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Radiation protectionfor particle accelerators
Lars Hjorth Præstegaard, Ph.D.Technical managerMedical physicist
Aarhus University Hospital
Health physics
Aarhus University Hospital, Århus Sygehus
Dose quantities
Definition: Effective doseThe effective dose is given by
where wT is the weighting factor for tissue T and the sum is over all radiation quantities and tissues in the body (unit: Sv).
Definition: Absorbed doseThe absorbed dose D is the ratio of dε/dm where dε is the mean energy imparted by ionizing radiation to mass dm (unit: J/kg).
Definition: Radiation weighting factorThe radiation weighting factor wR is the biological effectiveness of radiation R relative to photons.
∑=TR
TRT DwwE,
Equivalent total body dose from photons
Aarhus University Hospital, Århus Sygehus
Dose quantities
20Alpha particles, fission fragments, heavy nuclei
5Protons, other than recoil protons, > 2 MeV
5> 20 MeV10> 2 to 20 MeV20> 0.1 to 2 MeV1010 to 100 keV5<10 keV
Neutrons:1Electrons and muons, all energies1Photons, all energies
Radiation weighting factor wR
Type and energyof radiation R
Aarhus University Hospital, Århus Sygehus
Dose quantities
1.00Whole body total
0.05Remainder
0.01Bone surface
0.01Skin0.05Thyroid
0.05Oesophagus
0.05Liver
0.05Breast
0.05Bladder
0.12Stomach0.12Lung
0.12Colon
0.12Bone marrow (red)
0.20Gonads
Tissue weighting factor wT
Tissue or organ
Aarhus University Hospital, Århus Sygehus
Why is radiation dangerous?
Ionizing radiation causesdamage to DNA:• Direct damage to the DNA.• Indirect damage: Creation of free
radicals that may damage the DNA.• If DNA is damaged, the cell is likely to
die when the cell divides.
Repair of damage:• Most of the damaged DNA is repaired
before the cell divides.• Double-strand breaks are more difficult
to repair than single strand breaks.• Incorrect repair (mutation) may cause
cancer.
Aarhus University Hospital, Århus Sygehus
Why is radiation dangerous?
Stochastic damage:• Incorrect repair or damage to the
DNA (mutation) which do not cause the cell to die.
• The stochastic damage may cause the cell to transform into a cancer cell after several years.
Deterministic damage:• Damage to tissue due to direct cell
death (e.g. radiotherapy)• Only observable for doses above
0.5 Gy. • The effect of radiation is observed
within a few weeks (acute).42 Gy / 12 fx
Aarhus University Hospital, Århus Sygehus
Why is radiation dangerous?Effects of acute whole body exposure:
Death after 24-48 hours100Death within a few weeks10
LD 50/30 (half of population death within 30 days)
4.5Probable recovery1No observable effect0.5
EffectDose (Gy)
Curative radiotherapy:35-80 Gy within a small region of the body
Aarhus University Hospital, Århus Sygehus
Why is radiation dangerous?
Linear fit: 5 % per Sv
Lifetime excess risk of death caused by cancer:
Aarhus University Hospital, Århus Sygehus
Dose to the publicContributions to the background radiation:
Average background radiation in Denmark: 3 mSv/year
Cancer deaths in Denmark due to background radiation: ~750/year3 mSv/year ~ 1 cigarette per day
Aarhus University Hospital, Århus Sygehus
Dose limits in the EC
Bekendtgørelse nr. 823 af 31. oktober 1997 om dosis-grænser for ioniserende stråling:
Dosisgrænserne for dosisovervåget arbejdstagere og enkeltpersoner i befolkningen er henholdsvis 20 mSv/år og 1 mSv/år.
