Treatment Techniques (Definitions and Terminology)

Towards the head

superior

away from the head

inferior

towards to the front

anterior

towards the back

posterior

nearer to the front

medial

farther from the midline

lateral

nearer to the point of origin/attachment

proximal

farther from the point of origin/attachment

distal

on/near the surface

superficial

away from the surface

deep

• Perpendicular to the sagittal plane

• Divides the body into anterior and posterior sections

Coronal

• Perpendicular to the midsagittal, parasagittal, and coronal planes

• Divides the body into superior or inferior parts

Transverse

Divides the body into right and left parts

• sagittal plane

  • Midsagittal (Median Sagittal) - Plane divides the body into equal right and left halves

  • Parasagittal Plane - Divides the body into unequal right and left portions (parallel to the midsagittal plane)

• Prevalence: ~5% of the population.

• Build: Short, wide trunk; large body weight; small pelvic cavity.

• Stomach position: High, wide, and horizontal.

• Other features: Heavy skeletal framework; large alimentary tract.

• Clinical note: May require cross-positioning in chest X-rays to capture the entire chest

Hypersthenic

• Prevalence: ~35% of the population.

• Build: Below average; more slender and elongated.

• Stomach position: Slightly lower J-shaped; more medial placement.

• Other features: Abdominal cavity size between sthenic and asthenic; similar organ positioning to sthenic but slightly lower

Hyposthenic

• Prevalence: ~50% of the population (most common).

• Build: Average physique; heavy skeletal structure; well-developed musculature.

• Stomach position: High, J-shaped, in the left upper quadrant.

• Other features: Moderate thorax length and depth; moderate lung and heart size.

• Clinical note: Serves as the standard reference for normal anatomical measurements

Sthenic

• Prevalence: ~10% of the population.

• Build: Very slender; light body weight; long abdominal cavity.

• Stomach position: Low and elongated; close to the vertebral column.

• Other features: Light skeletal framework; pelvis with greater capacity.

• Clinical note: Heart may appear “hanging” in the thorax; requires special imaging positioning

Asthenic

• A medical specialty that uses ionizing radiation to treat cancer and some benign diseases

• Standard equipment – Linear accelerator

Radiation Therapy

• Process of determining the patient treatment position, the volume to be treated and the normal structures in or surrounding that volume

• Standard equipment- CT scanner

Simulation (treatment planning procedure)

1

Drive stand

2

Gantry

3

Patient support assembly (treatment couch)

PSA

patient support assembly, table or couch

TT

table top distance: the distance from the table top to the isocenter

1

collimator

2

gantry (360 rotation)

3

table

hand pendant

table controls

• Point of intersection of the three axes of rotation – (gantry, collimator, couch) of the treatment unit

Isocenter

• The treatment unit isocenter is static

• It is a set distance of 100 cm from the treatment source

treatment approach where the treatment unit’s isocenter is placed at a reference point within the patient, typically within or near the target volume

Isocentric Treatment

The physical size set of the treatment field at the isocenter

field size

• Defined at the machine’s isocenter (a distance of 100 cm from source)

• Represented by W x L

• Accomplished by the jaws inside the collimator

  • X and Y are the upper and lower jaws

  • Asymmetric jaws with modern technology •

    • Jaw moves independently

The red arrow is pointing to the ______ of the beam.

central axis

• device mounted on or near the collimator head that projects a scale onto the patient’s skin

• number projected at the central axis is the distance from the source to the skin surface (SSD*)

ODI – Optical Distance Indicator

• ____ project via a red or green light used in the simulation and treatment process

• ____ project in the transverse, sagittal and coronal planes

• ____ assist in positioning by providing external reference points in relation to the position of the isocenter

Lasers

Patient/Table/Source/Distance Relationship

The redlines on this diagram demonstrate the isocenter of this patient.

the distance beneath the skin surface where the prescribed dose will be delivered

depth

measure of patient’s thickness from the point of beam entry to beam exit

Patient Separation

the distance from the source or target of the treatment machine to the surface of the patient (skin)

