UK TomoTherapy Centers & Glossary

Glossary

Adaptive Radiotherapy (ART)

Changing a treatment plan between (or even within) treatment fractions, based on feedback received from TomoTherapy^® Hi·Art^® treatment system measurements and processes.

Beamlet

A beamlet is a single “element” of a beam, which in turn is one of hundreds of beams within a typical helical TomoTherapy delivery. A single beamlet corresponds to the radiation emitted through a single open MLC leaf, with the gantry at any given angle during rotation.

Collimation

The process of shaping a therapeutic beam by using materials that are opaque to it. These materials are placed in front of part of the beam to define the shape of the beam.

Collimator

The device used for collimation. The Hi·Art treatment system has two collimating devices: the primary collimator, or jaws; and the multileaf collimator (MLC).

Conformal Avoidance Radiotherapy (CA)

A form of IMRT used for cases where the tumor boundary cannot be easily defined. Rather than trying to map the precise area to be treated, clinicians can map out critical structures that must be avoided. Used in cases such as Hodgkin’s disease or tumors of the head and neck, this “everything but” strategy is central to treatments using the TomoTherapy Hi·Art system.

Conformal Radiotherapy

The goal of conformal therapy is to deliver a high dose to a volume that closely conforms to the shape of the patient’s tumor volume. It requires the ability to accurately identify both the exact shape and location of the tumor so as to distribute the dose as close as possible to the margin around the target.

CTrue™

The Hi·Art treatment system’s integrated, true CT imaging technology, which can be used for every patient, every day^™—for patient positioning, image-guided radiation therapy, dose targeting and adaptive radiotherapy.

Deformable Dose Registration

Using anatomical, biomechanical and ROI information to map changes in the patient’s anatomy between each fraction, deformable dose registration can map the reconstructed dose for each fraction back to a reference image. These mapped doses can then be added to obtain an accurate cumulative dose.

Delivery Modification

Changing the delivery pattern to compensate for any changes in the patient’s position or the location of the tumor between fractions. Instead of physically repositioning the patient (which can be a time-consuming and error-prone procedure), delivery modification can recalculate the delivery pattern based on the patient’s displacement.

Delivery Verification

Using a signal measured at the exit detector, delivery verification computes the energy fluence directed toward the patient. This information can be used to monitor the delivery and help to shut down the RT unit when delivery errors are detected.

DICOM

Digital Imaging and Communications in Medicine. An international communications standard developed by NEMA that defines the format used to transfer medical image-related data between different pieces of medical equipment. DICOM RT refers to the standards that are specific to radiotherapy data. The TomoTherapy Hi·Art treatment system uses both general and RT-specific parts of the DICOM standard.

Dose Reconstruction

Calculating the dose deposited on the patient by using delivery verification and a CT obtained at the time of treatment (fraction CT).

Fan Beam

A narrow, slit-shaped divergent beam. The TomoTherapy Hi·Art treatment system delivers therapeutic radiotherapy in the shape of a fan beam.

Fractionation

Splitting up the patient’s dose prescription into a number of different sessions, each of which delivers a fraction of the total prescribed dose.

Image-Guided Radiation Therapy (IGRT)

Radiation treatment guided by imaging technology such as CT scans, MRI’s, or PET scans. Clinicians use the Hi·Art system’s CTrue scans to verify the patient’s position, anatomy and tumor site at the time of treatment, helping ensure the accuracy of each treatment procedure.

Image Registration

A method for positioning the patient for each fraction of treatment on the TomoTherapy Hi·Art system. The clinician obtains a CTrue image of the patient, then superimposes that image over a reference image. The planning image can then be manually or automatically adjusted to get the best match.

Intensity-Modulated Radiotherapy (IMRT)

One of the most important recent advances in radiation treatment, IMRT involves changing the size, shape, and intensity of the radiation beam to conform to the size, shape, and location of the patient’s tumor. The TomoTherapy Hi·Art treatment system uses a patented multileaf collimator to modulate the intensity of the radiation beam so that it precisely conforms to the shape of the tumor.

Inverse Treatment Planning

See Optimized Treatment Planning.

Linear Accelerator (linac)

A device that uses a number of chambers, each of which adds energy to electrons, accelerating them to high energies in the megavoltage range. The linac directs the high-energy electrons to a target, with which they collide to produce high-energy photons.

Multileaf Collimator (MLC)

A device that opens and closes individual leaves to regulate the amount of MV radiation passing through to the patient.

MVCT

Megavoltage computed tomography. See CTrue.

Optimized Treatment Planning

A process in which the appropriate beam pattern, position, and intensity are calculated based on the physician’s prescription for how much radiation the tumor should receive, as well as acceptable levels for surrounding structures. From the clinicians’ perspective, treatment optimization is easier and more accurate than conventional treatment planning. It is fundamental to the TomoTherapy Hi·Art treatment system.

Pencil Beam

Radiation passing through a single open leaf of the MLC.

Prescription

A formula for the preparation and administration of any remedy. In radiotherapy, a prescription usually defines the dose (in Gy) to be deposited on the tumor as well as the constraints for radiation deposited on surrounding sensitive structures. For example, a prescription for treating a prostate tumor might indicate 75 Gy to 90% of the tumor volume and no more than 30 Gy to 25% of an RAR such as the bladder or rectum.

Radiotherapy (RT)

Also called radiation therapy, radiotherapy is the treatment of cancer and other diseases with ionizing radiation, with the aim to damage primarily cells in the area being treated (the “target tissue”). Although radiation damages both cancer cells and normal cells, normal cells can repair themselves more quickly, while the cancer cells sustain more and more damage with each fraction of treatment.

Region of Interest (ROI)

An area of the patient’s anatomy encompassing the target (tumor) and/or any surrounding sensitive structures (Regions at Risk, or RARs).

Region at Risk (RAR)

Sensitive structures where the radiation dose must be minimized. An RAR is one component of Regions of Interest (ROIs).

Registration in Projection Space

A method for positioning the patient for each fraction of treatment using sinograms (the data from which a CT image is constructed). RPS compares the sinogram of the CT for the current fraction to a reference sinogram, calculating the difference without reconstructing the images themselves. Potentially faster than Image Registration, but less visually intuitive.

Target

The area (usually a tumor) to receive the prescribed dose of therapeutic radiation.

Tomography

The procedure used to obtain a set of slice images of the patient.

Posted by: Greg Lance-Watkins