Radiation from aparticle accelerator
Aarhus University Hospital, Århus Sygehus
Radiation from an electron accelerator
Electron beam + Matter
Photons:
Neutrons:
Neutron
NucleusPhoton
(γ,n) process
Induced radioactivity:1. (γ,n) process
neutron nucleus
Photon
2. Neutron capture
Bremsstrahlung (x-rays)
β-, β+
Photon
β-, β+
Aarhus University Hospital, Århus Sygehus
Radiation from an electron accelerator
Radiation Protection Dosimetry, Vol. 96, No 4, pp. 333–343 (2001)
Threshold for neutron production:Most materials: 6-13 MeV
However:9Be: 1.67 MeVD: 2.23 MeV16O: 15.67 MeV12C: 18.72 MeV
Dose equivalent rates per unit beam power:
Dose from forward bremsstrahlung dominates at all energies
Aarhus University Hospital, Århus Sygehus
Electron accelerator: PhotonsAngular distribution of bremsstrahlung (tungsten target):
Aarhus University Hospital, Århus Sygehus
Electron accelerator: Neutron production
Rule of thumb:Neutron yield largest in high-Z materials
Averrage neutron energy:1-2 MeV for medical electron accelerator
Angular distribution:Isotropically for high-Z materials
Neutron yield from a thick target:
IAEA Technical report, no. 188, 1979
present in and near the target in medical
electron accelerator
Aarhus University Hospital, Århus Sygehus
Radiation from a proton acceleratorHigh energy proton beam + Matter
Spallation process:
ProductionNeutronsPhotonsα particlesIonsInduced rad....
Neutron production by proton bombardment is the most significant radiation hazard for proton accelerators
Aarhus University Hospital, Århus Sygehus
Radiation from a proton accelerator
Radiation Protection Dosimetry, Vol. 96, No 4, pp. 393–406 (2001)
Thick-target neutron yield for protons/carbon ions:
Therapeutic carbon ions on:
: Cobber
: Carbon
Therapeutic protons on:
: Iron
: Soft tissue
Aarhus University Hospital, Århus Sygehus
Radiation from a proton acceleratorNeutron production in a proton accelerator (forward direction):
Radiation Protection Dosimetry (2005),Vol. 116, No. 1–4, pp. 245–251
1E-20
1E-19
1E-18
1E-17
1E-16
1E-15
1E-14
0 50 100 150 200 250
Proton energy (MeV)
Neu
tron
dos
e(S
v*m
^2 p
er p
roto
n)
CNAlFeCuW
Radiation Protection Dosimetry,Vol. 96, No. 4, pp. 381–392 (2001)
Aarhus University Hospital, Århus Sygehus
Induced radioactivity: Electron accelerators
Neutron
NucleusPhoton
(γ,n) process
Photon
β-, β+
neutron nucleus
Photon
Neutron capture
β-, β+
Induced radioactivity is mainly caused by:
Largest neutron production at locations with large beam loss
Only production of β-, β+, and γ emitters
Aarhus University Hospital, Århus Sygehus
Induced radioactivity: Electron accelerators
Radiation protection: Time and avoid areas of large beam loss
Low level of induced radioactivity + short lifetime
Induced radioactivity for a medical electron accelerator:
Only short-lived
nuclides
Aarhus University Hospital, Århus Sygehus
Induced radioactivity: Proton accelerators
Spallation process:
Many processes contribute to induced radioactivity:
Highest neutron production at locations with large beam loss
The problem of induced radioactivity is far more serious in proton accelerators than for electron accelerators(approximately a factor of 100!)