Source-Skin Distance (SSD)

• Also TSD (target-skin distance)

• Measured with the ODI

• Where the field size is defined on the surface

  • The field size set on the collimator is the same as measured on the skin surface of the patient

the distance from the source of photons to the isocenter of the treatment machine

Source-Axis Distance (SAD)

• Also, target-axis distance

• The SAD for modern linear accelerators is 100cm

• the field size is defined is inside the patient at the isocenter distance

control console

control console

Unit of output measure used for linear accelerators

Monitor Units (MU)

• MU is the length of time a unit is physically on to deliver a prescribed dose. The MU is the treatment “time” for a linear accelerator.

• Linear accelerators are calibrated so that 1 MU delivers 1cGy for a standard source to calibration point

• Also known as output

  • The amount of radiation exposure produced by a treatment machine or source specified at a reference field size and distance

  • Changing the field size, distance or attenuating medium will change the ____.

  • ____ increases with increased field size. (when there is an increase in field size, the scatter is increased which adds to the output.)

Dose Rate (cGy/MU)

• Spreading out of the beam of radiation.

• More tissue is exposed as the beam exits the patient than at the anterior skin surface.

divergence

The dose prescribed by the physician at a particular depth within the patient that will provide adequate coverage of the tumor.

Tumor Dose (TD)

• Dose delivered to Dmax depth through a single treatment field

• Also known as applied dose, or Dmax dose

Given Dose (GD)

• The depth of maximum buildup, in which 100% of the dose is deposited beneath the skin.

• The depth at with electronic equilibrium occurs for photon beams

• The depth of maximum absorbed dose and ionization in a single treatment field for photons.

Dmax depth

• The ratio expressed as a percentage, of the absorbed dose at a given depth to the absorbed dose at a fixed reference depth, usually Dmax.

• Percent Depth Dose (PDD)

• PDD= Absorbed Dose at Depth / Absorbed Dose at Dmax

documentation of treatment portals through radiographic images or electronic portal images

Portal verification (port film, PF)

• Planar or CT images confirming treatment setup

• Completes treatment record and verification image communication between therapist and Rad Onc

• Documents treatment localization reproduction

  • Images are acquired with the patient in the treatment position and compared with reference images from the treatment plan and initial simulation.

Verification Imaging

• Blocked field size

• The equivalent rectangular field dimensions of the open or treated area within the collimator field dimensions.

• It is the actual area treated

Effective Field Size

• Images reconstructed from CT data that represent the patient’s anatomy and defined volumes from the perspective of the treatment beam.

  • Viewing the patient anatomy from the perspective of the treatment field

  • Helps to ensure the orientation of the patient and the treatment machine are correct

    • Useful in identifying best gantry, collimator, couch angles

    • Verifies geometric coverage of target volume

    • Shielding and MLC design

Beam eye view – BEV

area of known and presumed tumors

Target Volume

process by which does delivery is optimized for a given patient and clinical situation

Treatment planning

a graph that evaluates and displays how much dose is delivered to a target or surrounding critical structures

Dose Volume Histogram (DVH)

• two radiation fields configured so that the beam edges lie on the same geometric plane

  • Used to align field edges so the dose matches more evenly at the junction/margin

  • The central rays are not necessarily parallel opposed

Coplanar

fields arranged on different planes, often requiring couch or gantry angle changes

Non-coplanar

• When radiation beams lie in the same plane, this is ____.

• When one beam lies in a plane and another beam passes through that same plane, this is ____.

• coplanar

• noncoplanar

• Coplanar and Non-coplanar

• *VMAT: Volumetric Modulated Arc Therapy

the measure of the angle between the central rays of 2 intersecting treatment beams

Hinge angle

• two images taken at 90 degrees apart

  • used for setup verification and treatment planning

  • used to define the location and relationship of various anatomic structures relative to the fields isocenter

Orthogonal Films

• Dose to any tumor or mass is limited by its surrounding structures and tissues.

