AL307 Module 1 Treatment Delivery Equipment John M Kratina BMEd RTR T LRT Instructor Copyright 2009 John M Kratina Tx Delivery Equipment Washington Chapter 7 Before 1950 Kilovoltage ID: 768466
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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 - 60 CO machines, high energy betatrons 1951 - 60 CO - 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, 60 CO
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 60 Higher 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 120 o
LinAc History 6 MV Ergonomic linear accelerator was produced between British industrial work and Stanford University. Could rotate 360 o 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 Accelerators 1.early linear accelerators 1953 – 1961 2.second generation 360 o rotational units 1962-1982 3.new computer driven, third generation treatment machines
LinAc History Early accelerators - big & bulky first installed 8 MeV x-ray beam limited 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 energies electronic portal verification system
Third generation accelerators A 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 stand 2. gantry 3. 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 360 o 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 MAGNENT 8-FLATTENING FILTER 9-SCATTERING FOIL 10-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 31 st .
What’s next? For Monday, September 14 th : 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