Radiation therapy chap. 8

Baseline shift

Steady position change 

V&R systems

A Verify and Record (V&R) system in radiation therapy is an automated safety and management software framework that checks treatment parameters against the prescription before allowing a linear accelerator or other machine to deliver radiation

Beam Modifiers

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

BEV

Beam’s eye view 

Collimation

Arrangement of shielding material designed to define the X&Y dimensions of the field 

Compensator

Skin sparing for irregular surfaces 

Conformal therapy

applies 3-dimensional tumor volume localization to treatment field definition 

Coplanar

aligned with the gantry rotation plane

Elapsed days

Total time over which treatment is protracted. 

En-face

Directly facing 

Feathering

Adjusting junction lines between adjacent fields 

Fiducial

Placed object used as a point of reference 

Fraction

Individual dose intended for a treatment session. 

Hinge angle

Angle between two intersecting treatment beams’ central rays 

IGRT

Image guided radiation therapy 

Immobilization devices

Devices that restrict movement such as casts, masks, and or bite blocks 

IMRT

Intensity-modulated radiation therapy—Delivers non uniform, modulated exposure across the BEV 

Indexing:

Fixed, incremented PSA positions 

Interlocks:

Prevent beam initiation and include alerts prompting treatment setup and safety procedure completion 

Interfraction

Between treatment sessions 

Intrafraction

During a treatment session 

Isocenter and PSA

The intersection point for the linac’s three axes rotation (gantry, collimator, and patient support assembly--PSA also referred to as couch or table base) 

Localization

Hidden anatomy identification relative to observable or palpable surface landmarks. 

Meterset

Measurement unit for the machine delivered by monitor units or time. 

Method of delivery

Minimally, photons, electrons, or identifying an isotope 

Noncoplanar

not aligned with gantry rotation plane 

Orthogonal images

two beams perpendicular to one another with a 90° angle between them 

Protraction

time over which the treatment will be given 

SABR

stereotactic ablative radiation 

SBRT

Stereotactic body radiation therapy 

SGRT

Surface guided radiation therapy--Allows therapists to have less initial setup variability, helps provide verification of immobilization of the patient throughout treatment, and provides real time surface information for use in treatments requiring gating or breath holds. 

Stereoscopic

Two planar images from different angles focused on the same point 

Topographic Anatomy:

Relationships between anatomic structures in a region 

Treatment Field:

Tissue volume exposed to radiation from a single radiation beam 

Treatment history Record:

information about the patient’s treatment history 

Triangulation:

Three point 

Universal Precautions:

Infection control methods in which any human blood or body fluid is treated as if it were known to be infectious 

Universal protocol:

Pre-procedure verification, marked procedure site, timeout. 

Verification Imaging:

planar or CT images that confirm treatment setup 

VMAT:

Volumetric-modulated arc therapy 

How often is the radiation chart reviewed?

prior to treatment start and at least weekly during a treatment course. 

The chart must be current and accurate and contain... 

• Treatment rationale 

• Informed consent 

• Treatment plan 

• Treatment delivery records. 

the final part of the patient’s chart. 

planar or CT images (verification imaging)

Verification documents treatment…

localization reproduction. 

patient information necessary for treatment reproduction. 

Birth date, Identification image, street address, and phone number

Confirm patient identity using at least __ methods. 

2

Pre-procedure verification:

verify procedure, patient site, identify items which must be available for procedure, and match items to patient.  

DVH

Dose volume histogram

ODI

Optical Distance indicator

The Joint Commission requires accredited organizations to comply with the universal protocol and time out procedure: (3)

Pre-procedure verification

Mark procedure site

Timeout

Timeout 

• standardized process within organization 

• initiated by a designated team member at every instance  

• immediate team members performing the procedure actively communicating  

• correct patient confirmed using at least two methods  

• correct site, markings verified new line correct procedure to be undertaken 

• Document, organization determines form and amount 

Radiation orders are written as ________ that must be signed by the ______ _______before treatment begins 

prescriptions, radiation oncologist

prescription components include:

protraction (or time over which the treatment will be given) schedule, planning instructions, information specifying beam energy, portal sizes and energy angles, and beam modifiers with patient positioning information 

Dose distributions and meterset calculations, typically prepared by the medical ________, are reviewed and signed by at least ___ treatment planning team members before being made available for treatment. Before treatment, radiation therapists independently review the treatment plan for calculation factor _______ against treatment parameters.” 

dosimetrist, two, faithfulness

Treatment room design may be viewed as…

radiating outward from the isocenter

Before the patient arrives, radiation therapists must review…

treatment setup dimensions, field size, gantry, collimator, and PSA positions.  

• A beam aperture set, in the gantry position so that _____ are visible at the ________ and the field light crosshairs project in a vertical or horizontal direction. 

• The treatment ___ is raised or lowered appropriate to the patient's transportation method.  

• Position the PSA window where treatment fields will reach the patient without _______ the PSA. 