Only production of β-, β+, and γ emitters
Aarhus University Hospital, Århus Sygehus
Induced radioactivity: Proton accelerators
Radiation Protection Dosimetry (2007), Vol. 123, No. 4, pp. 417–425
Irradiation of samples 1.2 m below 12 GeV proton beam-line for 3 months (specific activity in Bq/g):
Aarhus University Hospital, Århus Sygehus
Induced radioactivity: Proton accelerators
Radiation Protection Dosimetry (2007), Vol. 123, No. 4, pp. 417–425
Half life of most important nuclides:
Aarhus University Hospital, Århus Sygehus
Induced radioactivity: Proton acceleratorsCERN activation limits for waste (nuclide specific):
Aarhus University Hospital, Århus Sygehus
Induced radioactivity: Proton accelerators
The gamma dose 1 m from the patient copper collimator after a single 2 min treatment session: 3.24 mSv/h (half-life of 23.4 min)
Example: Proton therapy
Shielding materials
Aarhus University Hospital, Århus Sygehus
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
0 5 10 15 20 25 30
Concrete depth (cm)
Rel
ativ
e ph
oton
dos
e
Shielding materials: PhotonsDefinition of TVL (tenth-value layer):
TVL
Attenuation length: (1/e reduction of dose) = TVL/ln(10)
Buildup region Exponential falloff of photon dose after the first few cm in concrete⇒The TVL formalism can be used
Aarhus University Hospital, Århus Sygehus
Shielding materials: Photons
27.221.03.84Ledite XN-240
22.217.14.80Ledite XN-288
1.5Earth (dry, packed)
131880.98Boron-loaded polyethylene
3.7-4.8Heavy concrete
5.65.711.35Lead10.89.97.80Steel
43.035.02.35Normal concrete
TVL, 15 MV(cm)
TVL, 6 MV(cm)
Density(g/cm3)
Large density provides good shielding
Primary photons from a medical electron accelerator:
Aarhus University Hospital, Århus Sygehus
Shielding materials: Neutron interactions
Fast neutrons (>0.5 eV):• Emitted in all direction from the source.• Neutron interactions energy loss):
– Elastic collisions:• Dominating interaction.• Billiard-like collisions.• Elastic collision with atomic nucleus ⇒ energy loss ⇒
conversion of fast neutrons to slow neutrons.– Hydrogen: Large energy loss per collision.– Lead: Low energy loss per collision.
– In elastic collisions: (n,2n), (n,p) and others• Dominates neutron energy loss for heavy nuclei.• (n,2n) process ⇒ increases the neutron fluence.
Concrete: at least ~5 % water (hydrogen) per weight
Aarhus University Hospital, Århus Sygehus
Shielding materials: Neutron interactions
Slow neutrons (<0.5 eV):• Most thermal neutrons (~0.025 eV).
• Neutron interactions:
– Elastic collisions with atomic nucleus.
– Neutron absorption:
• Capture of thermal neutrons in atomic nucleus: (n,γ) reaction.– Large cross section for capture in boron and cadmium.
– Emission of photons at capture (only 0.478 MeV photon for Boron).
• Few resonances in keV region.
Efficient neutron shielding:Boron-loaded polyethylene (hydrogen + boron)
Aarhus University Hospital, Århus Sygehus
Shielding materials: Neutrons
153.84Ledite XN-240
164.80Ledite XN-288
9.60.880.98Boron-loaded polyethylene
8841011.35Lead
3810.77.80Steel
21342.35Normal concrete
TVL, fast(cm)
TVL, slow(cm)
Density(g/cm3)
1. Hydrogen and boron provides a good shielding2. Concrete: TVL,neutron <TVL,photon
Neutrons from a medical electron accelerator (15 MV):
Aarhus University Hospital, Århus Sygehus
Shielding materials: Neutrons
Neutron transmission is exponential after a depth of 40 cm in concrete.⇒The TVL formalism can be used
Neutron transmission for 70 MeV protons in concrete (nitrogen target):
Radiation Protection Dosimetry (2005),Vol. 116, No. 1–4, pp. 245–251
Aarhus University Hospital, Århus Sygehus
Shielding materials: Neutrons
Neutron spectra are harder in forward directions for Proton energies > 30 MeV Radiation Protection Dosimetry (2005),
Vol. 116, No. 1–4, pp. 245–251
Attenuation length as a function of neutron emission angle:
targetmaterials
70 MeV protons 100 MeV protons
iron target
Concrete TVL ≈ 41 cm
Concrete TVL≈ 56 cm
Aarhus University Hospital, Århus Sygehus
Shielding materials: Neutrons
Radiation Protection Dosimetry,Vol. 96, No. 4, pp. 381–392 (2001)
Neutron production and attenuation length in concrete for 250 MeV protons:
Attenuation length of 110 g/cm2: Concrete TVL≈ 108 cm!!!
