Key Terms of Cancer Management and Radiation Therapy Practice

Comprehensive vocabulary terms related to cancer management and radiation therapy practice based on the lecture transcript.

Adenocarcinoma

Epithelial cells that are glandular, such as the tissue lining the stomach.

Adjuvant therapy

Use of one form of treatment in addition to another treatment.

Anaplastic

Pathologic description of cells describing a loss of differentiation and more primitive appearance.

AP/PA

A 2-field treatment with two parallel opposed beams entering from the anterior surface and posterior surface of the patient.

Benign

Tumors that are generally well differentiated and do not metastasize or invade surrounding normal tissue. Benign tumors are often encapsulated and slow growing.

Biopsy

Surgical removal of a small tissue sample from a solid tumor to determine the pathology for the diagnosis of disease.

Blocked field size

Equivalent rectangular field dimensions of the open treated area within the collimator field dimensions, often defined by multileaf collimator position.

Bolus

Tissue equivalent material that is usually placed on the patient to increase the skin dose and/or even out irregular contours in the patient

Boost fields

Fields that are used to deliver a high dose to a small volume, generally delivered to the gross tumor volume only, excluding regional lymph nodes and organs at risk (OAR).

Brachytherapy

Radiation treatment at a short distance accomplished by inserting radioactive sources directly into or near the tumor site.

Carcinoma in situ

Malignant changes at the cellular level in epithelial tissues without extension beyond the basement membrane.

Carcinomas

Tumors that originate from the epithelium and include all tissues that cover a surface or line a cavity.

Cellular differentiation

The degree to which a cell resembles its cell of origin in morphology and function.

A stem cell that undergoes mitosis & divides into daughter cells

Cerrobend

A form of Lipowitz metal used for shielding blocks consisting of $50.0\%$ bismuth, $26.7\%$ lead, $13.3\%$ tin, and $10.0\%$ cadmium.

Collimator

Arrangement of shielding material designed to define the "x" and "y" dimensions of the beam of radiation.

Collimator field size

Unblocked or open field size as defined by the collimator setting and projected at the reference distance, usually the isocenter.

Concomitant

Situation in which two types of treatment take place at the same time.

Cumulative Dose

A cumulative record of the dose received; for example, if the daily dose is $200\,cGy$, the cumulative dose after day 3 is $600\,cGy$.

Elapsed days

Total time over which radiation treatment is delivered (protracted).

Includes weekends,holidays (calendar dayss)

Electron Beam

A stream of small negatively charged particles generally used in the treatment of superficial lesions, lymph nodes, or scars.

Electron Cone

An extension added to the linear accelerator gantry when treating patients with electron beam therapy to help transport electrons towards the patient.

Electrons

Negatively charged subatomic particles that can be accelerated by machines or emitted from decaying isotopes for beam treatment or brachytherapy.

Epidemiology

Study of defining the distribution and determinants causing disease and injury in human populations.

Etiology

Study of the causes of disease.

Field size

Dimensions of a treatment field at the isocenter, usually represented by width $\times$ length.

Four Field Box

A treatment arrangement which includes AP, PA, Right Lateral, and Left Lateral treatment fields.

Fraction Dose or Size

The dose that is given in each fraction or treatment; the same as the tumor dose.

Fractionation

Radiation therapy treatments given in daily segments over an extended period of time, sometimes up to 6 to 8 weeks.

Gantry

A device on a linear accelerator responsible primarily for directing the photon (x-ray) or electron beam at a patient's tumor.

On a conventional simulator, it is a mechanical C-shaped device that supports the x-ray tube andcollimator device at one end. On a CT scanner, it is the circular ring housing the x-ray tube and solidstate detectors.

Image-guided radiation therapy (IGRT)

The process of imaging the patient just prior to treatment to compare the position of external set-up marks and internal anatomy to the treatment plan.

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.

Immobilization

Process of ensuring that a patient does not move out of treatment position, allowing for reproducibility and accuracy.

Immobilization device

Device that assists in reproducing the treatment position while restricting movement (e.g., casts, masks, or bite blocks).

Immunotherapy

Treatment with the goal to amplify the body's own disease fighting system to destroy the cancer.

Intensity modulated radiation therapy (IMRT)

Therapy that delivers nonuniform exposure across the radiation field using a variety of techniques and equipment.

Isocenter

Point of intersection of the three axes of rotation; for a modern linear accelerator, it is exactly $100\,cm$ from the radiation source.

This point is space becomes the axis around which the gantry, collimator and table rotate.

Isocentric technique

Approach to 3D treatment using multiple imaging modalities to plan where the isocenter is placed in or near the target volume.

Multiple Modalities including fluoroscopy, CT,MRI, PET, SPECT, and ultrasound

Lasers

Each positional laser projects a small red or green beam of light toward the patient during the

simulation or treatment process. This provides the therapist several external reference points in

relationship to the position of the isocente

Linear accelerator

Radiation therapy treatment unit that accelerates electrons and produces x-rays or electrons for treatment.

Malignant

Tumors that often invade and destroy normal surrounding tissue and, if left untreated, can cause the death of the host.

