Radiation Therapy

Varian Trilogy Linear Accelerator

The Varian Trilogy Stereotactic System is at the cutting edge of cancer therapy. As the leading image-guided radiotherapy (IGRT) system, the Trilogy marks the beginning of a new generation of cancer care. The versatile Trilogy system can be used to deliver the widest range of external beam radiotherapy: Intensity-Modulated Radiation Therapy (IMRT) , Stereotactic Radiation Therapy (SRT), 3D Conformal Radiotherapy, and Electron Beam Radiation Therapy for cancer and neurosurgical treatments.

Advanced imaging capabilities built into the system allow technicians to position patients for treatment with sub-millimeter accuracy, making sure the tumor is lined up precisely with the treatment beam before the beam is turned on. A respiratory gating system takes into account the tumor movement that can occur as a patient breathes, turning the beam on and off, so that treatment is delivered only when the tumor is stationary.

This advanced linear accelerator enhances delivery of radiation therapy and reduces adverse side effects in patients thanks to increased accuracy in focusing the beam on the tumor and sparing normal tissue. It also allows us to offer stereotactic radiation therapy, a new form of targeted therapy that can be administered over days, instead of weeks. This exciting new technology is being used to treat many cancers including osteosarcomas, nasal tumors, and brain tumors.

Intensity-Modulated Radiation Therapy

Intensity-modulated radiation therapy (IMRT) is a state-of-the-art cancer treatment method that delivers high doses of radiation directly to cancer cells in a very targeted way, much more precisely than is possible with conventional radiotherapy. IMRT involves varying (or modulating) the intensity of the radiation beam, so that the shape of the resulting dose distribution is tightly matched to the shape of the tumor. IMRT enables an oncology team to direct and narrowly concentrate potent doses of high-energy X-rays at a patients tumor while minimizing complications to surrounding healthy tissue.

IMRT targets a tumor with intensity-modulated beams delivered from multiple angles. The area where the radiation beams intersect creates a finely sculpted radiation cloud that envelops and has the same shape as the tumor. The IMRT process starts with diagnostic images; for example, computed tomography (CT), magnetic resonance imaging (MRI) and/or positron emission tomography (PET) images, of the patient's tumor and surrounding anatomy. These images are converted into a custom three-dimensional model of the patient's internal anatomy. A powerful computer program creates a treatment plan based on tumor size, shape, and location within the body, along with the veterinarian's dose prescription.

A medical linear accelerator, equipped with a special beam-shaping device called a multileaf collimator (MLC), delivers the radiation in accordance with the treatment plan. The Varian high-resolution MLC has 120 tungsten metal leaves or slats for shaping the radiation beam to deliver unique doses to areas as small as the tip of a pencil.

The linear accelerator rotates around the patient to send beams from multiple angles in order to give the tumor a high dose of radiation while preserving important healthy tissues. A powerful computer program guides the movement of the linear accellerator and the MLC to precisely match the treatment plan, delivering the correct dose directly to the target.

Patient Benefits
Higher doses of radiation can be delivered directly to tumors and cancer cells, while surrounding organs and tissues are protected. Lower doses to healthy normal tissues means fewer complications or side effects. For example, in the case of head and neck tumors, IMRT allows radiation to be delivered in a way that minimizes exposure of the spinal cord, optic nerve, salivary glands or other important structures. In the case of prostate cancer, exposure of the nearby bladder or rectum can be minimized.

The level of normal tissue sparing achieved with IMRT is dramatic. Clinical experience shows a tremendous reduction in the side effects of radiotherapy when IMRT is used.

Clinicians can treat cancers that were previously untreatable with radiation therapy, sparing some patients the invasive techniques of surgery and/or chemotherapy.

Stereotactic Radiation Therapy

Stereotactic radiation therapy (SRT) is also called stereotactic radiosurgery, gamma knife therapy, or cyberknife therapy. There is no surgery involved, rather it got the name because the radiation is a precise as a scalpel at focusing on the tumor. SRT protocols generally are delivered in 1-5 fractions (doses) on consecutive or alternating days.

This method is ideal for treating pituitary tumors, inoperable menigiomas, other brain tumors, osteosarcomas, nasal tumors, liver tumors, and for palliation of tumors in the abdominal cavity.

SRT requires special radiation therapy equipment that has the ability to confirm the location of the patient and tumor right before therapy. This is the stereotactic aspect that the Trilogy provides.

High doses of radiation are delivered using a very precise beam during a single treatment session. It is generally used for smaller lesions and metastases. Historically, this approach was used primarily in neurosurgery for treating brain lesions and abnormalities. However, the Trilogy system also is optimized to deliver stereotactic radiation therapy to tumors in the body.

Targeting tumors requires highly accurate patient positioning and immobilization. Patients are positioned using a variety of immobilization devices, depending on the location of the tumor. Multiple beams are used in a similar fashion to IMRT.

For some tumors, SRT can be used with curative intent. For other tumors, it is used for palliation, but for far more durable palliation than can be achieved using traditional methods. SRT is easier on the patient and client because treatment can be completed in such a short period of time and acute radiation effects are minimal. However, it is not indicated for all tumor types and locations. Ask your oncologist if this is an option for your pet.

Patient benefits include:

• The use of powerful beams means reduced treatment time.
• The most accurate beam means the most accurate treatment.
• The most advanced patient positioning tools mean the most accurate treatment and a reduction in side effects.
• The ability to deliver treatments that shrink-wrap the radiation dose to the tumor means a reduction in the side effects of the treatment.
• Treatment is generally completed in one to five days.
• Acute radiation effects are minimal.

3-D Conformal Radiotherapy

Three-Dimensional Conformal Radiation Therapy uses CT-based techniques to generate 3-D images of internal structures. The volumes are used to shape radiation beams to spare normal tissue. This remains a useful tool in the delivery of radiation therapy.

Electron Beam Radiation Therapy

Electron therapy is a form of external beam radiation therapy where electrons are directed at the tumor. Electrons don't penetrate as deeply as X-rays, which are normally used for external beam radiation therapy. This makes electrons well suited for treating tumors close to the skin's surface.

Electrons are particularly useful for treatment of skin tumors over the abdomen, ensuring that excess radiation dose not reach the intestinal tract; and for limiting the dose of radiation to the lungs for tumors over the thorax.

Electrons also are useful for tumors near the eye. A special ceramic-covered tungsten contact lens block can be placed over the eye to greatly diminish dose, while the prescribed dose can be delivered to the area surrounding the eye. At CSU, we have electrons ranging in energy from 4-18 MeV. The energy selected for each patient is based on the thickness of the area being treated.