Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
80 Cards in this Set
- Front
- Back
- 3rd side (hint)
What is the transmission formula? |
HVL = 1/2ⁿ
|
|
|
What is the field size on the skin (surface) formula?
|
SAD - depth/ SAD
answer x field size at SAD |
|
|
Transmission formula = attenuation
|
It = Iₒ e- 0.693 x thickness/ HVL
HINT use 100 for Iₒ if original intensity is not given |
|
|
TVL formula
|
TVL = 3.32 x HVL
|
|
|
Linear coefficient
|
ɥ = 0.693 / HVL cm-1
|
|
|
Given dose (or dmax dose)
|
(tumor dose/Pdd) X 100
|
|
|
TPC
|
(273.2 + Cᵒ/ 295.2)(760/P)
760 is in mmgh use 1013.2 mbar |
|
|
Celsius conversion to farenheit
|
C = 5/9 (F - 32)
|
|
|
Mayneord Factor (Big F)
|
(New + dmax/ Old SSD + dmax) X (Old SSD + depth/ New SSd + depth)
multiply the answer by the original pdd |
|
|
Decay formula
|
A = Aₒ e - 0.693 x time /T 1/2
|
|
|
Penumbra
|
GP = s(SSD + depth -SDD)/SDD
If no given depth use 0 source size must be converted to cm by s/10mm |
|
|
Magnification
|
Img distance/ Object distance
or Img size/ Object size |
|
|
Exposure to dose conversion
|
Exposure x dose = rads
|
|
|
Dose to exposure conversion
|
Dose / exposure = R
|
|
|
Dmax or Given dose
|
tumor dose / pdd
|
|
|
Inverse Square
|
I₁D ₁²= I₂D₂²
Old /New |
|
|
Scatter to Air Ratio = SAR
|
Scattered dose at given point in phantom / dose in free space at same point
Independent of SSD Dependant on Energy, depth, field size |
|
|
Equivalnt Square = EQSQ
|
4A / 2P
or 4 (L X W) / 2 (L + W) |
|
|
Wedge factor
|
dose with wedge / dose without the wedge
measured at 10cm |
|
|
RX given dose or dose to a point
|
RX dose @ depth / Pdd @ RX dose
X Pdd @ depth of interest |
|
|
Equivalent Radius = EQRA
|
4A / square root of pi *P
4 (l x w) / square root of pi * 2(l + w) |
|
|
# e- per gram formula
|
NA x Z / A
OR 6.02205 x Z# / A |
|
|
TAR
|
Dose in the phantom / dose in air at the same point
|
|
|
Pdd
|
Depth / dmax X 100
|
|
|
Electron density formula
|
Pe = Pm Na Z /A
|
|
|
Avogados number (number of atoms)
|
Na = 6.02205 X 10²³ atoms
|
|
|
Atoms per gram formula
|
NA / A
OR 6.02205 10^23 / A |
|
|
As Pdd increases
|
E↑ Field Size↑ depth↓ SSD↑
|
|
|
As TAR increases
|
E↑ Field Size↑ depth↓
Independent of SSD or SAD |
|
|
As TMR increases
|
E↑ Field Size↑ depth↓
Independent of SSD or SAD |
|
|
Wedge factor is dependant on
|
Energy, Field size, depth
|
|
|
GTV
CTV PTV |
Gross tumor volume, clinical tumor volume, planning target volume
|
|
|
Which one of these is most important .
GTV CTV PTV |
PTV
|
|
|
Back scatter factor = BSF
|
dose at dmax / dose in air
at the same point |
|
|
OD = optical density
|
log lₒ / lᵻ
or log without film / with film divide first then log |
|
|
GAP
|
(L₁x d /2SSD₁) + (L₂x d/2SSD₂)
|
|
|
Collimator formula
|
(1/2 L₁x 1/SSD) -1 tan
OR (L/2/SSD) -1 tan |
|
|
Couch formula
|
(1/2 L₁x 1/SAD) -1 tan
OR FIELD LENGTH/2/SAD) -1 TAN |
|
|
TPR = tissue phantom ratio
|
dose in tissue at a point / dose in phantom at referenced depth
IF that depth is dmax then it is TMR |
|
|
Atomic # Z what is the division between #protons and e- and neutrons
|
number of protons + number of e- = Z
|
|
|
Atomic mass A
|
number of protons + # neutrons = A atomic mass
|
|
|
What is 2n²?
|
n is the quantum number
|
|
|
MU formula
|
TD/Junk
|
|
|
T or F
BSF and TAR @dmax are the same? |
True
|
|
|
Calculate the MU of a 6 MV e- beam with a 15 x 15 cm cone. RX dose is 200 cGy at 95 % isodose line. The output of a 15 x 15 cm cone is 1.042.
|
MU =TD/Junk
200/ 1.042 x 0.95 = 202MU |
|
|
Calculate the MU of a 6 MV e- beam with a 15 x 15 cm cone. RX dose is 200 cGy at 95 % isodose line. The output of a 15 x 15 cm cone is 1.042. If there is a 1cm bolus what is MU?