Metastases

The spread of cancer beyond the primary site.

Metastasize

Process of tumors spreading to a site in the body distant from the primary site.

Monitor unit (MU)

Unit of output measure used for linear accelerators. Accelerators

are calibrated so that 1 MU delivers 1cGy for a standard, reference field size at a standard reference depth at a standard source-to-calibration point

Multileaf collimator (MLC)

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 field shape by projecting 0.25 cm to 1 cm beam widths per rod as measured at isocenter.

Neoplasia

New growth.

Oblique Fields

Fields that enter the patient at an angle other than $90$ degrees.

Optical Distance Indicator (ODI)

A device that projects a scale of numbers on the patient so that an SSD reading can be obtained; also called a range finder.

Parallel-opposed field set

Two treatment fields that share common central axes and are $180$ degrees apart.

Pendant

Handheld local controls suspended from the ceiling or attached to the couch that mimic those of the treatment unit.

Photon

Small packet of electromagnetic energy, including radiowaves, visible light, x-rays, and gamma rays.

Photon Beam

A type of radiation therapy that uses x-rays or gamma rays that come from a special machine called a

linear accelerator (linac). The radiation dose is delivered at the surface of the body and goes into the

tumor and through the body. Photon beam radiation therapy is different from proton beam therapy.

Prescription

Radiation may be delivered only under the direct order of a radiation oncologist. Radiation orders are

written as prescriptions that must be signed by a radiation oncologist before the initiation of radiation

treatment (no exceptions!).

The prescription includes the anatomic site to be treated, the total radiation dose to be delivered with

its fractionation and protraction schedule. It also identifies the treatment technique to be used.

Radiation therapists check the prescriptions of patients every day to identify whether a change to the

prescription be implemented by the doctor

Protraction

The time over which a total dose of radiation is to be delivered.

Radiation Therapy Prescrption

Legal document written by a radiation oncologist that provides the therapist with the information

required to deliver the appropriate radiation treatment. It defines the treatment volume, intended

tumor dose, number of treatments, dose per treatment, and frequency of treatment.

Record & Verify System

A technology centered system which validates parameters from the treatment plan for treatment setup

and delivery. With this system, the machine settings are compared to the treatment plan data to ensure

all elements of the setup match the plan prior to treatment delivery. If a setting, like field size, gantry

angle, etc does not match the plan, the treatment unit is unable to be activated…..this is a safety

measure.

Sarcoma

Tumors arising from mesenchymal cells or connective tissue.

Shielding

Material used to limit the exposure to ionizing radiation.

Shrinking fields

Technique that reduces the treated field area one or more times during the course of treatment in

response to a tumor that reduces in size and/or the need to limit doses to normal structure

Simulation

In cancer treatment, a process used to plan radiation therapy so that the target area is precisely located

and marked. Today, CT simulation is the most common approach. In the past, simulation was performed

with a unit that allowed for radiographic and fluoroscopic imaging

Source-axis distance (SAD)

Distance from the source of radiation to the axis of rotation of the treatment unit.

Source-skin distance (SSD)

Distance from the source of radiation to the patient's skin.

Staging

Cancer is staged after a histologic diagnosis is made. Staging helps determine the anatomic extent of the

disease. Treatment decisions are based on the histologic diagnosis and extent of the disease.

Stereotactic radiosurgery (SRS)

Use of a high-energy photon beam with multiple ports of entry convergent on the target volume.

Three-dimensional conformal radiation therapy (3DCRT)

Three-dimensional image visualization and treatment-planning tools are used to conform isodose

distributions to target volumes while excluding normal tissues as much as possible.

Tissue Tolerance

The dose point that tissues can tolerate which, if exceeded, will lead to serious side effects or consequences.

Total Dose

The total dose the patient will receive at the conclusion of the treatment course.

Treatment Console

Operating center where timers and system-monitoring indicators are displayed.

Treatment couch

Part of the linear accelerator, the treatment couch is the area on which patients are positioned to

receive their radiation treatment. Some treatment couches provide six degrees of freedom to better

enable patient positioning and treatment delivery.

Treatment field (portal)

Volume exposed to radiation from a single radiation beam.

Treatment record

Documents the delivery of treatments, recording fractional and cumulative doses, machine settings,

verification imaging; and the ordering and implementation of prescribed changes.

Treatment Technique

Defined method by which a treatment is delivered to the patient

Tumor Dose

The dose prescribed to the tumor, representing the total of all dose delivered by each field or beam.

Tumor grade

Tumor grade is a specification that describes the apparent microscopic aggressiveness of the cancer as

determined by cytologic and morphologic criteria.

Tumor staging

Means of defining the tumor size and extension at the time of diagnosis. Tumor staging provides a

means of communication about tumors, helps in determining the best treatment, aids in predicting

prognosis, and provides a means for continuing research.

Wedge filter

Tool that modifies the isodose distribution of a beam to correct for oblique incidence or tissue

inhomogeneities by progressively decreasing beam intensity across the field irradiated.

X-ray

Electromagnetic radiation that is produced when a fast electron stream hits a target. Synergy of the

resultant x-ray beam increases with the voltage that accelerates the electron