AL307 MODULE 1: TREATMENT DELIVERY EQUIPMENT

John M. Kratina, BMEd, RT(R )(T) LRT - Instructor Copyright 2009 John M. Kratina

Tx Delivery Equipment

Washington Chapter 7

Before 1950 - Kilovoltage units - grenz, contact, superficial & orthovoltage - external beam radiation therapy - voltages up to 300 kVp

  50-120 kVp - superficial machines - soft, nonpenetrating x-rays,

maximum dose is on the surface - treats superficial lesions.  150-500 - orthovoltage units - maximum dose occurs at or very close

to the skin surface.  Early 1950's - 60CO machines, high energy betatrons  1951 - 60CO - Canada  1956 linear accelerators

Kilovoltage Equipment

  Grenz-rays - Bucky rays, low energy x-rays

having an energy of 10-15 kVp.  Grenz rays are almost entirely absorbed in

the first 2 mm of skin - has a useful depth dose of about 0.5 mm

  Used to treat inflammatory disorders,

Bowen's disease, patchy stage mycosis fungoides and herpes simplex

Contact Therapy

Was used to treat superficial skin lesions.  Machine actually came in contact with

the patient.  Also was used to treat rectal cancers

confined to the bowel wall.  Used low energy x-rays.

Superficial Therapy

50-150 kV uses 1-6 mm thick al filters hardens the beam

  Uses cones or applicators from 2-5 cm in diameter  Lead cutouts are tailored to fit the treatment area.  Cone lies directly on the skin or lead cutout SSD 15-20

cm.  Skin cancer & tumors no deeper than 0.5 cm are

treated

Orthovoltage therapy

150-500 kV most machines 200-300 kV and 10-20 mA.

  Use filters - SSD 50 cm - cones  Treat tumors of skin, mouth, cervical

carcinoma (cones inserted into patient)  Squamous cell & basal cell cancers 2-3 cm

Megavoltage Equipment

  1 mV or greater  Van de Graaff generator, linear

accelerator, betatron, cyclotron, 60CO

Betatron

1941 - x-rays of 2 mv- 40 mv  Were used during WWII to x-ray castings and other metal sections of

equipment.  Operation of the betatron - An electron in a changing magnetic field

experiences acceleration in a circular orbit.  Used with superficial tumors or gynecological, bladder and prostate

carcinomas.  Very large machines requiring large treatment rooms - have limited

motions, compromising beam direction and flexibility of patient set-ups.

  Machine was noisy, therapists would put cotton balls & mufflers over

patients ears to reduce noise.

Van de Graaff generator

 1937 - 2 mV, 100 SSD  Linear type of electrostatic accelerator.  Treated seminoma, whole brain & mantle field  Warm-up could be lengthy - up to 1 hour  Very bulky machine - therapists had to measure the

distance to the patient with a front-pointer device.  Patient had to be on a stretcher

Proton Accelerator

Cyclotron - 1928 - charged particle accelerator used for nuclear research  Accelerates protons, neutron beams, light ions, and heavy charged

particles used in radiation therapy.  Produces radionuclides used in position emission tomography (PET)  Used in nuclear medicine studies to measure physiological & biomedical

processes. e.g., blood flow, oxygen, glucose, & metabolism of free fatty acids, amino acid transport, pH, and neuroreceptor densities.

  PET used in research centers.  PET uses radiation emitted from within the patient to produce images.  Cyclotrons are expensive to install ($1 million) and operate.

Fast Neutrons (cyclotron)

Fast Neutrons (cyclotron) - used in radiation therapy to treat glioblastoma multi forme (brain). Squamous cell of head & neck, salivary gland tumors, lung cancer, prostate tumors, soft tissue carcinomas.

  They are not used as much as protons because of their inferior depth

doses.  Proton (cyclotron) effective in treating benign & malignant lesions

(pituitary gland)  Single high dose to a small precise area.  Ocular melanoma, soft tissue and bone sarcomas, prostate, head &

neck  New proton accelerator being planned in Boston in 1998.

Advantages of Protons

1.precision controlled 2. scattering is minimal 3. have a characteristic

distribution of dose with depth 4.most of the energy is deposited

near the end of their range, where the dose peaks to a high value & then drops rapidly to zero (Bragg Peak)

Remote afterloading

  Low or high dose remote afterloading with the use of

brachytherapy isotopes  An active radioisotope was preloaded in an applicator

before being placed in the patient. Radium was the isotope commonly used. Half life of 1620 years.

1950's afterloading applicators were developed.  Dummy sources were placed in the patient then

radiographed for placement.  Cesium 137 was being used - half life of 30 years.

Low dose rate - disadvantages  sources can shift in the body

patient is in the hospital - usually several days

can make treatment plan changes if needed

High dose rate - advantages 1.Treatment can be given on an outpatient basis 2.Treatment time is extremely short 3.Because of short treatment time the implant

reproducibility is more precise than with manual systems

4.Complete radiation protection for staff members

5.No general anesthesia or bed rest - decreases complications

6.system can treat a large patient volume 7.Source optimization 8.Increased level of comfort for the patient

With LDR & HDR Optimum tumor dose distribution can

be achieved while normal tissue exposure is minimized.

  HDR - treatment plan changes are

difficult to make because of the short length of time for treatment.

Linear Accelerator

Linear Accelerator - charged particles travel in straight lines as they gain energy from an alternating electromagnetic field.

