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