Intro to RT: SSD/SAD Treatment Techniques

SSD

Source to skin difference

SSD Treatment Technique

when using this type of treatment the SSD is always 100cm (MAYO 110cm for safety)

therefore, with an SSD of 100cm the field size is accurately represented on the patient's skin surface

ie. you could measure the 10 by 10cm field on the patient's abdomen.

In order to treat using this method, an AP and PA (single parallel opposed) fields are utilized by rotating the couch 180 degrees

Typically used for bone mets of palliative treatment

What is an advantage of the SSD Treatment technique?

Allows for a larger field size

Extended Distance

greater than 100cm may be used to get the desired field size

distances vary - typically 125cm

ie. treating whole abdominal field

Linac - 100cm SSD

Cobalt 60 - 80cm SSD

40x40 is the largest possible F.S.

Electron Cone treatment has an SSD of

100cm

Posterior spine - Static (non-IMRT)

uses the SSD treatment technique

rarely done anymore

SAD

Source to Axis Distance

SAD Treatment Technique

"Isocener technique" - we see this daily

Machine rotates about a fixed point

field size defined as isocenter

Patient does NOT need to move

SSD = less than 100cm

Advantage of SAD technique

allows more complex and sophisticated treatment - 3 point system

ie. 3D conformal, obliques, arcs

standard treatment technique at most institutions

What is the purpose of Topographical Landmarks?

to assist in approximating field borders or scanning parameters as closely as possible before imaging or scanning.

knowledge of landmarks will assist in writing set up instructions and describing isocenter or tattoo locations

Nasion

root of nose

Canthus

corner of the eye

fleshy vs. bony

Mastoid Tip

level of C1

Palpated during whole brain set ups

Orbital Ridge

Inf & Sup

whole brain eye block placement

External Occipital Protuberance

inon

Tragus

flap of cartilage located anterior/medial to EAM

Thyroid Notch

superior-most point of the thyroid cartilage of the Larynx

Forms a 'V'

Used to locate vocal cords

Suprasternal Notch

U-shaped depression just above the sternum, between the clavicles

T2-T3

Also called: jugular notch, SSN, Manubrial Notch

Sternal Angle

Bony prominence at the junction of manubrium and body of the sternum

T4-T5

Level of Carina

Also called: Angle of Louis

Xiphoid Tip

T10

Iliac Crest

superior ridge of the ilium

L4

Anterior Superior Iliac Spine

ASIS

L5-S1

bifurcation of common iliac vessels

Inferior Angle of Scapula

T7

Pubic Symphysis

below the spine (near level of coccyx)

Cisterna Chyli

L1-L2

Lymphatic drainage vessel from lower limbs and pelvic region