Chapter 8 worksheet

Graticule

A bb tray or dot tray is a calibrated device. It fits into the collimator and provides radiographic representation of the central ray, aperture size, rotation, and magnification of the treatment aperture on the digital radiograph

Cerrobend

A form of Lipowitz metal used for designing custom shielding blocks and electron cut-outs and consists of ... Glossary Bismuth 50%, Lead 26.7%, Tin 13.3%, Cadmium 10% Cadmium and lead are toxic

What is included in the prescription

Anatomic site Total dose to be delivered with its fractionation and protraction schedule. Treatment technique (number, type and orientation of treatment fields) to be applied Information specifying beam energy, portal sizes, and entry angles, and beam modifiers Patient positioning info.

Collimation

Arranging the the shielding material designed to define the X and Y dimensions of the beam of radiation.

Wedges (Referred to as hard or physical wedges)

Beam modifier designed to change the angle of the isodose curve relative to the beam axis at a specified depth within the patient. Reduce the dose in areas of overlap between fields that have hinge angles less than 180 degrees. The thick end of the wedge (heel) attenuates the greatest amount of radiation, thus drawing the isodose lines closer to the surface The thin end of the wedge (toe) attenuates less of the radiation, thus delivering a greater dose at the opposite side of the treatment field. Standard wedges sizes are: 15,30,45,60 degrees The purpose is to better distribute the isodose lines of radiation to prevent against `cold` or `hot` spots of variable doses.

Compensators

Beam modifier that changes radiation output relative to loss of attenuation over a changing patient contour.

Immobilization devices

Devices that assist in reproducing the treatment position while restricting movement. Masks, bit blocks, vac bags

Beam modifiers

Devices that change the shape of the treatment field or distribution of radiation at depth.

EPID

Electronic portal imaging devices System producing near real-time portal images on a computer screen for evaluation. Mounted opposite the head of the gantry (MV)

Fiducial markers

Fixed reference points against which other objects can be measured. Fiducial markers may include natural anatomy or be artificial markers placed internally or at the skin surface or fixed external to the patient to document location through various imaging modalities.

Localization

Geometrical definition of the tumor and anatomic structures using surface and/or fiducial marks for reference. Glossary Idendification of hidden anatomy relative to observable or palpable surface landmarks

IGRT

Image guided radiation therapy. It may be used in a variety of forms, including EPID, an in-room CT scanner, KV cone beam computed tomography, MV cone beam computed tomography, ultrasound and others. Purpose is to image the patient just prior to treatment, compare the position of external set-up marks and internal anatomy to the treatment plan.

Fractionation

Individual treatment dose (division of the total dose of radiation into small doses given at intervals) Radiation therapy treatments given in daily fractions (segments) over an extended period of time, Glossary Hyperfractionation delivers smaller doses than conventional, delivered two or three times daily to achieve an increase in the total dose in the same overall time. Hypofractionation delivers a larger doses than conventional over a shorter period of time.

Treatment isocenter

Is Hidden within the patient

Bolus

Materials that interact with the radiation beam in a way that mimics tissue. Tissue equivalent material that is usually placed on the patient to increase the skin dose and/or even out irregular contours in the patient. Ex. supraflab, paraffix wax, vaseline gauze, wet gauze or towels, and water bags

Hinge angle

Measure of the angle between central rays of two intersecting treatment beams. If a lateral and anteriorposterior beam intersect at the isocenter, the hinge angle would be 90 degrees.

Universal Precaution

Method of infection control in which any human blood or body fluid is treated as if it were known to be infectious.

MLC

Multileaf collimators Distinct part of the linear accelerator that allows treatment field shaping and blocking through the use of motorized leaves in the head of the machine. Usually made of tungsten, these metal collimator rods slide into place to form the desired shape by projecting .25cm to 1cm beam width per rod as measured at isocenter.

Treatment Technique

Number, type, and orientation of treatment fields to be applied.

Portal Imaging (may still be called port films at clinic)

Portal verification, documentation of treatment portals through radiographic images or electronic portal imaging devices.

Virtual Wedge

Replaces physical wedges. A moving jaw starts at one side of the treatment field and opens to the full field over the beam exposure. The dose if effectively sloped over the field, in the manner of a physical wedge. The side of the field at which the jaw starts its movement receives more exposure correlating with wedge toe.

Interlocks

Safety switch blocking or terminating radiation production.

V&R system

System that provides validated parameters from the treatment plan to the treatment machine for setup and delivery. Actual machine settings are compared with those most recently prescribed for a particular field and prevent initiation of the treatment beam if settings vary outside a specified tolerance range. Monitors, Mus, gantry position, collimator and aperture settings, table position, arc vs fixed treatment, beam modifiers and patient identification, accessories attached Ex. ARIA and Mosaiq

Machine isocenter

The point of axes for the gantry, collimator and base of couch. A static position with the treatment room.

Triangulation

Treatment isocenter is located relative to three setup coordinates on the patient's surface or on the equipment fixed relative to their anatomy.

Orthogonal images

Two images taken 90 degrees apart. They may be required for treatment-planning purposes to define the location and relationship of various anatomic structures relative to the field's isocenter.

Beam's eye view

Visualization perspective that is "end-on" or positioned as if looking at a volume from the source of radiation.

Wedge pair

a technique used to change the volume receiving radiation by decreasing the hinge angle between two treatment fields.

Treatment Record

contains the prescription, treatment plan Documents the delivery of treatments, Displays fractional and cumulative doses, machine settings, and verification imaging, the ordering and execution of prescribed changes Date of treatment Treatment number Elapsed days Daily fraction Fraction time intervals (e.g., hyperfractionation) Cumulative dose Notation of any change (e.g., verification imaging)

Treatment devices

ex. Blocks, Wedges, bolus, and compensators

Protraction

time period during which the treatment will be given Glossary

Portal

treatment field (volume of tissue exposed to radiation from a single radiation beam)