Introduction to Clinical Rad Therapy & Operations Chapter 7

harmful incident (safety considerations)

(adverse event) is an incident that results in harm to a patient.

What are the major components of the Gantry?

- Electron Gun -Accelerator structure (Guide) -Treatment Head

Food and Drug Administration (FDA)

A governmental agency of the U.S. Department of Health and Human Services that is responsible for protecting and promoting public health through the regulation and supervision of food safety, tobacco products, dietary supplements, prescription and over-the-counter pharmaceutical drugs (medications), vaccines, biopharmaceuticals, blood transfusions, medical devices, electromagnetic radiation emitting devices (ERED), cosmetics, and veterinary products.

magnetron

A special type of electron tubes that are used to provide microwave power to accelerate electrons in a linear accelerator.

TomoTherapy

A treatment unit where the linear accelerator rotates continuously while the treatment couch moves through the gantry bore producing a spiral treatment beam.

When comparing MV prt films prior to the treatment, they are compared with what?

A. CT slices B. MRI Images C. DRRs D. X-Rays Answer= C

The Process of modifying the treatment beam profile to optimize the dose distribution through the treatment volume is called?

A. Intensity Modulation B. Dose volume modulation C. Computerized delivery D. Coplanar Beam Targeting Answer = A

The measurement of the thickness of a patient along the central axis or at any other specified point within the radiation volume refers to:

A. Simulation B. Localization C. Verification D. Separation Answer = D

Dynamic Method (IMRT)

Also known as a "Sliding window." The beam remains on as the MLCs andd gantry move throughout the treatment.

Optical Distance Indicator (ODI)

Also known as the "Range finder." displays a light with a scale in centimeters on the patient's surface to specify the SSD. Located on or near the collimator.

Patient safety incident

An event or circumstance that could have resulted, or did result, in unnecessary harm to a patient.

Near Miss

An event, circumstance, or incident that did not occur and was identified before treatment delivery.

If a patient is holding onto a wing board immobilization device, with that patient being in that position, what areas of treatment can we treat?

Anything below the neck since the arms are out of the way.

Wing Board immobilization Device

Arms are above the head. Each hand is holding a pole.

Digital reconstructed radiograph (DRR)

Based on acquired computed tomography (CT) information, these are images that render a beam's-eye-view display of the treatment field anatomy and areas of treatment interest. These images resemble conventional radiographs.

Anything pertaining to a Vac-Lok or Alpha cradle would be considered a?

Complex immobilization device

Source to Axis Distance (SAD)

Distance from the radiation source to the isocenter of the treatment machine. When the gantry rotates around the patient, the SSD continually changes; however, the SAD is at a fixed distance and will not change. (usually 100cm)

Source to Skin Distance (SSD)

Distance from the source of radiation to the patient's skin, usually measured using an Optical Distance Indicator (ODI) or rangefinder.

Multileaf collimator

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.

Stand

Drive stand appears as a large, rectangular cabinet, at least as large as the gantry. As its name indicates, the drive stand is a stand containing the apparatus that drives the linear accelerator.

EMR

Electronic Medical Record

Klystron

Equipment that converts kinetic energy to microwave energy in the linear accelerator.

Flattening Filter

Flattens the x-ray beam exiting the target

Clinical Target Volume (CTV)

GTV plus local margins for subclinical disease or regions of presumed microscopic disease

What 3 things on the Linear accelerator rotate at the isocenter?

Gantry, Collimator, and the base of the couch

Wedges

Help reduce hot spots in treatment plans with multiple fields with hinge angles less than 180

Waveguide

Hollow, tubelike structure within the linear accelerator that is used to transfer microwave power to the accelerator structure.

Carrousel

Houses scattering foils and flattening filter, moves specific component into beam as needed

Alpha Cradle

Immobilization cast made of a foaming agent like polyurethane and a Styrofoam base

Vac-Lok

Immobilization device that uses a vacuum and small beads of Styrofoam within a thick plastic bag

A fixing and immobilization device to the treatment couch for reproducibility is commonly referred to as?