• _____covers the PSA windows supporting the patient without _______ the treatment beam.  

• Support may be enhanced by carbon fiber supports beneath the _____

• lasers, isocenter, PSA, intercepting, mylar, attenuating, mylar. 

Since comfort affects the patient's ability to maintain a treatment position…

headrests, leg sponges, and immobilization devices are used to support the elected position 

The treatment session positioning goal is…

planned position reproduction 

Landmark alignment with internal targets relies on _______ ___ ________ ______; Even slight body position variation can mean significant _______ with the internal location a surface landmark represents. 

vertical and horizontal planes, discrepancies

What moves with, and is hidden within the patient?

Treatment isocenter

Landmarks include…

natural anatomy or artificial fiducials positioned at a fixed relationship to unseen anatomy. 

Surface landmarks include…

visible and palpable anatomy 

Fiducials may be…

permanent or semi-permanent at the skin's surface, internal, or fixed external to the patient 

To align the patient to the isocenter, the patient will be raised on the treatment ___ until the _____ side lasers coincide with the patient marks on the right and left side 

PSA, lateral

X=

left and right

Y=

in and out

Z=

depth

SGRT offers opportunities to eliminate…

skin marks

This system allows for continuous monitoring of patient positioning during treatment, which helps improve patient safety and comfortability while also streamlining workflows for radiation therapists.  

SGRT

SGRT utilizes optical surface imaging and achieves small margins and a lower dose in three ways: 

1. By reducing intrafraction setup uncertainty 

2. By monitoring intrafraction movement 

3. By enabling respiratory treatments to involve gating and or breath hold techniques 

Stereoscopic images are…

two planar images from different angles focused on the same point 

Accuracy _____ as beam coincidence _____

increases, decreases  

orthogonal images are two beams _______ to one another with a __ angle between them.  

perpendicular, 90°

Strategies for managing tumor motion during treatment include:

free breathing, compression, breath hold, gating, and tracking 

gating systems actively monitor…

target positions, stopping the beam as the target moves out of range. The beam may be restarted when the target returns to range or the PSA may be adjusted to correct for a steady position change, a baseline shift 

Once isocenter coincidence is accepted…

rotate the gantry to the projection angle for treatment initiation 

Because neither people nor tumors present in squares or rectangles, treatment plans generally require…

further treatment aperture shaping 

Linear accelerators equipped with MLC (______) systems customize field shapes using ____ sliced into leaf banks where opposing leaf banks form leaf pairs. Leaf pairs quickly and flexibly produce _____ treatment field shapes 

(multi-leaf collimators), jaws, complex

Portal images verify…

the BEV path, the beam shape, and projection using the MV (megavoltage) treatment beam 

Portal images use…

single or double exposure techniques 

materials whose interactions with the radiation beam mimic tissue 

Bolus

Skin sparing for irregular surfaces can be preserved using a ______

compensator

Composed of copper, brass, lead, or Lucite, compensators are positioned in the treatment machine head with a minimum of __ centimeters between the compensator and the patient service. The air gap allows _______ scatter absorption, preserving skin sparing

15, electrons

These are Designed to change the isodose angle relative to the beam axis at a specified depth within the patient 

wedges

thick end of wedge:

heel

thin end of wedge

toe

standard wedge sizes:

15, 30, 45, and 60 degrees 

At least ___ cameras maintained visual contact with the patient 

two

These prevent beam initiation and include alerts prompting treatment setup and safety procedure completion.

interlocks

Options for beam interruption by the radiation therapist include…

pressing a beam off button, turning the operation key to the off position, or opening the treatment unit door. If these actions fail to stop the beam, an emergency off switch must be available, completely turning off the treatment unit. 

Most treatment plans require radiation delivery through _____ ports to achieve optimal dose homogeneity through the target volumes 

multiple

the most basic multiple field technique is the…

parallel opposed portal (POP).

The hinge angle for POP fields equals:

180° 

___ ______ demonstrates the ultimate multiple field technique, and ____ may be defined in coplanar and non-coplanar arrangements.

Arc therapy, arcs

 overlapping multiple intensity modulated fields, high radiation doses are delivered to targets that are irregularly shaped or close to critical structures describes what?

intensity-modulated radiation therapy 

intensity-modulated radiation therapy description

Rather than using a uniform beam, IMRT breaks the radiation down into small "beamlets" and varies the intensity (strength) of each beam

A treatment technique that involves the use of dynamic multi leaf collimation and gantry arcing 

Volumetric-modulated arc therapy 

These techniques treat small targets with many intersecting beams creating concentrated dose areas with very sharp dose falloff.  

Stereotactic radiation therapy (gamma knife)

two types of Stereotactic radiation therapy 

Stereotactic body radiation therapy (SBRT) or stereotactic ablative radiation (SABR) use stereotactic techniques to treat small well-defined lesions outside of the cranial, head and neck regions. Highly precise localization and treatment plans deliver intense radiation doses