PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15
Radiotherapy Treatment
Machines for Cancer
PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15
A. Purpose
1. Selective irradiation of the 3D
volume of a malignant cancer
is the goal of radiation therapy.
B. Basic process
1. Deliver a sufficiently fatal
dose of radiation to the target
volume while minimizing the
damage to surrounding normal
tissue.
Radiotherapy Treatment Machines for Cancer
PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15
After This Presentation You Will Know…
I. Spatially varying the intensity of an x-ray beam
II. IMRT
III. Planning
IV. Beam generation
V. Beam modification
VI. Dose measurement
VII. Treatment delivery
VIII. Results
PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15
Spatially Varying the Intensity of an X-ray Beam
A. Problem: Smart Tumor growth issue
1. Tumors typically entangle themselves around and near
delicate tissues and grow into complex three-dimensional
shapes so it is difficult to minimize the damage to the
surrounding tissues while still administering a tumorcidal
dose.
B. Solution: Intensity-modulated radiation therapy (IMRT)
1. Method of external beam radiation therapy that modulates
the dose to conform to the size, shape, and location of the
tumor.
PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15
IMRT• Intensity Modulated Radio Therapy (IMRT)
• External-beam radiotherapy • Planning
• 4D-CT • Dose calculations are performed with treatment planning software
• Analytical algorithm, AAA • IMRT is administered using the Linear accelerator (LINAC) which employs 4
main processes:
1.Beam generation
2.Beam Modification
3.Dose Measurement
4.LINAC control
PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15
IMRT vs. VMAT
IMRT(L) & VMAT(R)
• Plan geometries [(a), (d)]
• Dose distributions in axial views [(b), (e)]
• Films in sagittal views [(c), (f)].
PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15
How to Plan Dose DistributionI. Analytical algorithms
are used in calculating
dose distribution in the
planning stage
A. AAA- Anisotropic
analytical algorithm
(AAA) 10.0.24. 1. Absolute point dose
a) Measured with
thermoluminescent
dosimeters(TLDs)
2. Planar dose
a) GafChromic® EBT2 film
Dose distributions in an axial view
PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15
Beam Generation: The LINAC
• The electrons are produced by the electron gun by thermionic emission from heated cathode to produce a beam that accelerates toward the anode.
• The electrostatic field between focuses the beam prior to entering the wave guide
• Steering coils control inlet direction
• Deflects charged electrons perpendicular to magnetic field
• Once inside the accelerator wave guide the electromagnetic field of the radio frequency waves transfer energy to the electrons
• Grouping the electrons
• Traveling wave
PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15
Beam Modification• Focusing coils & outlet
steering coils to ensure correct direction and continual focus of the beam
• Achromatic bending system • Further modification occurs in
the treatment head, high energy electrons converted to photons or x-rays
• Multileaf collimator modifies beam to ensure the shape of the delivered beam matches that of the tumor
PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15
Dose Measurement• Photons pass through ion chamber for
dose measuring and beam quality monitoring.
• Dose measured and controlled simultaneously
• 2 independent ionization chambers: 1. The primary dosimeter. 2. secondary Ion-chamber.
• Dose measurement and administration are done simultaneously.
• Further shaping of the beam with multi-leaf collimator
PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15
Dose Measurement continued• Each part of the human body presents its own challenges
that require solutions in order for the treatment to be
plausible and provide necessary treatment with the
minimal damage to the healthy surrounding tissues. • IMRT treatments in the body cavity
• Gate the x-ray beam in synchrony with the
movements due to breathing • Complicated by the inevitable anatomical
and medical variances in human patients • In the head and pelvis
• How much damage to spare a section, possibly a
gland, while also delivering a sufficient amount.
PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15
Treatment Delivery• LINAC control
• One computer system controls both
LINAC and the multi-leaf
collimator. • Allows for synchrony between
delivery dose and multi-leaf
collimator. • Direct effects due to delivery
• Tumorcidal dose delivered and minimal
exposure to surrounding tissues • often patients experience epidermal
scars
PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15
The image below is a Varian’s Clinac Linear Accelerator. It generates high
doses of radiation to kill cancer cells. With SmartBeam IMRT, that
allows more tightly focused delivery beams to the cancerous tumors.
Results • IMRT radiotherapy machines…..
• Reasonably fast computation time • Effective delivery • Minimizes damage to surrounding sensitive tissues • Very successful form of treatment for cancers especially with
the tumors that have a more difficult conformation complicated
by sensitive surrounding tissues. • Accuracy of measurement and delivery is constantly being
improved upon.
PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15
Conclusion• We discussed…
• Spatially varying the intensity of an x-ray beam
• IMRT planning using AAA
• The critical importance of the Linear Accelerator in IMRT treatments
• Beam generation
• Beam modification
• Dose measurement
• Treatment delivery
• Results
PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15
ReferencesI. Barnett GC, Wilkinson J, Moody AM, et al. A randomized controlled trial of forward-planned
radiotherapy (IMRT) for early breast cancer: baseline characteristics and dosimetry results.
Radiotherapy and Oncology. 2009;92:34–41.
II. Boyer, Arthur L. "The physics of intensity-modulated radiation therapy." Physics Today 55.9 (2002):
38-43.
III. Christian JA, Bedford JL, Webb S, et al. Comparison of inverse-planned three- dimensional
conformal radiotherapy and intensity-modulated radiotherapy for non-small-cell lung cancer. Int J
Radiat Oncol Biol Phys. 2007;67:735–41.
IV. Constantin, Dragoş, Rebecca Fahrig, and Paul Keall. "A Study of the Effect of In-line and
Perpendicular Magnetic Fields on Beam Characteristics of Electron Guns in Medical Linear
Accelerators." Medical Physics. American Association of Physicists in Medicine. Web. 23 Nov. 2015.
V. Han, Tao, Firas Mourtada, Kelly Kisling, Justin Mikell, David Followill, and Rebecca Howell.
"Experimental Validation of Deterministic Acuros XB Algorithm for IMRT and VMAT Dose
Calculations with the Radiological Physics Center’s Head and Neck Phantom." Medical Physics.
American Association of Physicists in Medicine. Web. 17 Nov. 2015.
VI."Intensity Modulated Radiotherapy (IMRT)." Intensity Modulated Radiotherapy (IMRT). Web. 23
Nov. 2015. <http://www.cancerresearchuk.org/about-cancer/cancers-in-general/treatment/
radiotherapy/external/intensity-modulated-radiotherapy-imrt>.
PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15
The End
PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15
Top Related