Section 1 Part 2: MV intro and Cobalt

Megavoltage (1 MV or greater)

Megavoltage aka

supervoltage

Supervoltage

1. aka Megavoltage

2. a series of machines in the 1920s-1940s that utilized energies between orthovoltage and megavoltage—> later morphed into linear accelerators (fyi: van de graaff generators, betatrons)

Who paved the way for supervoltage (MV) units? In what year?

Coolidge (inventor of Coolidge tube)

1930s

supervoltage (MV) units aka

cascading tubes

The first supervoltage machine that actually got to 1 MV was used in (location)?

London

In America, _1__(company) made a supervoltage machine unit installed at _2__(hospital) in _3_(location)_4_(year)

1. GE

2. Mercy Hospital

3. Chicago

4. 1933

Linear accelerator was invented by _1__ (person) in ___2__ (year).

William Hanson

mid-1940s

(hint on year: the Varians were developing it for WW2 use)

Hanson’s research was based on work by ____

Russell and Sigurd Varian

Who developed the linear accelerator for medical use?

Russel and Sigurd Varian

Types of MV machines

Tiny green cyclops bites

1. Co60

2. linac

3. microtron

4. Van de Graaff

5. Cyclotron

6. Betatron

Advantages of MV machines

1. skin sparing effect: Dmax below skin surface

2. increased PDD (tx tumors with fewer side effects)

3. sharp edge gradient

4. Compton’s Scatter as primary interaction

Super Powers Eliminate Cancer (SPEC)

Dmax aka:

1. 100% depth

2. Given dose

3. Electronic equilibrium (equilibrium depth)

Dmax depth is primarily a function of ___, meaning:

beam energy

higher Energy = deeper Dmax

PDD

Percent depth dose: the % of dose at a certain depth

sharp edge gradient meaning

INSERT PIC. Side scatter from KV machines causes the isodose curves to bulge outwards, resulting in a higher dose outside the edge of the field compared to linacs.

Historical development of Co60

1951: first medical use of cobalt machine

1st practical unit to provide skin sparing

most common tx machine 50s and 60s

Cobalt machine is regulated by?

narcs!!!

NRC: Nuclear Regulatory Commission

Dmax Depth of Cobalt Machine

0.5 cm

HVL used for cobalt machines:

1.2 cm Pb (lead)

Cody is 12 he likes PB sandwich

For registry questions:

1. Co60 and 137Cs are referred to as:

2. and linacs are referred to as:

1. teletherapy

2. megavoltage therapy

Type of radiation for Cobalt machines:

Gamma rays

gamma ray symbols

Γ, γ

Energies used in cobalt

1.17 MV & 1.33 MV

Average energy cobalt is calculated to

1.25 MV

half life of cobalt:

5.26 years

cobalt decays at: (rate)

1.1% per month

term. decay scheme

def. a graph of a radioactive element’s decay pattern

isocentrically mounted equipment was first proposed in ___

1950

term. isocentrically mounted equipment

equipment that rotates in a full circle around isocenter ( a fixed reference point in space)

SAD

Source to Axis Distance

aka source to isocenter distance

SSD Technique

SSD = SAD

Isocentric (SAD) technique

SSD /= SAD

Co60 tx is calculated and preformed using a __ technique

SSD

SSD for cobalt tx

80 cm

True or False: Isocentric (SAD) Technique is the same as isocentrically mounted machine

False: Isocentric technique means: SSD = SAD

while isocentrically mounted machine means: machine spins in 360 degrees around isocenter.

Isocentrically mounted machine could use either/both SSD and SAD techniques

What is the problem with SSD technique?

for 4 field technique you have to adjust table to make isocenter 80 from each field INSERT PIC

True or False: Early cobalt machines were isocentrically mounted machines

False: they were non-isocentric

Swiveling head, NOT a rotational one

1 Ci =

3.7 × 10 ^10 dps