Glossary of Terms
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
AVM (Arteriovenous Malformation)
An abnormal, congenital cluster of tangled blood vessels within the brain or spine that is at risk of bleeding. Depending on the AVM location, bleeding can cause symptoms ranging from headaches and seizures to paralysis and even death.
Benign Tumor
Benign tumors are not cancerous, ie do not spread to other areas of the body. However, their growth and enlargement can cause symptoms by compressing nearby tissue or structures such as nerves. Over time some benign tumors may become malignant.
Bite Block
A device used during stereotactic radiotherapy (SRT) treatment. A bite block is a mouth guard that affixes to the patient’s upper teeth. This device sometimes includes sophisticated markings (fiducials) that are tracked by an optical camera system. Bite blocks permit a patient to be re-positioned with a relative degree of accuracy on a repeat basis. However, it generally does not provide the level of accuracy that a stereotactic head frame or the CyberKnife’s image-guidance system provides for radiosurgical treatment.
Chemotherapy
Cancer treatment that is administered through the use of drugs that are injected into the body or taken orally over a period of time. This is a form of systemic therapy – ie as the drugs circulate in the bloodstream, the entire body is affected.
CNS (Central Nervous System)
The combination of the brain and spinal cord.
Conformal Radiosurgery
Radiosurgery procedures that shape a radiation beam to more closely conform to the tumor or lesion, rather than using the traditional method of multiple circular beams. Conformal radiosurgery maximizes radiation to the target and minimizes doses to surrounding healthy tissue.
Critical Structures
Refers to areas in the brain and nervous system that are responsible for vital functions such as memory, speech, hearing, sight, and movement. The spinal cord is the primary critical structure within the spine.
CT (Computerized Tomography)
A diagnostic imaging technique where an x-ray machine and computer are used to create detailed images of tissues and structures in the body. A dye, or contrast agent, may be injected into the patient to highlight abnormalities.
CyberKnife® Radiosurgery
Cleared by the FDA for full-body, 100% frameless radiosurgery. The CyberKnife® System utilizes a proprietary image-guidance system and a multi-jointed robotic arm that enables access to hard-to-reach tumors and reduces damage to surrounding healthy tissue. Integration of these unique technologies allows physicians to treat complex-shaped tumors and lesions that are inaccessible by surgery and other radiosurgical technologies. CyberKnife® radiosurgery involves a multidisciplinary team consisting of a surgeon, radiation oncologist, and a radiation physicist.
Fiducials
Fiducials are markings found on either the head frame or bite block. Additionally, x-ray visible fiducials may be surgically implanted for treatment of spinal or other tumors. The fiducials act as markers to precisely identify the location of a tumor or other target.
Fractionated Radiosurgery
See Staged Radiosurgery
Fractionation (sometimes called Staging)
Dividing the total dose of radiation into multiple smaller doses (usually administered daily), thereby permitting the surrounding exposed healthy tissue time to repair.
Gamma Knife
The Gamma Knife is the original radiosurgery technology, which by design is restricted to treating brain tumors. This device uses ionizing radiation (gamma rays) produced by 201 radioactive cobalt-60 sources to ablate intracranial targets.
Glioma
Tumors that arise from the supportive tissue of the brain. These are the most common primary brain tumors. Examples include astrocytoma, ependymoma, oligodendroglioma, and glioblastoma.
Head Frame (Stereotactic Head Frame)
An external metal ring that is affixed to the patient’s skull with four screws. It contains markings (fiducials) that are visualized on the CT and/or MRI scan. Local anesthesia is used during the frame attachment procedure. Nearly all radiosurgical techniques including the Gamma Knife use such head frames.
Image-Guidance System
The technology utilized by the CyberKnife® Radiosurgery system to track and verify tumor location, and enable automatic compensation for tumor movement. Image guidance technology allows for 100% frameless treatments without the use of a painful head frame.
IMRT
IMRT or Intensity Modulated Radiation Therapy is a form of three-dimensional conformal radiation therapy (3D-CRT) that incorporates beam-shaping to dynamically reshape the outlines and intensity of the radiation field during cancer treatment. IMRT fits the dose of radiation to a target much better than conventional radiation therapy, and thereby minimizes the volume of surrounding normal tissue that is injured by treatment. While it appears that IMRT may produce fewer side effects than conventional radiation therapy, IMRT is not as spatially precise as radiosurgery. Because of this imprecision, a full course of IMRT treatment is typically administered over multiple treatment sessions (typically 20-30+).
Inaccessible Tumor
A tumor that often cannot be removed surgically because it is located in an area that is difficult to access by open surgery. Because of location, surgical resection of these tumors has a high probability of damaging vital areas of the brain or spinal cord.
Intracranial
Refers to location “Inside the skull” or brain.
Isocentric Treatment Planning
All SRS devices (with the exception of the CyberKnife® System) are restricted to using a fixed isocenter as the standard for treatment.