• Tolerance doses were established for normal tissues in terms of total dose delivered by a standard fractionation schedule that caused minimal (5%) or maximal (50%) complication rate within 5 years

• NTTD is affected by 2 factors:

  • Volume irradiated

    • Organs can tolerate more dose if the volume of the organ being irradiated is small

    • As volume of organ increases the tolerance dose for the whole organ decreases

  • Fractionation

Normal tissue tolerance doses (NTTD)

• ____ is the dose that would likely cause 5% of an exposed population to produce an adverse late effect in 5 years following exposure.

  • Relates to the minimum dose it would take to cause injury in 5% of patients within 5 years

  • OR

  • Total dose delivered by a normal standard fractionation that causes (5%) minimal complication rate within 5 years = ____

TD 5/5

• ____ is the dose that would likely cause 50% of an exposed population to produce an adverse late effect in 5 years following exposure.

  • relates to the maximum dose it would take to cause stated injury in 50% of patients within 5 years

  • OR

  • Total dose delivered by a normal standard fractionation that causes (50%) maximum complication rate within 5 years = ____

TD 50/5

• The total dose for Radiation treatments is divided into daily fractions over an extended period of time

• (individual treatment dose)

Fractionation

• time period during which the total treatment dose will be given (number of treatments or days)

  • Type of tumor and the tolerance of normal tissue in the treatment field determine the total dose, size, number of fractions, and treatment duration (protraction)

  • As the daily fraction (daily dose) increases

    • Cell killing increases

    • The cells ability to repair sublethal damage decreases • results in a decrease in the radiation tolerance of the normal tissues.

Protraction

• Common Abbreviations

  • TSD/SSD

  • TID/SID

  • TOD

• target/source to skin distance

• target/source to image receptor distance

• target to object distance

Simulation - review of some terms

Directional Acronyms

• AP

• PA

• RT

• LT

• POP

• Tangential (tangents, “tangs”)

• anterior-posterior

  • CA is directed from anterior to posterior

• posterior-anterior

  • CA is directed from posterior to anterior

• Right

• Left

• parallel opposed – two treatment fields planned 180 degrees apart

  • can enter the patient from any two directions relative to the patient (i.e., rt/lt laterals, AP/PA, and anterior and posterior obliques)

• opposing fields which flash off the surface of the patient

Directional Acronyms

• LAO

• LPO

• RAO

• RPO

• left anterior oblique – the central axis is directed from the left anterior aspect of the patient

• left posterior oblique – the central axis is directed from the left posterior aspect of the patient

• right anterior oblique – the central axis is directed from the right anterior aspect of the patient

• right posterior oblique – the central axis is directed from the right posterior aspect of the patient

AP/PA

LAO/RPO

RT/LT Laterals

LAO/RPO

AP, RPO/LPO

____ is a line perpendicular to the cross-section of the simulation or treatment field. It is the only imaginary line emanating from the source (focal spot) of radiation that is not divergent.

CA (CAX) - Central Axis

____ is a measurement used for treatment planning purposes to determine the thickness of a body part from entrance point to exit point, often measured along the CA.

IFD - Intrafield distance (also called separation)

Any process used to capture the X-ray, magnetic resonance image (MRI), or sonographic information, including film, electronic, or digitally reconstructed radiograph (DRR).

Image

Point in space where radiation beams intersect from any of the 360-degree gantry angles. It is similar to the spokes of a bicycle wheel intersecting at the axle

Introcenter

____ is the distance from the source of radiation to the axis of the radiation beam or isocenter (also referred to as TAD [target-axis distance]).

SAD - Source-axis distance

____ is the distance from the target of radiation to the imager

TID - Target imager (receptor) distance

____ is the distance from the source of radiation to the skin surface of the patient (also referred to as TSD [target-source distance])

SSD - Source skin distance

Geometric point or area where the radiation beam emerges and fans out or diverges as it moves farther from the source, target, or focal spot.

Virtual/focal spot

Common abbreviations

• DRR

• MLC

• V & R

• Digitally reconstructed radiograph

• Multileaf collimator

• Verify and Record system