Indexing

Monitor chambers

Ionization chambers in the treatment head that measure dose, beam flatness and symmetry

"IGRT" Image guided radiation therapy

It may be used in a variety of forms, including EPID, an in-room computed tomography (CT) scanner, kV cone-beam computed tomography, MV cone-beam computed tomography, ultrasound, and others. Rational for IGRT is to image the patient just before treatment and compare the position of external setup marks and internal anatomy to the treatment plan.

Secondary Collimator

Jaws of the machine, sets field size of the beam; often asymmetric

Transmission Filters

Limit a certain percentage of the beam to pass through at a certain location within the treatment field.

Isodose Lines

Lines connecting points of equivalent relative radiation dose.

Beam-Flattening Filter

Located on the carousel within the head of the linear accelerator. This high-density metal filter shapes the x-ray beam in its cross-sectional dimension, providing a more even dose distribution across the radiation field.

American Society of Radiologic Technologists (ASRT):

Mission of the ASRT is to foster the professional growth of radiologic technologists and radiation therapists by expanding knowledge through education, research, and analysis.

Scattering Foil

Most common method of producing an electron beam wide enough for clinical use is to use a scattering foil. Scattering foil is a thin sheet of a material that has a high Z number placed in the path of the "pencil beam" of electrons. Second scattering foil may be added to create a "dual scattering foil" arrangement. First scattering foil is used to widen the beam; the second is used to improve the flatness of the beam.

NCI

National Cancer Institute

NEMA

National Electrical Manufacturers Association

Organs at Risk

Normal tissues (critical structures) in which sensitivity to radiation damage may influence treatment planning and/or the delivery of a prescribed dose of radiation.

Organs at Risk (OAR)

Normal tissues (critical structures) in which sensitivity to radiation damage may influence treatment planning and/or the delivery of a prescribed dose of radiation.

Gantry

On a conventional simulator, it is a mechanical C-shaped device that supports the x-ray tube and collimator device at one end. On a computed tomography (CT) scanner, it is the circular ring housing the x-ray tube and solid-state detectors. On a linear accelerator, it is responsible primarily for directing the photon (x-ray) or electron beam at a patient's tumor.

Elapsed Days

On the first day of treatment there is no elapsed day (0). Every day from the start of treatment is counted. If the first treatment is on Friday and second treatment is on Monday there are 3 elapsed days (0-Friday, 1-Saturday, 2-Sunday, and 3-Monday). Every day between treatments (including scheduled breaks) must be counted. Elapsed days are continued while the patient is on break and when they resume treatment to a specific area.

Circulator

One of four major components housed in the drive stand, which prevents backflow of microwave power.

Gross Tumor Volume (GTV)

Palpable or visible extent of the tumor

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 6 degrees of freedom to better enable patient positioning and treatment delivery.

Target

Placed in electron beam to create an x-ray beam

American College of Radiology (ACR)

Professional medical association composed of diagnostic radiologists, radiation oncologists, interventional radiologists, nuclear medicine physicians, and medical physicists.

Surveilance, Epidemiology, and End Results (SEER) program.

Program initiated in 1973 to collect data in an effort to determine the epidemiology and etiology of cancer. symmetry: Maximum point-to-point difference in the central 80% of the profile.

Linear accelerator

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

Fractionation

Radiation therapy treatments given in daily fractions (segments) over an extended period of time, sometimes up to 6 to 8 weeks. Separating the doses; breaking it down.

Cobalt-60

Radioactive isotope with a half-life of 5.26 years that is used as a source for external-beam radiation therapy.

Electron Gun

Responsible for producing electrons and injecting them into the accelerator structure.

Interlocks

Safety switches blocking or terminating radiation production.

Primary collimator

Shapes the beam; sets maximum field size of the beam at isocenter

Microwaves

Similar to ordinary radio waves but have frequencies thousands of times higher. Microwave frequencies needed for linear accelerator operation are about 3 billion cycles per second (3000 MHz).

A pillow would be a?

Simple immobilization Device

accelerator structure

Structure resembles a length of pipe and is the basic element of the linear accelerator. Accelerator structure allows electrons produced from a hot cathode to gain energy until they exit the far end of the copper tube.

