since under-
shielding is worse than over-shielding
17. IAEA
International Atomic Energy Agency
Part 12: Shielding and X Ray room
design
Topic 2: Use of dose constraints in
X Ray room design
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
18. IAEA 12: Shielding and X Ray room design 18
Radiation Shielding - Calculation
• Based on NCRP Report No 147, Structural
Shielding Design for Medical X-Ray Imaging
Facilities (2004)
• Assumptions used are conservative, so over-
shielding is common
• Software is available, giving shielding in thickness
of various materials
19. IAEA 12: Shielding and X Ray room design 19
Radiation Shielding Parameters (I)
P - design dose per week
• usually based on 5 mSv per year for
occupationally exposed persons (25% of
dose limit), and 1 mSv for public
• occupational dose must only be used in
controlled areas, i.e., for radiographers,
radiologists, and other radiation workers
20. IAEA 12: Shielding and X Ray room design 20
Radiation Shielding Parameters (II)
• Film storage areas (darkrooms) need
special consideration
• Long periods of exposure will affect film, but
much shorter periods (i.e., lower doses) will
fog film in cassettes
• A simple rule is to allow 0.1 mGy for the
period the film is in storage - if this is 1
month, the design dose is 0.025 mGy/week
21. IAEA 12: Shielding and X Ray room design 21
Radiation Shielding Parameters (III)
• Remember we must shield against three
sources of radiation
• In decreasing importance, these are:
• scattered radiation (from the patient)
• primary radiation (the X Ray beam)
• leakage radiation (from the X Ray tube)
22. IAEA 12: Shielding and X Ray room design 22
U - use factor
• fraction of time the primary beam is in a
particular direction i.e.: the chosen
calculation point
• must allow for realistic use
• for all points, sum may exceed 1
Radiation Shielding Parameters (IV)
23. IAEA 12: Shielding and X Ray room design 23
Radiation Shielding Parameters (V)
• For some X Ray equipment, the X Ray
beam is always stopped by the image
receptor, thus the use factor is 0 in other
directions, e.g., CT, fluoroscopy,
mammography
• For general radiographic and fluoroscopic
equipment the primary beam is usually
intercepted by the image detector
• This reduces shielding requirements
24. IAEA 12: Shielding and X Ray room design 24
Radiation Shielding Parameters (VI)
• For radiography, there will be certain
directions where the X Ray beam will be
pointed:
• towards the floor
• across the patient, usually only in one direction
• toward the chest Bucky stand
• The type of tube suspension will be
important, e.g.: ceiling mounted, floor
mounted, C-arm etc.
25. IAEA 12: Shielding and X Ray room design 25
Radiation Shielding Parameters (VII)
T - Occupancy
• T = fraction of time a particular place is occupied
by staff, patients or public
• Has to be conservative
• Ranges from 1 for adjacent offices and work areas,
to 1/20 for public toilets and 1/40 for outdoor areas
with transient traffic
26. IAEA 12: Shielding and X Ray room design 26
Occupancy (NCRP 147)
Area Occupancy
Work areas, offices,
staff rooms
1
Corridors 1/5
Toilets, unattended
waiting rooms
1/20
Outdoor areas with
transient traffic
1/40
27. IAEA 12: Shielding and X Ray room design 27
Radiation Shielding Parameters (VIII)
W - Workload
• A measure of the radiation output in one
week
• Measured in mA-minutes
• Varies greatly with assumed maximum kVp
of X Ray unit
• Usually a gross overestimation
• Actual dose/mAs can be estimated
28. IAEA 12: Shielding and X Ray room design 28
Workload (I)
• For example: a general radiography room
• The kVp used will be in the range 60-120 kVp
• The exposure for each film will be between 5 mAs
and 100 mAs
• There may be 50 patients per day, and the room
may be used 7 days a week
• Each patient may have between 1 and 5 films
SO HOW DO WE ESTIMATE W ?