Neutron spectra are harder in forward directions for Proton energies > 30 MeV
Aarhus University Hospital, Århus Sygehus
Shielding materials: Neutrons
Radiation Protection Dosimetry (2005),Vol. 116, No. 1–4, pp. 245–251
Relative dose of neutrons in the forward direction for protons on a thick iron target:
Depth in concrete (cm)
Neutrons dominate the shielding design for proton energies above ~30 MeV(Neutron TVL>photon TVL)
Shielding of aparticle accelerator
Aarhus University Hospital, Århus Sygehus
Radiation from a medical electron acc.
1. Primary photons from target (treatment felt)
2. Scattered photons from patient and walls
3. Leakage radiation (leakage photons from the accelerator)
Photon sources from a medical accelerator:
secondaryphotons
Aarhus University Hospital, Århus Sygehus
Shielding: Primary/secondary barriers
DK legislation:Dose limit for shielding design: 1 mSv/year
Aarhus University Hospital, Århus Sygehus
Shielding: Workload (W)
Typical workloads for values for Medical electron accelerator:• Primary radiation:
– 6 MV: 500 Sv/week– 15 MV: 250 Sv/week
• Secondary radiation:– 6 MV: 3.6 Sv/week– 15 MV: 1.6 Sv/week
Definition:Dose 1 m from a source of radiation per working week (37 hours)
A workload is defined both for primary radiation and secondary radiation (scattered radiation)
Aarhus University Hospital, Århus Sygehus
Shielding: Workload (W)Workload for a largeaccelerator:
Many sources of radiation which depend on the beam loss pattern
Example: Proton therapy27 sources of radiation.
Aarhus University Hospital, Århus Sygehus
Shielding: Area occupancy factor (T)
1 (=full occupancy): Offices, treatment planning, control rooms, laboratories etc.
1/2: Adjacent treatment room.
1/5: Corridors, employee lounges, staff rest rooms etc.
1/8: Mace doors.
1/20: Public toilets, unattended waiting rooms, storage areas etc.
1/40: Outdoor area with only transient pedestrian or vehicular traffic, stairways, unattended elevators etc.
NCRP 151 recommendation for radiotherapy facilities:
Aarhus University Hospital, Århus Sygehus
Shielding: Beam orientation factor (U)Definition:Fraction of accelerator workload the radiation is directed towards a given barrier
Fixed beam accelerators:Single primary barrier for which U=1.
Accelerator with gantry:The sum of all use factors for each primary barrier is 1.
Secondary barriers:U=1 as the secondary barrier always protect against stray radiation regardlessof the beam direction.
Aarhus University Hospital, Århus Sygehus
Shielding: Primary photons
Reduction of dose behind shielding:• Workload (W) ↓ (½ Workload ⇒ ½ dose)• Occupancy (T) ↓ (½ Occupancy ⇒ ½ dose)• Distance (d) ↑ (2 × Distance ⇒ 1/4×dose)• Use factor (U) ↓ (½ Use factor ⇒ ½ dose)• Wall thickness (t) ↑ (1 TVL more ⇒ 1/10×dose)
pTVLtp
dWTU −102
Primary photon dose behind shielding:
Wp: Primary photon workloadd: Distance from primary photon source)
(Radiotherapy: distance from target)
Aarhus University Hospital, Århus Sygehus
Shielding: Leakage photons
leakTVLtp
dWTL −102
0
Leak photon dose behind shielding (large angle bremsstrahlung):
Leakage photons are assumed to be emitted isotropically with the same TVL in all directions: U=1
WL: Leak photon workloadL0: Fraction of leakage photonsd: Distance from leak photon source.
Application: Leak radiation from a medical electron accelerator:WL=0.001*Wd: distance from the isocenter.
The energy of leakage photons is lower than that of the primary beam (lsmaller TVL).
Aarhus University Hospital, Århus Sygehus
Shielding: Photons scattered on a surface
2w
p
dWUT ⋅⋅
Primary dose at surface:
Wp: Primary photon workloaddw: Distance from primary photon source to the surface.