Maximum dose for various photon energies

Superficial: 0.0 Orthovoltage: 0.0 Cobalt-60: 0.5 4MV: 1.0 6MV: 1.5 10MV: 2.5 15MV: 3.0 20MV: 3.5 25MV: 5.0

Electronic Portal Image device (EPID)

System producing near real-time portal images on a computer screen for evaluation. Most electronic portal-imaging systems are lightweight and come with a retracted arm along the gantry's axis. Arm may be equipped with Amorphous Silicon (aSi) imaging technology, which provides a quick and accurate comparison of its images with reference images.

Dose Maximum (Dmax)

The depth of maximum buildup, in which 100% of the dose is deposited beneath the skin. Depth at which electronic equilibrium occurs for photon beams. This is also the depth of maximum absorbed dose and ionization, for photons, from a single treatment field. Depth of maximum ionization and maximum absorbed dose are usually not the same depth for electrons. See also Given Dose (GD).

Fixed versus rotational fields

The difference is whether or not the gantry is moving while the beam is on. Fixed means the angle is set, the beam is on, then the beam turns off and the gantry moves to the next angle. Rotational is where the gantry starts at certain angle and depending on the prescription dose and the dose rate, the gantry will stop and the beam will turn off at a certain angle.

When did installation of the first fully isocentric linear accelerator in the United States occur?

The first fully isocentric linear accelerator was manufactured and installed in the United States in 1961 by Varian Associates.

Isocenter (SAD) setup

The isocenter is established at some reference point inside the patient. the gantry (source) rotates around this point (axis). Since the field size is defined at the isocenter, the collimated field size is defined by the field size set inside the patient and not the field size on the skin surface as seen in the non-isocentric, SSD treatment setup. (SAD=SSD + Depth to isocenter)

SAD treatment

The patient is positioned so that the isocenter is located within the patient's body. The patient DOES NOT need to be moved between treatment fields.

Patient Alignment

The use of external landmarks (eyes, nose, sternal notch, xiphoid process, navel, legs) as well as the sagittal laser through middle of body can help to insure that the patient is straight on the table. The spine can be an effective way to straighten a patient when imaging is used. Adjustment of the patients hips or shoulders may be required.

Aquaplast

Thermoplastic mold

Triangulation

Three landmarks whose intersection marks a single reproducible point within a patient. Three reference points can confirm patient alignment in three planes (x,y,z). Shifts can be made from this location to another location within the patient.

Protraction

Time over which total dose is to be delivered.

Treatment Volume alignment on the machine often begins with what?

Triangulation

Dynamic Wedge

Use of a moving collimator jaw (X1, X2, Y1, Y2) to produce a wedged isodose distribution. (Also called a virtual wedge, used for computerized shaping of isodose curves within the treatment field.)

Bending Magnet

Used in high-energy linear accelerators to bend the electron stream within the head of the gantry, sometimes at right angles.

Immunotherapy

a cancer treatment that uses the body's defense system to fight cancerous tumors

stereotactic radiosurgery (SRS)

a noninvasive treatment in which high doses of focused radiation beams are delivered from several locations outside the body (Fig. 7.25). The objective is to minimize dose to the surrounding normal tissue.

Positive blocks

are blocks that shield more of the central part of the radiation field, leaving the periphery open. EX: lung blocks

Negative Blocks

are blocks that shield the periphery of the radiation field and the central portion is open. EX: electron cutouts

Forward planning for IMRT

beam parameters and modifiers are added to the treatment plan first and then the dose distribution is reviewed

IMRT (intensity modulated radiation therapy)

creates a nonuniform radiation beam in order to optimize the dose to the tumor while minimizing the dose to organs at risk near the tumor

DICOM (Digital Imaging and Communications in Medicine)

creates the standard format to transfer images from imaging computers to the treatment planning computer. It Allows us to communicate from doctor's office to doctor's office.

Machine parameters

energy used, gantry angles, table angle, collimator angle, field blocking, wedges, must be accurately recorded for treatment reproducibility.

Isocenter

fixed point in space where the central axes of the radiation beams intersect from every angle. The gantry, table and collimators all rotate around this point. Positioning lasers are aligned to intersect at this point. Generally set at 100cm from the radiation source for modern linear accelerators. The field size for a treatment unit is defined at the isocenter of the machine.

