radiotherapy treatment machines for cancer · radiotherapy treatment machines for cancer ... i....

PHYS 3305 - Modern Physics Tia Szczesniak 12/3/15

Radiotherapy Treatment

Machines for Cancer


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


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


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.


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


IMRT vs. VMAT

IMRT(L) & VMAT(R)

• Plan geometries [(a), (d)]

• Dose distributions in axial views [(b), (e)]

• Films in sagittal views [(c), (f)].


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


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


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


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


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.


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


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.


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


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>.


http://www.cancerresearchuk.org/about-cancer/cancers-in-general/treatment/radiotherapy/external/intensity-modulated-radiotherapy-imrt

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