Radiation shielding is needed for megavoltage photon therapy machines to limit radiation exposure and reduce effective dose outside of treatment rooms. Approximately 50% of cancer patients receive radiation therapy. Shielding barriers like lead and concrete are used to reduce radiation levels in uncontrolled and controlled areas like corridors and waiting rooms based on factors like workload, use, and occupancy. Proper machine orientation and maze or direct door designs can further reduce dose near room entrances. Ducting and electrical routing must also consider radiation protection. Skyshine radiation from scattered photons above the treatment room requires special consideration in shielding design.

1. Radiation Shielding for
Megavoltage Photon Therapy
Machines
RADIATION
PROTECTION
1
Daryoush
khoramian

2. 2
The International Agency for Research on
Cancer(IARC) recently estimated that 7.6
million deaths worldwide were due to cancer
with 12.7 million new cases per year being
reported worldwide
Breast cancer in females and lung cancer in
males are the most frequently diagnosed cancers
( Freddie Bray et al 2011)
 Approximately 50% of all cancer patients will
receive radiation therapyradiation therapy during their course of
illness ( Basker et al 2012 )

3. Basic principles
 The purpose of radiation shielding :
To limit radiation exposures to members of the
public and employees to an acceptable level. (
NCRP report no.151 )
Areas
Uncontrolled areas  1 mSv/yr
Controlled areas  5 mSv/yr
NCRP,2007
NCRP,2007
3

4. The purpose of radiation shielding :
To reduce the effective equivalent dose from a linear accelerator to a point
outside the room to a sufficiently low level.
4
In radiation therapy rooms

5.  Workload
 Use factor
 Occupancy factor
Use factor
Walls 1/4
Floor 1/2
Ceiling 1/4 or 1/2
T
Full occupancy
Work areas, offices,
nurses’ stations
1
Partial occupancy
Corridors, restrooms, ..
1/4
Occasional occupancy
Waiting rooms,
stairways, …
1/6
Or
1/16
5

6. 6
Barriers

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8. 8

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TVL in 16
MV
TVL in 16
MV

14. 14
 It’s toxic
 lead is not self supporting  needs to be held in place
 Relatively transparent to neutrons but decrease energy of neutrons by inelastic scattering

15. 15

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19. 19

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Overall size
 The couch radius : 9’
 Back wall  end of couch : 21’
 22’×20’ clear area
 Height : 9’-10’

21. 21
Machine orientation
Parallel to
the maze
Orthogonal to
the maze Special design

22. 22
Maze vs. direct door
 Where the available space
is minimal
 Doors are Very heavy
( several tons )
 Very expensive
 In order to reduce the radiation dose near
the entrance
 Is a route for ventilation ducts and electrical
conduits

23. 23
Ducts

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Electrical cable

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Special Considerations

26. 26
Skyshine Radiations

27. 27
References :
1.Baskar, Rajamanickam, Lee, Kuo Ann, Yeo, Richard, & Yeoh, Kheng-Wei. (2012). Cancer
and radiation therapy: current advances and future directions. International journal of medical
sciences, 9(3), 193.
2.Biggs, Peter J. (2010). Radiation Shielding for Megavoltage Photon Therapy Machines:
Boston: sn.
3.Deye, James A, Rodgers, JE, Wu, RK, Biggs, PJ, McCall, RC, & McGinley, PH. (2005).
Structural Shielding Design and Evaluation from Megavoltage X-and Gamma-Ray Radiotherapy
Facilities. National Cancer Institute, Rockville, Maryland.
4.INTERNATIONAL ATOMIC ENERGY AGENCY, RADIATION PROTECTION IN THE
DESIGN OF RADIOTHERAPY FACILITIES, IAEA, Vienna (2005).
5.Khan, Faiz M, & Khan, FM. (2003). The physics of radiation therapy (Vol. 3): Lippincott
Williams & Wilkins Philadelphia.
6.Turner, James Edward, & Kelsey, Charles A. (1995). Atoms, radiation, and radiation
protection: Wiley New York.

28. Thank you
Any question ?