Isocentric treatment - or multi-isocentric treatment - involves packing the lesion with a single - or multiple, overlapping - spherically shaped dose distributions.
Hot spots are areas where treatment volumes overlap, causing some tissue to be overdosed with radiation. Excessive radiation exposure of normal tissue increases the risk of complications, especially with critical structures such as the highly radiosensitive optic chiasm and acoustic nerves.
Cold spots are under-dosed areas within the target that receive a less than optimal amount of radiation dose. In situations of under-dosing, there is a risk that all tumor cells will not be destroyed.
Linac or Linear Accelerator
A Linac, or linear accelerator, is a large x-ray machine that delivers high energy x-rays for therapeutic irradiation of benign and malignant lesions throughout the body.
Lumbar puncture (also known as a Spinal Tap)
A procedure used to withdraw a small sample of cerebrospinal fluid from around the lower lumbar spinal cord. This fluid can be subsequently analyzed for abnormal cells and proteins.
Malignant
Malignant tumors are cancerous and are capable of spreading from one site in the body to another, usually via the bloodstream in a process called metastasis.
Meningiomas
Generally benign tumors that develop from the meninges, thick strong membranes that cover the brain.
Metastatic Tumor
A tumor arising from cancer cells that originate elsewhere in the body and travel to a new anatomic site through the bloodstream.
MRI (Magnetic Resonance Imaging)
An imaging technique that uses magnetic fields rather than x-rays to delineate structures in the body. MRI generally provides more detailed images of soft tissue anatomy (as opposed to bone) compared to CT. A dye may be injected prior to the scan to improve visualization of many tumors. MRI scans are painless.
Multi-jointed Robotic Arm
Six independent joints on the CyberKnife®’s robotic arm provides the greatest reach and flexibility, enabling the CyberKnife® to access virtually any location in space around a patient. The CyberKnife® is the only radiosurgical technology incorporating a robotic arm, thereby allowing access to previously unreachable tumors and minimizing damage to surrounding critical structures.
Non-Isocentric Treatment
Offered only with CyberKnife® radiosurgery. The CyberKnife® System's multi-jointed robotic arm enables the delivery of radiation for more complex-shaped lesions. The radiation beams are delivered from arbitrary points in the workspace to the lesion without intersecting a common point or isocenter. Non-isocentric treatment allows the CyberKnife® to “paint” the lesion volume with a nearly uniform dose while simultaneously helping to contour radiation away from nearby healthy tissue.
PET (Positron Emission Tomography)
An imaging technique that provides a picture of brain activity by measuring levels of injected glucose sugar "labeled" with a radioactive marker.
Primary Brain Tumor
A tumor arising from cells in the brain or surrounding tissue (in contrast to a metastatic tumor).
Rigid Immobilization
Typically refers to the use of an external metal frame that is attached to the skeleton and minimizes patient movement during radiosurgery. The CyberKnife® does not require rigid immobilization.
Spinal Tap
See Lumbar Puncture
Staged Radiosurgery
(sometimes called Fractionated Radiosurgery)
Delivers higher doses of focused radiation to a lesion over a series of 2-5 treatment sessions, thereby enabling a biologically more effective total dose to be administered. This is particularly beneficial for radiosurgical treatment of larger tumors and tumors located near critical structures. Each individual treatment is called a stage (or fraction).
Staging
See Fractionation
Stereotactic (Stereotaxis or Stereotaxy)
“Stereo” makes reference to one’s position within 3-dimensional space. Stereotaxy or stereotaxis is the science and practice of precisely locating a tumor within 3D space.
Stereotactic Radiosurgery (SRS)
This term refers to a class of procedures that accurately deliver a high dose of radiation, in one to five treatment sessions. SRS typically uses a stereotactic frame that is anchored to the patient’s skull for targeting and immobilization. In contrast, the CyberKnife® allows physicians to perform SRS without a stereotactic frame, which makes this procedure significantly less traumatic and painful for the patient.
Stereotactic Radiotherapy (SRT)
This technique delivers lower doses of focused radiation with stereotactic-like methods over multiple (as many as 30 to 40) treatment sessions. Each session is termed a fraction, and this type of treatment represents a type of “fractionated” therapy. A bite block that fixes to the patent’s upper teeth in combination with a specialized mask is oftentimes used in place of an invasive head frame for brain treatments.
Surgical Resection
Conventional open surgery (with a knife) to remove a tumor or other lesion.
Target Localization
Identifying the location of the target precisely in 3-D space.
Treatment Planning
Customizing the radiosurgery treatment parameters (such as radiation dose and shape of the field) to the individual patient using specialized software. The process is typically computer-based and involves integrating information from CT/MRI scans to delineate the target. The treating physician must define a specific dose and other key treatment parameters depending on pathology and the location of nearby critical structures. Typically the treating surgeon, radiation oncologist and medical physicist are all involved in this process.
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