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ZMT 335 1 22/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak RADIOTHERAPY & NUC MEDICINE

Radiotherapy Equipment

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Page 1: Radiotherapy Equipment

ZMT 335

122/3/2017Dr. Nik Noor Ashikin Bt Nik Ab Razak

RADIOTHERAPY & NUC MEDICINE

Page 2: Radiotherapy Equipment

TOPIC 5 & 6Radiotherapy Equipment

222/3/2017Dr. Nik Noor Ashikin Bt Nik Ab Razak

Page 3: Radiotherapy Equipment

OBJECTIVE

322/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak

To understand the design and functionality of the equipment

To review physics and

technology of external beam radiotherapy equipment

Page 4: Radiotherapy Equipment

5.0 External Beam Equipment5.1 Low-energy Machines

5.1.1 Superficial Equipment5.1.2 Orthovoltage Units

5.2 Telecurie Units5.2.1 Cs-1315.2.2 Cobalt – 60 Unit

5.3 Linear accelerator (LINAC)422/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak

Page 5: Radiotherapy Equipment

5.0 External Beam Equipment

522/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak

Page 6: Radiotherapy Equipment

Therapeutic x-ray

equipment

• 10 kVp - 150 kVp (superficial);

• 150 kVp - 400 kVp (orthovoltage/ deep)

Radioactive

sources ( γ ray equipment)

• Cobalt 60 & Cesium 137

MV accelerators for X and electron

therapy

• Linear accelerator

6

5.0 External Beam Equipment

Page 7: Radiotherapy Equipment

5.1 Low-energy Machines5.1.1 Superficial Equipment5.1.2 Orthovoltage Units

722/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak

Page 8: Radiotherapy Equipment

• 10-15 kVp

• Treatment of inflammatory disorders (Langerhans’ cells), Bowen’s disease, patchystage mycosis fungoides,

herpes simplex

1.Grenz rays

• Superficial skin lesions

• Endocavitary treatments for curative

intent (rectal)

2.Contact therapy

5.1 Low-energy Machines

• Low-energy machines: Uses x-rays generated at voltages up to 500kVp

Page 9: Radiotherapy Equipment

• 50-150 kVp

• Skin cancer and tumors no deeper than 0.5 cm

3.Superficial equipment

• 150-500 kVp

• Skin, mouth, and cervical carcinoma

• Experience limitation in the treatment of lesions deeper than 2 to 3 cm.

4.Orthovoltage machines

5.1 Low-energy Machines

Page 10: Radiotherapy Equipment

“conventional” X Ray tube

with electrons accelerated by an electric field

filtration important

Stationary anode (in contrast to

diagnostic tubes which have a

rotating anode to allow for a smaller

focal spot)

Part 5, lecture 2: Equipment - superficial, telecurie

10

5.1 Superficial / Orthovoltage equipment5.1 Low-energy Machines

Page 11: Radiotherapy Equipment

5.1 Superficial / Orthovoltage equipment

Can not reach deep-seated

tumors with an adequate dosage

of radiation

Do not spare skin and

normal tissues.

LIMITATIONS OF

LOW ENERGY MACHINES

5.1 Low-energy Machines

Page 12: Radiotherapy Equipment

Part 5, lecture 2: Equipment - superficial, telecurie 12

5.1 Superficial / Orthovoltage equipment

50 to 150kVp

small skin lesions

maximum applicator size typically < 7cm

typical FSD < 30cm

beam quality measured in HVL aluminium (0.5 to 8mm)

Superficial

150 to 500kVp

applicators or diaphragm

skin lesions, bone metastases

FSD 30 to 60cm

beam quality in HVL copper (0.2 to 5mm)

Orthovoltage

5.1 Low-energy Machines

Page 13: Radiotherapy Equipment

5.1.1 Superficial Equipment

1322/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak

Page 14: Radiotherapy Equipment

Part 5, lecture 2: Equipment - superficial, telecurie

14

Superficial X Ray tube (Philips RT 100)

• Manufacturers picture...