Properties of scattered dose (far from surface):
Scattered dose ∝ Primary dose at surface ⋅ A/dr2
dr: Distance from scattering surface to point of interestA: Area of primary field on surface (m2)
Dose of scattered photons:
22rw
p
dA
dUWT α
Constant of proportionality: α = reflection coefficient A dr
Aarhus University Hospital, Århus Sygehus
Shielding: Photons scattered on a surface
Application: Photons scattered in the patient
2sec
2400
dFa
dWTU
sca
pWp: Primary photon workloaddsca: Distance from primary photon source to the patient.dsec: Distance from the patient to the point of interesta: Scatter fraction (depend on gantry angle)F: Field size at the patient (cm2)d: Distance from secondary photon source.
The energy of scattered photons are lower than those of the primary beam (lower TVL).
Dose of two photon scatterings:
22,
222
1,
112
rrw
p
dA
dA
dUWT αα
A1A2
dr,1
dr,2
Aarhus University Hospital, Århus Sygehus
Shielding: Neutrons
102d
TW neutronTVLtN
−
Concrete, Ledite:Neutron dose behind shielding can be ignored (neutron TVL< photon TVL)
Neutrons are assumed to be emitted isotropically with the same TVL in all directions: U=1 (not valid for proton energies above 30 MeV)
Neutron dose behind shielding:
d: Distance from neutron source
Aarhus University Hospital, Århus Sygehus
Shielding: Access to acceleratorDirect access:
• Entrance through secondary barrier.• Short distance from control room to accelerator.• Very thick, heavy door, and complex needed.• Malfunction of door: problem!
Direct access doors:
Aarhus University Hospital, Århus Sygehus
Maze: Access to accelerator
Maze:• Entrance through long corridor with one or more turns.• Purpose: Reduction of entrance door thickness.• Long distance from control room to accelerator.• Requires more space.
• Malfunction of door: Small problem.
• Widely used.
Aarhus University Hospital, Århus Sygehus
Maze: Scatter of primary photons in patientDose at the maze door from scatter of primary photons in the patient:
A2
d1
d2
∏=i
ii
sca
pp
id
AFad
WTUD 22 400 α
Wp: Primary photon workloada: Scatter fraction (depend on gantry angle)F: Field size at the patient (cm2)αi: Reflection coefficient for i'th scatteringAi: Area of i'th scattering surfacedi: Distance of i'th scattering leg
dsca
Aarhus University Hospital, Århus Sygehus
Maze: Scatter of primary photons
A1
A2d1
d2
∏=i i
ii
w
pw d
AdUWT
D 22α
Wp: Primary photon workloaddw: Distance from primary photo source to wallαi: Reflection coefficient for i'th scatteringAi: Area of i'th scattering surfacedi: Distance of i'th scattering leg
Dose at the maze door from scatter of primary photons at the walls:
Aarhus University Hospital, Århus Sygehus
Maze: Leakage photonsDose at the maze door from leak photons :
∏=i i
iipL d
AdWTL
D 220 α
Wp: Primary photon workloadL0: Fraction of leakage photonsd: Distance from leak photon sourceαi: Reflection coefficient for i'th scatteringAi: Area of i'th scattering surfacedi: Distance of i'th scattering leg
d1
d
A1
Aarhus University Hospital, Århus Sygehus
Maze: Transmission through maze wallDose at the maze door from head leakage through the maze wall:
20
t
pT d
BWLTD =
Wp: Primary photon workloadL0: Fraction of leakage photonsB: Transmission through the maze walldt: Distance from leak photon source to door
The transmission of photons scattered on the patient is ignored
Aarhus University Hospital, Århus Sygehus
Maze: Gamma capture photons
Photon spectrum:• Concrete: 0-8 MeV (average: 3.6 MeV)• Boron: 0.478 MeV
Boron in the maze decreases the capture gamma dose
Dose at maze door Neutron capture gamma radiation:
⇒
Aarhus University Hospital, Århus Sygehus
Maze: Scattered neutronsDose at maze door from scattered neutrons:
m 5
12
1
210 drNn S
AdWD −=
Reduction caused by bend + extra maze length
WN: Neutron workload Ar: Cross-sectional area of inner maze entrance (m2)S1: Cross-sectional area of maze (m2)
m 5m 5
12
1
32 103110 ddrN
n SA
dWD −−=
Maze without bend:
Maze with bend:
Aarhus University Hospital, Århus Sygehus
Maze: Total dose at maze door
Total dose at maze door for electron accelerators below 10 MeV:
MeV 10 ∑∑∑∑ +++=<
GT
GL
Gw
Gpd DDfDDD
Sum over all gantry angles GGantry rotation axis perpendicular to mazef: Patient transmission factor
If Dd>1 mSv/year a maze door with shielding is needed
Total dose at maze door for electron accelerators above 10 MeV:
Ncdd DDDD ++= <> MeV 10MeV 10
Dc: Capture gamma dose at maze door.Dn: Scattered neutron dose at maze door.