29. IAEA 12: Shielding and X Ray room design 29
Workload (II)
• Assume an average of 50 mAs per film,
3 films per patient
• Thus W = 50 mAs x 3 films x 50 patients
x 7 days
= 52,500 mAs per week
= 875 mA-min per week
• We could also assume that all this work
is performed at 100 kVp
30. IAEA 12: Shielding and X Ray room design 30
Examples of Workloads
Weekly Workload (W) mA-min at:
100 kVp 125 kVp 150 kVp
General Radiography 1,000 400 200
Fluoroscopy (including spot films) 750 300 150
Chiropractic 1,200 500 250
Mammography 700 at 30 kVp (1,500 for breast
screening)
Dental
6 at 70 kVp (conventional intra-oral
films)
For more realistic values and CT see NCRP 147
31. IAEA 12: Shielding and X Ray room design 31
Workload - CT
• CT workloads are best calculated from
NCRP 147
• Remember that new spiral CT units, or
multi-slice CT, could have higher workloads
• A typical CT workload is about 28,000 mA-
min per week
32. IAEA 12: Shielding and X Ray room design 32
Tube Leakage
• All X Ray tubes have some radiation leakage -
there is only 2-3 mm lead in the housing
• Leakage is limited in most countries to 1 mGy hr-1
at 1 meter, so this can be used as the actual
leakage value for shielding calculations
• Leakage is specified at the maximum rated
continuous tube current, which is about 3-5 mA at
150 kVp for most radiographic X Ray tubes
33. IAEA 12: Shielding and X Ray room design 33
Radiation Shielding Parameters
34. IAEA 12: Shielding and X Ray room design 34
Room Shielding - Multiple X Ray
Tubes
• Some rooms will be fitted with more than
one X Ray tube (maybe a ceiling-mounted
tube, and a floor-mounted tube)
• Shielding calculations MUST consider the
TOTAL radiation dose from the two tubes
35. IAEA
International Atomic Energy Agency
Part 12: Shielding and X Ray room
design
Topic 3: Barriers and protective devices
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
36. IAEA 12: Shielding and X Ray room design 36
Shielding - Construction I
Materials available:
• Lead sheet brick
• gypsum or high Z plasterboard
• concrete block
• leaded glass or acrylic
37. IAEA 12: Shielding and X Ray room design 37
Shielding - Construction Problems
Some problems with shielding materials:
• Brick walls - mortar joints
• Use of lead sheets nailed to timber frame
• Lead inadequately bonded to backing
• Joints between sheets with no overlap
• Use of hollow core brick or block
• Use of plate glass where lead glass
specified
38. IAEA 12: Shielding and X Ray room design 38
Problems in shielding - Brick Walls &
Mortar Joints
• Bricks should be solid and not hollow
• Bricks have very variable X Ray attenuation
• Mortar is less attenuating than brick
• Mortar is often not applied across the full
thickness of the brick
39. IAEA 12: Shielding and X Ray room design 39
Problems in shielding - Lead
inadequately bonded to backing
• Lead must be fully glued (bonded) to a
backing such as wood or wallboard
• If the lead is not properly bonded, it may
peel off after a few years
• Not all glues are suitable for lead
(oxidization of the lead surface)
40. IAEA 12: Shielding and X Ray room design 40
Problems in shielding - Joins between
sheets with no overlap
• There must be 10 - 15 mm overlap between
adjoining sheets of lead
• Without an overlap, there may be relatively
large gaps for the radiation to pass through
• Corners are a particular problem
• Penetrations for electrical boxes and ducts
are of concern
41. IAEA 12: Shielding and X Ray room design 41
Problems in shielding - Use of plate
glass
• Leaded glass or acrylic should be used for
windows
• Laminated layers of plate glass can be used
where radiation levels are low, e.g., for the
wall at the foot of a CT scanner
42. IAEA 12: Shielding and X Ray room design 42
Radiation Shielding - Construction II
• Continuity and integrity of shielding very
important
• Problem areas:
• joints
• penetrations in walls and floor
• window frames
• doors and frames
43. IAEA 12: Shielding and X Ray room design 43
Penetrations
• “Penetrations” means any hole cut into the
lead for cables, electrical connectors, pipes
etc.
• Unless the penetration is small (~2-3 mm),
there must be additional lead over the hole,
Nails and screws used to fix bonded lead
sheet to a wall do not require covering
44. IAEA 12: Shielding and X Ray room design 44
Window frames
• The lead sheet fixed to a wall must overlap
any lead glass window fitted
• It is common to find a gap of up to 5 cm,
which is unacceptable
45. IAEA 12: Shielding and X Ray room design 45
Shielding of Doors and Frames
46. IAEA 12: Shielding and X Ray room design 46
Shielding - Verification I
• Verification of appropriate thickness and proper installation
is mandatory
• Two choices - visual or measurement
• Visual check (preferred) must be performed before
shielding covered - the actual lead thickness can be
measured easily
• Radiation measurement necessary for window and door
frames etc.
• Isotope source simplifies measurements
• Measurement for walls very slow
48. IAEA 12: Shielding and X Ray room design 48
Records
• It is very important to keep records of shielding calculations,
as well as details of inspections and corrective action taken
to fix faults in the shielding
• In 5 years, it might not be possible to find anyone who
remembers what was done!
• Shielding records should become a permanent part of the
facility engineering records; a copy should be stored in the
room (consider a permanent plaque on the wall in the room
specifying the amount of shielding in each wall); and a copy
should be retained by the medical physicist doing the
calculations
49. IAEA 12: Shielding and X Ray room design 49
Summary
• The design of shielding for an X Ray room is
a relatively complex task, but can be
simplified by the use of some standard
assumptions
• Record keeping is essential to ensure
traceability and constant improvement of
shielding according to both practice and
equipment modification
50. IAEA 12: Shielding and X Ray room design 50
Where to Get More Information (I)
• Radiation shielding for diagnostic X Rays.
BIR report (2000) Ed. D.G. Sutton & J.R.
Williams
• National Council on Radiation Protection
and Measurements, Report No. 147,
“Structural Shielding Design for Medical X-
Ray Imaging Facilities” Bethesda, MD 2004.