X Ray tube

Cooling

water Target

Applicator/

collimator

5.1.1 Superficial Equipment5.1.1 Superficial Equipment

Page 15: Radiotherapy Equipment

Part 5, lecture 2: Equipment - superficial, telecurie

15

X-ray tube

ApplicatorFilter

5.1.1 Superficial Equipment

Page 16: Radiotherapy Equipment

X-ray produced at

50-150 kV

Varying thickness of filtration

(usually 1-6 mm Al) are added to

harden the beam to

a desire degree

Superficial treatment are usually given

with the help of applicators or

cones attachable to the diaphragm

of the machine

SSD range 15 to 20 cm

5.1.1 Superficial Equipment

Page 17: Radiotherapy Equipment

17

Superficial x-ray equipment (cont)

• Dose is highly dependent on source-skin distance, filtration and

applicator area.

5.1.1 Superficial Equipment

15 cm FSD cones

25cm FSD cones

Page 18: Radiotherapy Equipment

5.1.1 Superficial Equipment5.1.1 Superficial Equipment

Usually operated

at 5-8 mA

Beyond this depth, the dose drop-off is too

severe to deliver adequate depth dose without considerable

overdosing of the skin

surface

Useful for irradiating

tumor confined to about 5 mm depth (~90%

depth dose)

Page 19: Radiotherapy Equipment

5.1.1 Superficial Equipment

• Short focus to skin distance (FSD) and hence high output and large

influence of inverse square law

• Calibration difficult due to strong dose gradient i.e. dose fall off and

electron contamination

Issues with Superficial

radiotherapy

Page 20: Radiotherapy Equipment

5.1.2 Orthovoltage Units

2022/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak

Page 21: Radiotherapy Equipment

Uses conventional

X-ray tube

Energy range 150-

500 kV X-rays

Mostly used around

250 - 300 kVp

Applicators are used

in superficial therapy

Treatment depths of

around 20 mm

Penetration sufficient for palliative treatment of bone

lesions relatively close to the surface (ribs, spinal cord)

5.1.2 Orthovoltage Units5.1.2 Orthovoltage Units

Page 22: Radiotherapy Equipment

5.1.2 Orthovoltage Units5.1.2 Orthovoltage Units

• Higher dose to bone - photoelectric

absorption

• Maximum dose on the surface

hence higher skin dose

• Treatment to a depth of only a few

centimeters possible

• Low energy, hence high scattered

radiation and larger penumbra

Disadvantages Of Deep X-ray

Page 23: Radiotherapy Equipment

5.2 Telecurie Units5.2.1 Cs-1315.2.2 Cobalt – 60 Unit

2322/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak

Page 24: Radiotherapy Equipment

Part 5, lecture 2: Equipment - superficial, telecurie 24

5.2 Telecurie Units

Features of a

Teletherapy

Source

high energy gamma ray emission high

specific air kerma rate constant

simple means of

production

Low cost

high specific activity

long half-life

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Part 5, lecture 2: Equipment - superficial, telecurie 25

5.2.1 137-Cs

137-Cs

Photon energy 0.66MeV

Relatively large source to relatively low specific activity

Medium FSD (around 60cm)

No isocentric mounting - similar to orthovoltage equipment in set-up

Not sold anymore and should not be in use

Page 26: Radiotherapy Equipment

5.2.2 Cobalt – 60 Unit5.2.2.1 Properties5.2.2.2 Application5.2.2.3 Production 5.2.2.4 Source5.2.2.5 Activity5.2.2.6 Half-Life5.2.2.7 Shielding5.2.2.8 Penumbra5.2.2.9 Dose Maximum5.2.2.10 Equipment5.2.2.10 Cobalt – 60 Equipment5.2.2.11 Annual dose to staff5.2.2.12 Gamma Knife 2622/3/2017 Dr. Nik Noor Ashikin Bt Nik Ab Razak

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Part VII.14.3 : Radiation Sources in Teletherapy Slide 28

Natural Cobalt (59Co)COBALT - Kobald, from the German for goblin or evil spirit. Discovered in 1735. Brittle hard metal similar

to iron and nickel. Found in minerals and meteorites. Salts and glass oxides are deep blue in colour.

