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Medical Linear Accelerators in Radiation Therapy: Haijun Song, PH.D

Medical linear accelerators (linacs) are commonly used in radiation therapy to treat cancer. A linac produces high energy x-ray beams through linear particle acceleration. It contains components such as a beam collimator, multi-leaf collimator, and cone that shape the beam to precisely target the tumor. Advanced techniques like intensity modulated radiation therapy (IMRT) further sculpt the dose distribution to conform to the tumor while sparing surrounding healthy tissue. Image guidance during treatment ensures accurate beam delivery to the target. Radiation oncology can offer small animal researchers many state-of-the-art radiation delivery techniques to advance radiobiology research.

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70 views43 pages

Medical Linear Accelerators in Radiation Therapy: Haijun Song, PH.D

Medical linear accelerators (linacs) are commonly used in radiation therapy to treat cancer. A linac produces high energy x-ray beams through linear particle acceleration. It contains components such as a beam collimator, multi-leaf collimator, and cone that shape the beam to precisely target the tumor. Advanced techniques like intensity modulated radiation therapy (IMRT) further sculpt the dose distribution to conform to the tumor while sparing surrounding healthy tissue. Image guidance during treatment ensures accurate beam delivery to the target. Radiation oncology can offer small animal researchers many state-of-the-art radiation delivery techniques to advance radiobiology research.

Uploaded by

Harley Alejo M
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Medical Linear Accelerators

in Radiation Therapy

Haijun Song, Ph.D.

Dept. of Radiation Oncology


Duke University Medical Center
MV Linear Accelerator
Anatomy of a Linac
Anatomy of a Linac
Beam Mofiers
Cone

MLC (Multi-Leaf Collimator)


Radiosurgery with Linac
MLC
Conformal RT (3DCRT) &
Intensity Modulation RT (IMRT)
Conformal RT (3DCRT) &
Intensity Modulation RT (IMRT)
Dose Map delivered by IMRT
Dose Map delivered by IMRT
Dose Map delivered by IMRT
Image Guided RT (IGRT)
Respiratory Gating RT
Tomotherapy and Robotic
Difference among
Radiation Sources
Factors affecting radio-bio response
• Gamma vs. Electron

Among Gamma sources


• Photon Energy Spectrum
• Dose Distribution
• Dose Rate
Radioactive Isotopes
Example: Cs-137
• single dominant energy, 0.66 MeV
• Activity: 6000 Ci and 100 Ci, dual source
• Dose rate range: 0.001 - 10 Gy/min
Radioactive Isotopes
Example: Ir-192
• Complex energy spectrum: 30 gammas and
40 x rays.
• Dose rate, 0.01 - 5 Gy/min being used RT.
Ir-192 photon spectrum

1000

100
Percent per decay

10

0.1

0.01

0.001
0.001 0.01 0.1 1 10
0.0001
E (MeV)
From kV to MV
Commonly: 50 – 300 kVP
Beam Quality: HVL a few mm Al to Cu.
Dose Rate: around Gy/min
From kV to MV
Commonly: 6 MV -25 MV
Beam quality: PDD10 in water, 67% and up.
Dose Rate: around Gy/min
X-Ray tube vs. Linac
Acce. Tube: Travelling Wave
X-Ray Production
Side emission vs. straight through emmission
Photon energy spectrum
from a 6 MV beam
Fl uence/ MeV/ I ndiFlcent el ect
uence/ MeV/r on
I ndi cent
el ect r on
1. 40E- 04

1. 20E- 04

1. 00E- 04

8. 00E- 05

6. 00E- 05

4. 00E- 05

2. 00E- 05

0. 00E+00
0 1 2 3 4 5 6
Depth Dose Curves
Dose Distribution:
One beam/parallel beams
Dose Distribution:
One beam/parallel beams
MV photon and electron beams
Depth Dose of e Beams

100

90

80
Percent Depth Ionization

70

60
6 8 10 12 15 18 M eV
50

40

30

20

10

0
0 1 2 3 4 5 6 7 8 9
D e p th ( c m ) in W a te r
Dose Measurement
DwQ = M * kQ N D60,wCo
Ion chamber and electrometer
In water for MV photon or electron beams
In air for KV beams
Tracable to NIST Co-60 standard beam
Buildup region and skin sparing
Compton e1 1 1 1

Compton e2 1 1 1

Compton e3 1 1

Compton e4 1

Depth in water Æ

Total dose 1 2 3 3
Treating Superficial targets
Bolus: tissue equivalent, soft to conform to skin

100
B dmax

80
Percent Depth Dose

60

S
40

20

0
0 1 2 3 4
Depth in Water (cm)
Dose Distribution:
One beam/parallel beams
Buildup region and skin sparing
continued
Skin sparing also means a target at shallow depth
will not get adequate dose.

For small animals, “sparing” of a couple of


centimeter from skin may “spare” the whole animal.

What do we do when we need to treat superficial


target?
Bolus
Treating Superficial targets
Bolus: tissue equivalent, soft to conform to skin

100
B dmax

80
Percent Depth Dose

60

S
40

20

0
0 1 2 3 4
Depth in Water (cm)

bolus
Treating Superficial targets
Bolus: tissue equivalent, soft to conform to skin

100
B dmax

80
Percent Depth Dose

60

S
40

20

0
0 1 2 3 4
Depth in Water (cm)

bolus
Treating Superficial targets

MeV range electron beams /w bolus

kV (suferfical units, orthovoltage units)

MV photon beam with bolus

How useful are MeV electron beams for


small animal irradiations?
What can Rad Onc
Offer Rad Biology
All offered to human can be offered to other species.

Imaging: CT, MRI

Precise and conformal dose coverage: 3DCRT, IMRT, IGRT,


Respiratory Gating, radiosurgery, electron irradiation.

Precision and conformality means sparing healthy tissue, too.

And More: Brachytherapy, hyperthermia, proton, neutron.


Acce. Tube: Standing Wave
Acce. Tube: Short Standing Wave

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