Aarhus University Hospital, Århus Sygehus
Shielding: Maze
Methods to reduce the dose at the maze entrance:• Long maze.• Long distance from accelerator to maze. • Narrow maze.• Many turns of maze:
– neutrons must scatter many times.• Boron in maze walls:
– Efficient capture of neutrons.– Soft gamma radiation from neutron capture.
• Thick maze door.
Aarhus University Hospital, Århus Sygehus
Shielding: Safety installations
Emergency stop button in the accelerator room:Press the emergency stop button if the accelerator start running while you are in the accelerator room.
”Last man out” button in the accelerator hall:Confirm you are the last person that leaves the accelerator room. If the button is not pressed immediately before closing the entrance door, the accelerator should be interlocked.
Example:Shielding of radiotherapy
electron accelerators:Accelerator 7 and 8
Aarhus University Hospital, Århus Sygehus
Layout
accelerator 8
accelerator 7
accelerator 3
Challenges: Limited footprint for treatment roomsThickness of ceiling shielding: 90 cm
Accelerator room 7 and 8 at Århus University Hospital (build in 2004)
Aarhus University Hospital, Århus Sygehus
Choice of shielding material
Limited footprint for treatment rooms:• Photons:
– Choose larger density than that of normal concrete.• Neutrons:
– Choose shielding material with large hydrogen content.– If possible also boron.– Steel and lead provides insufficient neutron shielding.
Problems with heavy concrete:• Slow hardening process. • Medium density only 3-4 g/cm3.
Solution: Ledite®
Aarhus University Hospital, Århus Sygehus
Ledite®
Ledite®:• Commercial product.• Concrete with iron and boron.• Pre-harded blocks.• High density:
– XN-240: 3.84 g/cm3.– XN-288: 4.80 g/cm3.
• Very fast building process (4-6 weeks per room).
Aarhus University Hospital, Århus Sygehus
Primary shielding
121.92
60.96
Ledite XN-288 wall
thickness(cm)
5.6
6.4
d(m)
0.10
0.10
U6
0.33
0.33
U18
1
1
T
0.4480Acc. 8
0.524110Acc. 3
Dose (mSv/year)
Number of Ledite XN-288 layers
Concrete thickness
(cm)Direction
Accelerator 7 :
Advantage of Ledite:Ledite XN-288: 122 cmNormal concrete: 236 cm
Aarhus University Hospital, Århus Sygehus
Primary shielding: Ceiling
92.1Total thickness (cm)82.35Normal concrete (floor)
60.964.80Ledite XN-2886.350.98Boron-loaded polyethylene15.2411.35Lead1.597.80Steel
Thickness(cm)
Density (g/cm3)
No shielding of neutrons
3-10 times larger hydrogen content
density than that of concrete (also boron)
Dose behind shielding: 0.27 mSv/year
Aarhus University Hospital, Århus Sygehus
Secondary shielding
0.51
0.32
0.22
0.08
0.06
Photon dose
(mSv/year)
0.05
0.01
0.01
0.00
0.00
Neutron dose
(mSv/year)
61.0
76.2
76.2
15.24
76.2
Ledite XN-240 wall thickness
(cm)
8.6
7.6
5.1
6.1
4.3
d(cm)
0.08251110Acc. 3
0.0601/160West
0.232810Acc. 8
1
1
T
30
0
θ(°)
0.56
0.33
Total dose(mSv/year)
0Control room
0East
Concrete thickness
(cm)Direction
Accelerator 7 :
Small contribution
Aarhus University Hospital, Århus Sygehus
Maze
5454Gamma radiation
9463161110Secondary photons through maze wall
178282336539Total for secondary photons
1498
55
52
77
18 MV
120
68
31
6 MV
Accelerator 8
2595Scattered primary photons
18 MV6 MV
26135Scattered leak photons
786
34
Neutrons
198Scattered primary photons in patient
Accelerator 7
Dose without maze door (μSv/week):
⇒ Maximum year dose reached within one week!
