Machines with a Target
X-rays are produced when
high speed electrons collide with a heavy metallic target (high atomic number)
Conventional low-energy equipment
• Typically use x-rays generated at voltages as high as 300-kV(p) (kilovoltage peak)
• have been used in radiation therapy since the turn of the twentieth century.
• These kilovoltage units (low x-ray voltage radiation therapy treatment machines) include:
--Grenz --Contact --Superficial --Orthovoltage machines
hence the name Superficial Therapy.
• Commonly used to treat lesions close to or on the skin surface
Orthovoltage therapy machines operate in the
150 – 500 kv range.
To protect radiation therapists from radiation exposure
the patient must be left alone at the treatment unit for the radiation delivery.
Two types of targets are used in therapy machines:
(1) Reflection targets which are used on the low energy units.
(2) Transmission targets which are used on higher energy machines including linear accelerators.
Until the early to mid-1950s, most cancer patients undergoing radiation therapy were treated with
low-energy equipment. Physicians did their best with the equipment available to them, and surgery was still the treatment of choice for most cancers.
• These machines use x-ray energies in the range of
50 – 150 kilo-volts (kv).
Orthovoltage machines commonly have treatment distances of
50 – 70 cm. SSD and are not isocentric.
In orthovoltage or other low-energy treatments, treatment may be monitored directly through
leaded glass windows.
The beam that is produced consists of a
spectrum of photon energies.
Conventional low-energy equipment
• The use of this equipment dramatically
decreased after 1950.
• This decrease was in part the result of the increased popularity of cobalt-60 units and subsequent development of the linear accelerator.
• Treatment fields are usually defined by a cone and treatment distances are usually short, i.e.
15 – 20 cm SSD.
Most orthovoltage machines use a
collimator system (defines field) with a field light.
With megavoltage units indirect monitoring systems are used. To maintain patient safety and accuracy of treatment....
audio and visual contact is maintained at all times.
The photons used in conventional low-energy equipment are produced
with X ray machines
However, kilovoltage equipment is still used in many departments today, in part because...
of the low cost and simplicity of design compared with megavoltage units
• Superficial machines have filters, usually
aluminum, to remove the soft x-rays produced.
• Like the superficial units, orthovoltage units also have filters which
harden the beam and are called Thoraeus Filters.
Describe 3 key functions of the communication system
• A two-way communication system between the treatment room and console remains continuously audible to the operator.
• A switch allows communication into the treatment room when necessary.
• Demonstration of monitoring systems to new patients, reassures them that they are heard and seen during treatment delivery and that their privacy is being protected
The main components of a radiotherapeutic X-ray machine are:
• an X ray tube
• ceiling or floor mount for the X ray tube
• target cooling system
• control console
• an X-ray power generator.
--The primary application of kilovoltage equipment is
in the treatment of skin and superficial lesions
The process of removing the soft x-rays from a beam is called
beam hardening
--So called “soft x-rays” consist of low energy photons that are not desirable in the x-ray beam.
Thoraeus Filters. These filters contain:
Tin (Sn), Copper (Cu) and aluminum (Al). *
• Path of beam -----→ (Sn /Cu/Al) patient
During a treatment, patient comfort becomes non-essential.
False