Editor's Notes
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to:
…
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)
Explanation or/and additional information
Instructions for the lecturer/trainer
Explanation or/and additional information
Instructions for the lecturer/trainer
Lecture notes: ( about 100 words)
Instructions for the lecturer/trainer
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to:
…
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)
A floor plan to a known scale, including not only the x-ray room, but also surrounding areas (including their function e.g. office, toilet, waiting room etc).
The location of the x-ray table and the type and orientation of the equipment.
The location of any upright bucky or chest stand (used to take X Rays of standing patients).
Details of what lies above, below and adjacent to the X Ray room, and the nature of the floor, wall and ceiling construction.
The distances from the X Ray tube and patient to points which are to be used in the calculations. Distance is denoted as d.
The target, or design, weekly radiation dose at each calculation point. This is called P.
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to:
…
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)
For many years, the method used for shielding design has been that described in the (American) National Council on Radiation Protection and Measurements (NCRP) Report 49. The data used in this report has usually resulted in overshielding, and the report is currently undergoing review. However, this document is currently the best reference available and for this reason, this module is based on NCRP 49
Each country has its own dose limits, but we will assume here that the values given in ICRP Report 60 (which are very widely used) apply. For occupationally exposed persons, the effective dose limit is 20 mSv per year. This averages to 0.4 mSv per week.
In addition, many countries are now applying an additional constraint in accordance with the ICRP 60 principle of optimisation of protection, on the basis that any one person could be exposed to more than one source of radiation
Anything which separates one area from another is called a barrier. Any barrier which may be in the direct X Ray beam is called a primary barrier. If the X Ray beam will never be directed towards a barrier, it is called a secondary barrier. In practice, some barriers will have the primary beam directed at them part of the time only, and the rest of the time they will be a secondary barrier. This must be taken into account in the calculations.
Once the type of barrier has been decided, the next factor to be determined is the use factor (U) (i.e. the proportion of time the beam may be pointed at that barrier). Use factors are usually assumed, but may be calculated for a particular case, based on actual operational information.
The occupancy factor (T) is an indication of how long a particular place or room may be occupied by an individual person. Thus an occupancy of 1 implies that the same person will spend all their working week in that place. Occupancy factors vary greatly, depending on the category of the area.
This table shows the standard NCRP 49 area categories and occupancy values.
To calculate correct shielding, we need to know the amount of work an X Ray unit does in a week. This is known as the workload (W) of the unit.
When considering workload, it is also important to know what kVp is used for the exposures. This is for two reasons: firstly, the mAs per exposure is lower for higher kVp, and secondly because the radiation is more penetrating as the kVp is increased.
NCRP 49 and many regulatory bodies have used quite high guidance values for usual workloads.
This table shows some of these values and the relevant kVp.It is now generally considered that these values are grossly inflated, particularly with modern radiographic film-screen systems which use very much less radiation than systems of 1976 when NCRP 49 was written. We also know, from recording actual workloads, that the kVp used is only occasionally greater than 100 kVp, and mostly around 90 kVp for a general radiography room. This concept of ‘workload spectrum’ will eventually be used in shielding calculations, but is not used here.
The distance from the X Ray tube to the scatterer (patient) is called dsca, the distance from the X Ray tube to a primary barrier is called dpri, and the distance from the scatterer to a secondary barrier is called dsec.
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to:
…
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)
The building materials available for shielding will vary according to the country. Some possibilities are:
Lead sheet bonded onto a solid backing such as plywood, compressed cement fibre board, particle board or similar.
Cement blocks - where used, they should preferably be solid, and care must be taken to ensure that the mortar joins carry through the full thickness of the blocks. As a rule of thumb, you can assume that a cement block is equivalent to at least 2/3 of its thickness in solid concrete.
Bricks may be used provided that they will give sufficient attenuation. Mortar joints must carry through the full thickness of the brick. Bricks vary greatly in their attenuation, therefore you must be careful when using this type of shielding.
Lead glass or lead acrylic for windows.
When advising on shielding materials it is often useful to know the comparative densities and lead equivalence of various materials, so that options can be considered.
The installation of the shielding should be supervised by someone with the appropriate knowledge. Even a weekly visit to the building site, and good communications with the builder can avoid problems, delays, and expensive alterations.
You have two options when it comes to being satisfied that the shielding has been correctly constructed - you verify it as it is being built or you verify it after it has been built.
You should never just assume that shielding is correct. It must always be checked.
Of these two options, verification during construction is by far the easiest. All that is required is a visit to the site at each stage before the shielding material is covered up. That way, you can easily see that the shielding is free of holes, is the correct height and the correct thickness, with sufficient overlap of materials. Windows should be checked before the join to wall shielding is covered. A very common fault is that a gap in the shielding is left around the window, sometimes as wide as 3 cm.
Verification after completion is laborious, inexact, and difficult.
Let’s summarize the main subjects we did cover in this session. (List the main subjects covered and stress again the important features of the session)