Image Guided Radiation Therapy (IGRT)

images the patient's soft tissue or tissue markers before treatment to verify an accurate treatment.

Beam Modifiers

includes blocks, compensators, and bolus

Cerrobend Blocks

involved in beam shaping

Graticule

is a calibrated device that is used to determine the setup distance.

Violation (safety considerations)

is a deliberate deviation from an operating procedure, standard, or rule. Both errors and violations increase risk, even if an incident does not actually occur.

Reportable circumstance (safety considerations)

is a situation in which there was significant potential for harm, but no incident occurred.

Adjuvant treatment

is a treatment given in addition to the primary treatment. Ex: Chemo & RT

patient safety incident (safety considerations)

is an event or circumstance that could have resulted, or did result, in unnecessary harm to a patient.

Near Miss (Safety considerations)

is an incident that did not reach the patient.

Volumetric Modulated Arc Therapy (VMAT)

is another type of CRT where a modulated beam is delivered through a rotational field.

Portal Imaging

is done before treatments start to verify the treatment plan and then at certain increments throughout the treatment as specified on the prescription. Taken in the beam's-eye view (BEV).

healthcare- associated harm (Safety considerations)

is harm arising from or associated with plans or actions taken during the provision of healthcare, rather than from an underlying disease or injury.

No harm incident (safety considerations)

is one in which an event reached a patient, but no discernable harm resulted.

Event (safety considerations)

is something that happens to or involves a patient.

An Error (safety considerations)

is the failure to carry out a planned action as intended or the application of an incorrect plan. Errors may manifest by doing the wrong thing (commission) or by failing to do the right thing (omission), at either the planning or execution phase.

PACS (Picture archiving and communication system)

is used to store and share images electronically. How we transfer images.

Sequential treatment

is when one treatment option follows another treatment (one after the other)

concomitant/concurrent treatment

is when two different kinds of treatments occur at the same time

Inverse Planning for IMRT

maximum dose to the tumor and maximum dose to organs at risk are defined

Electronic Portal Imaging Device (EPID)

newer technology that uses flat-panel x-ray detectors.EPIDs are ready to be reviewed immediately and do not have to be processed like films

Fixed (SSD) setup

patient is treated using a fixed distance from the radiation source (usually 100cm) to the patient's skin surface. The patient must be moved to this same distance between each treatment.

Hard Blocks

premade shields created with a high-density material

Arc/rotational therapy

rotational fields are also known as arc therapy, where the radiation is delivered while the gantry is moving in an arc from one set point to another

Cast Blocks

shields that are individualized for each patient

SBRT

stereotactic body radiation therapy

Step and shoot method (IMRT)

the beam is delivered with MLCs in one stationary position, turned off as the MLCs reposition to the next segment, and then turned back on.

SSD treatment

the patient's skin is placed at a fixed distance from the source. The patient must be moved in between treatment fields to maintain the fixed distance.

Inverse planning

the planner chooses the energy, appropriate dose to the tumor, and the tolerances of the normal healthy tissues

Forward Planning

the planner chooses the energy, number, shape, and direction of the radiation beams

Intraluminal implants

the source is placed within a body tube like the esophagus or bronchus

intravascular implants

the source is placed within a vessel and it avoids the narrowing of blood vessels after angioplasty

Intracavitary implants

the source is positioned within a body cavity

interstitial implants

the source is positioned within the tumor

Irradiated Volume

tissue volume which receives a dose that is considered significant in relation to normal tissue tolerance

parallel opposed portal/Fields (POP)

two treatment fields positioned 180 degrees apart.

Internal shields

used during electron therapy to shield critical structures that are located directly behind the tumor being treated

Lipowitz Metal

used for designing custom shielding blocks for photons and electrons and consists of 50.0% bismuth, 26.7 lead, 13.3% tin, and 10.0% cadmium

Bolus

used to eliminate skin-sparing effects in photon therapy. compensate for irregular surface contours, and eliminate air gaps in treatment fields. Made of materials similar to tissue or water. Must be prescribed by the physician and include the thickness and duration. Prescription must be changed if bolus is discontinued.

Treated volume

volume enclosed by an isodose surface (ex. 95% isodose) selected and specified by the radiation oncologist as being appropriate to achieve the purpose of treatment