Aarhus University Hospital, Århus Sygehus
Maze
18.43Total0.64Steel4.45Lead
12.75 % boron-loaded polyethylene
0.64Steel
Thickness(cm)Material
Measured dose atmaze door:
Acc. 7: 1.22 mSv/year (measured: 0.48 mSv/year)Acc. 8: 0.74 mSv/year (measured: 0.29 mSv/year)
The maze has no turn⇒ Large dose from scattered x-rays and neutrons.⇒ Thick and heavy door needed:
Example:Shielding of radiotherapy
electron accelerators:Accelerator 4 and 6
Aarhus University Hospital, Århus Sygehus
Layout of accelerator 4
- Photons can not reach the maze door by a single scattering- Neutron door due to short maze
Aarhus University Hospital, Århus Sygehus
Accelerator 6: Layout
Photons can not reach the maze door by a single scattering
Aarhus University Hospital, Århus Sygehus
Literature• NCRP Report No. 144, Radiation Protection for Particle Accelerator
Facilities, 2003• NCRP Report No. 151, Structural Shielding Design and Evaluation for
Megavoltage X- and Gamma-Ray Radiotherapy Facilities, 2005.• Radiological Safety Aspects of the Operation of Electron Linear
Accelerators, Technical Reports Series No. 188, 1979.• Radiological Safety Aspects of the Operation of Proton Accelerators,
Technical Reports Series No. 283, 1988.• P. H. McGinley, Shielding techniques for radiation oncology facilities,
Medical Physics Publishing, 2002.• RADIATION PROTECTION AT LOW ENERGY PROTON
ACCELERATORS, Radiation Protection Dosimetry, Vol. 96, No 4, pp. 297–309 (2001).
• RADIATION PROTECTION AT HIGH ENERGY ELECTRON ACCELERATORS, Radiation Protection Dosimetry, Vol. 96, No 4, pp. 333–343 (2001)
Aarhus University Hospital, Århus Sygehus
Literature
• SHIELDING HIGH ENERGY ACCELERATORS, Radiation Protection Dosimetry, Vol. 96, No. 4, pp. 359–371 (2001).
• SPECIAL RADIATION PROTECTION ASPECTS OF MEDICAL ACCELERATORS, Radiation Protection Dosimetry, Vol. 96, No. 4, pp. 381–392 (2001).
• RADIATION PROTECTION AT MEDICAL, ACCELERATORS, Radiation Protection Dosimetry, Vol. 96, No 4, pp. 393–406 (2001).
• CALCULATIONS OF NEUTRON SHIELDING DATA FOR 10–100 MeV PROTON ACCELERATORS, Radiation Protection Dosimetry (2005), Vol.116, No. 1–4, pp. 245–251
• EVALUATION OF THE RADIOACTIVITY OF THE PRE-DOMINANT GAMMA EMITTERS IN COMPONENTS USED AT HIGH-ENERGY PROTON ACCELERATOR FACILITIES, Radiation Protection Dosimetry (2007), Vol. 123, No. 4, pp. 417–425