Radiotherapy works by targeting high-energy gamma ray or electron beams onto cancer cells which are more prone to radiation damage than normal tissue. Refurbished linear accelerators are usually multi-modality ionizing radiation generators with associated imaging devices, currently used for delivery of external beam radiotherapy.

The contemporary linear accelerators provide either 6 MeV photons in the “low energy” range machines or dual/triple photon energy and several energies.

Systems Incorporated With Refurbished Linear Accelerators

• Multileaf Collimator (MLC) for beam shaping
• The capability to deliver intensity modulated radiotherapy (IMRT)
• 3D image guidance systems (IGRT)
• Electronic portal imaging system for image treatment beams

Other additional features may be incorporated into the linear accelerators such as arc-based IMRT delivery, total body irradiation, high-dose rate electrons, and more.  Despite the high capital cost of purchasing them, their high patient turnover throughout over a long lifespan makes them extremely cost-effective compared with other treatment options.

The operation of refurbished linear accelerators should be according to the existing standards and regulations which include:

• IEC standards
• Radiation regulations
• Guidelines for radiotherapy room design

Technical Considerations

The technology used in refurbished linear accelerators is essentially the same for all linear accelerators.  The high energy generation can be achieved either by implanting the “traveling waveguide technology” or by implementing the “standing waveguide technology”.

The first approach is simpler and very reliable, while the second approach features a more stable treatment beam.  The generated radiation beam is flattened and shaped using collimation devices to form a beam matching the shape of the tumor.  The wave guide, the filters, and the collimator are all mounted on a gantry which rotates around the patient, allowing the tumor to be irradiated from multiple directions.  There is a linear accelerator patient coach especially designed to allow irradiation of the patient from multiple directions.

Modern linear accelerators are designed to enable intensity-modulated radiotherapy (IMRT).  This is a dynamic radiotherapy delivery method which enables good control over the three dimensional dose distributions: the delivered beam instead of being flat changes the intensity at different points within the beam.

There are different types of refurbished linear accelerators IMRT delivery methods:

• Step and Shoot Method: consists of delivering a series of different shaped fields formed by the MLC to build up a variable intensity pattern. The irradiation is stopped between the fields.
• Dynamic MLC Method: in which the radiation runs constant, while the MLC leaves move across the field at variable speeds.
• Arc Therapy Method: in which the radiation runs continuously and the gantry collimators and MLC leaves are all moving continuously. The dose rate also varies during the delivery.  Treatments are delivered in an arc, sometimes two.  This is probably the best choice for IMRT.

The multi-leaf collimator is a delicate computer-controlled mechanism.  The performance of the collimator depends on its resolution, the leakage radiation and the system penumbra.

The electronic portal imaging device allows verification of patient position on orthogonal two-dimensional images produced by the high-energy treatment beam.  The detector used for the portal imaging consists of an amorphous silicon indirect detection flat panel imager.

The imager system differs in the degree of complexity of software provided, as well as the ease of use.  The refurbished linear accelerators’ three-dimensional imaging systems can be materialized in three different ways:

• 1) Applying diagnostic x-ray cone beam, in plain or orthogonal to the linear accelerators’ high energy beam.
• 2) Using the high-energy treatment cone beam of the linear accelerator.
• 3) Using a CT machine combined with the linear accelerator.

Record and Verify Systems

In modern radiotherapy departments, the refurbished linear accelerators are operated using record and verify systems, which deliver the treatments, as well as make a record of them.  These systems are usually connected to the general information network, which allows a wide functionality, including booking and scheduling, recording of patient’s notes, recording costs, image handling, and more.

Acceletronics is an independent service company dedicated to delivering the best equipment performance and service reliability from Linear Accelerators and CT Scanners across all major brands and models. Learn more about Acceletronics and their selection of new and refurbished linear accelerators and CT scanners today at http://www.acceletronics.com.  To contact one of our LINAC experts call 610.524.3300.