5.2.2 Cobalt – 60 Unit

Page 29: Radiotherapy Equipment

5.2.2 Cobalt – 60 Unit

ORTHOVOLTAGE UNIT

150-500 KV x-rays

Maximum dose on the skin

Treatment to a depth of few centimeters

Higher absorption by bone

non uniform dose distribution

Higher side scatter hence larger penumbra

Telecobalt Unit

1.25 MeV ال Photon

Maximum dose at depth of 5 mm

Relatively uniform dose absorption

Higher penetration deep seated tumours

Relatively uniform distribution

More of forward scatter, lesser penumbra

Mostly isocentric unit

5.2.2 Cobalt – 60 Unit

Page 30: Radiotherapy Equipment

5.2.2 Cobalt – 60 Unit

Linear Accelerator

4 to 21 MV photon beams

Maximum dose at higher depth with energy

No radioactive source

Radiation only when the source is switched is ON

Uniform dose absorption

1mm source – nearly point source

Small Penumbra

Electron beam of various energies possible

Telecobalt Unit

1.25 MeV ال Photon

Maximum dose at depth of 5 mm

Source to be changed every 4 to 5 yearsLeakage radiation present even while the beam is

off

Relatively uniform distribution

1-2 cm source diameter

Larger penumbra

Gamma Photon only

5.2.2 Cobalt – 60 Unit

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Introduced in the 1950’s, being replaced

by linacs.

The first practical radiation therapy treatment unit to

provide a significant dose below the skin

surface and simultaneously spare

the skin the harsh effects of earlier

methods.

Still used in developing countries: simpler

design, cost, little tech support.

5.2.2 Cobalt – 60 Unit

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Photon energy around 1.25MeV

Specific activity large enough for FSD of 80cm or

even 100cm

Therefore, isocentric set-up

possible

Constantly emit radiation

60Co source must be shielded in a

protective housing (source head).

source head is a steel shell filled

with lead (may be up to 2 ft in

diameter

PROPERTIES

5.2.2.1 Properties

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5.2.2 Cobalt – 60 Unit5.2.2.2 Application

AP

PL

ICA

TIO

N

To treat cancers of the head and neck area, breast, spine, and

extremities

Areas just below the skin surface

Ideal in treating lymph nodes.

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5.2.2 Cobalt – 60 Unit5.2.2.3 Production of Cobalt – 60

1

• Cobalt: produced in nuclear reactors by the irradiation of neutrons of the common stable form of 59Co.

2

• The 59Co nucleus absorbs a neutron in the reactor and becomes 60Co.

3

• Radioactive 60Co produces a useful therapy beam when it undergoes beta decay

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5.2.2 Cobalt – 60 Unit5.2.2.3 Production of Cobalt – 60

4

• The nucleus emits a beta particle and then two photons, 1.17 MeV and 1.33 MeV for an effective energy of 1.25 MeV

5• 60Co 60Ni+ + B- + neutrino (v) + gamma rays

6

• Radioactive 60Co emits radiation in the form of high energy gamma rays in an effort to return to its more stable state.

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5.2.2 Cobalt – 60 Unit5.2.2.4 Cobalt – 60 Source

Of the close to 300 natural nuclides and over 3000 artificially produced radionuclides, only four meet the teletherapy source requirements (Co-60, Cs-137,

Eu-152, and Ra-226) and only cobalt-60 is actually used in practice.

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5.2.2 Cobalt – 60 Unit5.2.2.4 Cobalt – 60 Source

• 1 to 3 centimetersDiameter of a 60Co source

• Encased in multiple layers of welded metal to prevent

contamination of the environment and to absorb β-particles produced by the decay process.

Source Form: Pellets of radioactive 60Co

• Smaller source with less penumbra for the same beam intensity

• Less hazard of contamination should a source ever become exposed to the environment.

Source Form: 60Co fused into a solid cylinder

Page 38: Radiotherapy Equipment

Part VII.14.3 : Radiation Sources in Teletherapy Slide 38

How does a teletherapy Cobalt source look?

3500 pellets; 275 Ci/g; 7700 Ci

5.2.2.4 Cobalt – 60 Source

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Part VII.14.3 : Radiation Sources in Teletherapy Slide 39

Cobalt source – how does it look?5.2.2.4 Cobalt – 60 Source

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5.2.2 Cobalt – 60 Unit5.2.2.5 Cobalt – 60 Activity

SI unit: Curies (Ci)3.7 x 1010 Becquerel

(Bq)

1 Bq = 1 disintegration

per second

also defined in rhm units (roentgens per hour at 1

meter)

Most sources have an activity of 750-9000 Ci, typically 3000-9000 Ci

used in radiation therapy

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•Half-life: the time necessary for a radioactive material to decay to half or 50% of its original intensity.• Requires a correction factor for this decay of about 1% per month in all

treatment calculations.

• Source must be replaced at about five year intervals.

• The half-life of 60Co is 5.26 years.