  Cyclotron - particles travel in a spiral

pattern  Betatron - particles travel in a

circular pattern

History

1961 - 1st 100 cm, SAD, fully isocentric linear accelerator - Varian - manufactured in U.S.

  Cobalt 60 was the most common

treatment unit in the 70's and 80's

Advantages of linear accelerators over Cobalt 60Higher beams: Greater skin sparing Field edges are sharper Personnel receive less radiation

leakage

Cobalt 60

For COBALT 60, ALL YOU NEED TO KNOW IS:* THE HALF-LIFE (t1/2) IS 5.26 YEARS. *CO60 AVERAGE ENERGY IS 1.25 MEV.

*IT’S BEAM HAS LOT MORE PENUMBRA THAN A LINAC BEAM, BECAUSE THE CO60 SOURCE IS MUCH LARGER.

*A "T-BAR" IS USED TO RETRACT A STUCK CO60 SOURCE.

THE RADIATION SAFETY OFFICER DOES THIS. NOT THE RTT.

*It is now being used in the GAMMA KNIFE.

LinAc History

1930:William Hansen - instructor at Stanford University - California - working on research in atomic physics

  David Sloan - working on the cyclotron at Berkeley  Klystron - a form of radiowave amplifier & multiplies

the amount of introduced radiowaves greatly.  The British group of D.D. Fry at Telecommunication

Research Establishment in Great Malvern, England, was inventing the magnetron - a device similar to the klystron

LinAc History

Difference -   Klystron is a linear beam microwave

amplifier requiring an external oscillator or radiofrequency (RF) source driver

  Magnetron - is an oscillator &

amplifier

LinAc History

1948:A working 1 MV linear accelerator was installed at the Ferm's Institute in Chicago

  The mile-long waveguide, which ran under University Blvd at the

University of Chicago provided photon and electron beams.  June 1952 - 1st linear accelerator was installed at Hammersmith

Hospital in London.   1st treatment - August 1953 - 8 MV photon beam  1953 - 4 MV linear accelerator Newcastle General Hospital

1954 - Christie Hospital, Manchester England  By lowering part of the floor - the first single gantry unit could be

rotated over an arc of 120o

LinAc History

6 MV Ergonomic linear accelerator was produced between British industrial work and Stanford University.

  Could rotate 360o around a patient.  Ergonomics - is the science of attempting to adapt a

situation with the least exertion of energy by the operator of the equipment

  1994 - Total of 2733 megavoltage treatment units

increased 17% 1990  2418 linear accelerators or betatrons

315 cobalt units

Three types of Linear Accelerators1.early linear accelerators 1953 – 1961

2.second generation 360o rotational units 1962-1982

3.new computer driven, third generation treatment machines

LinAc History

Early accelerators - big & bulkyfirst installed 8 MeV x-ray beamlimited gantry motion

  Second generation - the older 360 degree

rotational units- isocentric units- some are still in use built between 1962-1982- usually require alot of maintenance

Third generation accelerators

have improved accelerator guide, magnet systems beam modifying systems to provide a wide range of beam energy dose rate, field size & operating modes

  With improved beam characteristics

they are highly reliable have compact design features computer driven dual photon energies multi leaf collimation several electron energieselectronic portal verification system

Third generation acceleratorsA linear accelerator produces a high

energy x-ray or electron beam. In the Tx Room, there are Three major

components of a linear accelerator:1. drive stand2. gantry3. treatment couch

Third generation accelerators: Treatment Room A treatment room is designed with thick concrete walls or lead walls for

shielding.  The gantry is mounted to the stand, stand is secured to the floor.  Gantry can rotate 360o

  Treatment couch is mounted on a rotational axis around the isocenter.

Permits the positioning of a patient lying supine or prone.  Lasers - one ceiling & 2 side lasers project small dots or lines on the

patients.  Midsagittal laser - continuous line along the sagittal axis of the patient.  One or more closed circuit TV cameras are in the treatment room to

monitor the patient during treatment.

THE MAIN COMPONENTS THAT YOU WILL BE EXPLORING ON YOUR LINAC LAB ASSIGNMENT: 1-KLYSTRON 2-WAVEGUIDE 3-CIRCULATOR 4-H20 COOLING SYS 5-e- GUN 6- ACCEL. STRUCTURE 7-BENDING MAGNENT8-FLATTENING FILTER9-SCATTERING FOIL10-ADDITIONAL ACCESSORIES, CONES,

References

Washington and Leaver text, “The Principles and Practice of Radiation Therapy. (used with permission.)

Stanton and Stinson text, “Radiation Oncology Physics.” (used with permission.)

All images used with permission. My Lecture Notes

LinAc Lab Assignment

Please see the LinAc Lab Assignment in the Module 1 Folder (Lessons Page) for all the Details. The Deadline for submitting this via the Assignment Dropbox is November 4, 2009.

Quiz 1

Quiz 1 is over Chapter 7 -Washington & Leaver, Chapter 9 -Stanton & Stinson and my lecture notes.

Quiz 1 will be on-line at 2:30pm Central Time on Monday, August 31st.

What’s next?

For Monday, September 14th: Please read Treatment Procedures, Chapter

8, Washington Text and my lecture notes. Please be prepared to discuss this material at our meeting.

Quiz 2 over Chapter 8 will be on-line at 2:30pm Central on 9/14/09 .

You will be given a 7 day window to complete the quiz. 

Have a good week!

Please send me an e-mail or call me if you have any questions.

Copyright 2009 John M. Kratina