|
MU =TD/Junk
200/ 1.042 x 0.95 x (100/99)² = 198 MU |
|
|
Rule of thumb
How far will your energy travel? |
E/2
E/3 = 80% E/4 = 90% |
|
|
T or F
If a lesion is on the skin you will have to use dmax thickness of bolus of that Energy? |
True
4 MV use 1cm bolus 6 MV use 1.5 cm bolus |
|
|
Compton and photoelectric interactions are produced by what machine energy ranges
|
Compton by Mega (bone- high Z)
Photoelectric by Orthovolt |
|
|
T or F you can use MLCs with Island blocks?
|
False you cannot
|
|
|
Calculate the gap of 2 adjacent fields which are
10 x 10 cm 100 SSD 15 x15 cm 100 SSD The matchline depth should be 7 cm |
gap = L₁*d/2SSD + L₂*d/2SSD
10*7/200 + 15*7/200 = |
|
|
%dd for a 10 x 10 field at 10cm with 80cm SSd (dmax at 1cm) using a 4 MV photon is 62.2. Find the %dd for the same field size and depth at 100 cm
|
(NEW SSD +dmax/OLD SSD +dmax)²*(OLD SSD + depth/ NEW SSD +depth)² x original pdd
(100 +1cm/80+1cm)² *(80+10/100+10)² x 62.2 = 64.73 % |
|
|
What is the collimator angle if the spine field is 18 cm long at 80 SSD?
|
(1/2 L* 1/ssd) arc tan -1
(18/2 * 1/80 )*tan -1 = 6.4 |
|
|
What is the couch angle if the brain field is 16 cm in length at 100 SAD?
|
(1/2 L* 1/sad) arc tan -1
(16/2 * 1/100) *tan-1 = 4.57 |
|
|
T or F
For orthovoltage (E up to 400 kvp) and lower E xrays the dmax is on the skin and always 100%? |
True because dmax is always on the skin
|
|
|
Calculate the Hvl of a material if the thickness to produce 60% transmission is 7cm.
|
It = I₀ e- 0.693*t / HVL
60 = 100 e- 0.693*7 / HVL 60/100 = e- 4.851 / HVL ln .6 = -4.851/ HVL -0.51082 = -4.851/HVL HVL = -4.851 / -.51082 HVL = 9.49 |
|
|
During a 2.5 minute fluoroscopy exam a tech was exposed to 250 mR/hr. What is the exposure?
|
Exposure = Rate x Time
250 mR/hr * 2.5 min/ 60 min 250 mR * .04166 = 10.4 mR |
|
|
What is Tar at 5 cm depth if dose at 5cm is 180 cGy and dose in freespace is 210 cGy?
|
180cGy / 210 cGy = .857 or .86
|
|
|
Definition
The thickness of material required to reduce the intensity of the beam to 1/2 its original value |
HVL
|
|
|
Definition
Thickness of material required to reduce the intensity of the beam to 1/10th its original value |
TVL
|
|
|
Hinge Angle
|
180/2 - wedge angle
HELP ME LIZ I THINK I AM LOSING IT |
|
|
Wedge Angle
|
90- hinge angle / 2
|
|
|
Tray factor
|
Dose with tray / dose without the tray
|
|
|
Exposure
|
exposure rate X time
|
|
|
Radium Equivalent - brachy
|
『A/『ra
OR source * activity / Ra source |
|
|
Exposue at distance - brachy
|
『A /d²
|
|
|
Exposure time - brachy
|
『 A t/『ra
|
|
|
Mghr -- perm implant
|
RaEq *1.44 * T1/2 *24 hrs
|
|
|
Mghr -- temp implant
|
RaEq * T1/2 * 24 hrs
|
|
|
Field weighting
|
When beams are weight equally each field receives the same amount of dose --180/4 = 45 cGy per field
As weight is increased the hot spot moves toward the surface of that beam AP/PA field weighted 3:1 with a dose of 200 200/4 = 50 3 * 50 = 150 1 * 50 = 50 |
|
|
What is image size of a block if magnification is 3.2 cm and object size is 1.25?
|
mag = img size/obj size
3.2cm = image size/ 1.25 3.2 * 1.25 = 4 |
|
|
What is the depth of 50% of a 10 MeV e- energy?
|
E/2 = 10/2 = 5
???? |
|
|
The atom neutral provided the # of e- and the # of protons is the same. If the atom has more e-, is the atom neg or positive?
more protons? more neutrons? WHY??? |
more e- = neg atom b/cuz e- are neg
more protons = positive atom b/cuz protons are positive more neutrons nothing, b/cuz nuetrons are nuetral |
|
|
AMU
|
atomic mass unit
atomic weight is measured in atomic mass unit |
|
|
Isotopes (ZA)
|
Nuclear with the same # of protons and different # of neutrons
Same Z but different A 12 13 C C 6 6 same chemical reaction because of same Z (6) |
q |
|
Isobar (AZ)
|
have the same atomic weight A different Z
do not have same chemical reaction |
|
|
Isotone (N)
|
Isotone have the same # neutrons different Z and different A
|
|
|
Annealing
|
heating to remove radiation from ionization chambers
|
|
|
How is absolute dose measured?
|
Ion chambers and Fricke dosimetry.
absolite dose means 1 rad is 1 rad |
|
|
Who calibrates ion chambers and how often
|
Calibrated by ADCL or NIST
Survey meters calibrated once a year |
|