5.2.2 Cobalt – 60 Unit5.2.2.6 Cobalt – 60 Half-Life

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5.2.2 Cobalt – 60 Unit5.2.2.7 Cobalt – 60 Shielding

Cerrobend (Lipowitz metal):

Lower melting point than Pb, cheaper

50% Bismuth

26.7% Lead

13.3% tin

10% Cadmium (a toxic metal can get

into bloodstream

Density ratio of Cerrobend to Lead:

1.2 cm Cerrobend to 1 cm lead.

5 HVL is needed to reduce intensity

A thickness of 7.2 cm of

Cerrobend needed, 6 cm lead.

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• Penumbra: the area at the edge of the radiation beam at which the dose rate changes rapidly as a function of distance from the beam axis.5.2.2 Cobalt – 60 Unit5.2.2.8 Penumbra

1• Describes the edge of the field having full radiation intensity for the

beam compared with the area at which the intensity falls to 0.

2• The larger the source size, the larger the penumbra

3• Larger field sizes are necessary to cover the same amount of tissue

adequately compared to the linac.

4

• Geometric penumbra typically wide because source diameter is large (>2cm)

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Part 5, lecture 2: Equipment - superficial, telecurie 48

5.2.2 Cobalt – 60 Unit5.2.2.8 Penumbra

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5.2.2 Cobalt – 60 Unit5.2.2.8 Penumbra

The transmission penumbra can be reduced by using

satellite collimators,

penumbra trimmers

or trimmer bars

Trimmers are metal bars that attenuate the edge of the

beam providing a sharper field

edge.

It Should be placed no closer

than 15 cm from the

patients skin to reduced electron

contamination (increased skin dose) by metal

devices.

Provides enough distance

for the secondary electrons

produced by the trimmer bars to lose sufficient

energy

REDUCING PENUMBRA

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5.2.2 Cobalt – 60 Unit5.2.2.9 Dose Maximum

Dose maximum (Dmax): when a

greater percentage of dose occurs below the skin

surface

Dmax is the depth of maximum

buildup, in which 100% of the dose

is deposited

For 60Co, Dmax

occurs at 0.5 cm below the skin

surface.

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Part 5, lecture 2: Equipment - superficial, telecurie

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• Source head and transfer mechanism

5.2.2.10 Cobalt – 60 Equipment

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Part 5, lecture 2: Equipment - superficial, telecurie

54

5.2.2.10 Cobalt – 60 Equipment

• shield against the primary cobalt-60

beam

Primary barriers

• shield against leakage radiation and radiation scattered

from the patient

Secondary barriers

Typical cobalt-60 teletherapy installation:

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11. Beam On/Beam Off

5.2.2 Cobalt – 60 Unit5.2.2.10 Cobalt – 60 Equipment

• Turning the beam on requires physically exposing the source either by moving it into position or by removing shields around the source.

Turning the beam

• the compressor generates air pressure by pushing the source horizontally into position over the collimator opening.

Air pressure:

• the motor rotates a wheel 180 degrees by placing the source over the collimator opening.

Rotating wheel:

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5.2.2.10 Cobalt – 60 Equipment

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Part 5, lecture 2: Equipment - superficial, telecurie

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Picture of a Co source change

5.2.2.10 Cobalt – 60 Equipment

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Part 5, lecture 2: Equipment - superficial, telecurie

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•Assume:• 200 days, 8hours per day working time per year

• 10% of this time in treatment room

• 3 Gy h-1 typical dose averaged over all locations of the staff member in the treatment room

•Dose = 200 x 8 x 0.1 x 3 Gy

• 0.5mGy/year (half of dose limit for general public)

5.2.2 Cobalt – 60 Unit5.2.2.11 Annual dose to staff

Page 59: Radiotherapy Equipment

5.2.2 Cobalt – 60 Unit5.2.2.12 GAMMA KNIFE

Therefore it is also known as the stereotactic surgery

Patient wears a specialized helmet that is surgically fixed to their skull (brain tumor remains stationary at target point of the gamma rays)

It is placed in a circular array in a heavily shielded assembly

Aims gamma radiation through a target point in the patient's brain.

Contains 201 cobalt-60 sources of approximately 30 curies each

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Patient positioning collimator

5.2.2 Cobalt – 60 Unit5.2.2.12 GAMMA KNIFE

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5.2.2.12 GAMMA KNIFE