High yield exam facts Flashcards
rules for estimating electron PDD characteristics:
R50 = Energy/2.33
1) Surface dose = 73+Energy
e. g 6MeV SD =79%
2) “4,3,2 divide rule”: Dmax = Dose/4, R90 = D/3, R10 = Dose/2.
E.g 6/4 = 1.5cm = Dmax, 6/3 = 2cm = D90, 6/2 =3cm = R10 (therefor D50 = 2.5cm)
alpha/beta ratios for acute, and late responding tissues:
Define standard fractionation
Acute = 10Gy
Late = 3Gy
(Don’t forget has units of Gy)
Standard fractionation: 1.8-2Gy/fraction, daily fractions, five days a week.
When does the brachiocephalic vein become the subclavian?
In the root of the neck, the internal jugular (IJV) and subclavian veins unite to form the brachiocephalic veins posterior to the medial ends of the clavicles.
Define monitor unit
1) SSD
MU = dose (cGy)/
CalibrationFactor(PDD.WF.OF)
2) SAD
MU = dose (cGy)/
CalibrationFactor(TPR.WF.OF)
SSD - The source surface distance (if different to reference conditions)
OF - The field size (usually referred to as the output factor or total scatter factor)
PDD - The percent depth dose of the point in question
WF (wedge factor) The presence of any beam modifying devices in the beam (such as a wedge)
CF - The calibration factor (only important if 1 MU is not equal to 1 cGy under reference conditions)
Define Housfeild unit
u = linear attenuation ux = linear attenuation of beam
HU = ((ux - uwater)/(uwater- uair)) X 1000
Define physical half life
The time it takes for 1/2 the atoms of a radioactive material to decay to half their number.
Defined by a decay constant, such that Thalf = ln(2)/decayconstant
Where
decay constant it the basic term in a decaying exponential.
Define effective half life
The time taken for a concentration of a radioactive to material to be reduced by half in a body, either by decay or clearance.
Teff = ln(2)/Effective decay constant
where
Effective decay constant is the sum of physical and biological decay constants
Define radioactive equilibrium:
The state where a radioactive nuclide is decaying at the same rate it is being produced. The key condition is that the parent nuclide has a longer half-life than its descendants.
decayconstan1 x NumberAtoms 1 = decayconstant2 x NumberAtoms 2
Types of radioactive equilibrium (and examples):
1) Half-life of parent nucleus is longer than a half-life of the daughter nucleus, but the concentration of parent nuclei significantly decreases in time. In this case, the parent and daughter nuclide decay at essentially the same rate, but both concentrations of nuclides decreases as the concentration of parent nuclei decreases. Contrary to secular equilibrium, the half-life of the daughter nuclei is not negligible compared to parent’s half-life. E.g the cow: Moly 89 (67hrs) -> Technicium 99 (6hrs) 2) Secular equilibrium: Where parent half life is many orders of magnitude greater than daughter, and concentration of parent essentially doesn't change. radium 226 (1600 years) -> Radon 222 (3.6 days)
What defines the inferior border of the superior mediastinum?
Some critical shit that happens there
Plane of Ludwig/Transthoracic plane/sternal plane
Plane from angle of Louis (sternal angle) to inferior border endplate T4.
Bifurcation of pulmonary trunk
Bifurcation of trachea
Factors that effect the therapeutic ratio can be broken into:
1) Physical: Fractionation pattern, radiation quality, total dose, treatment time, temperature
2) Biological: Tumour factors (radiosenitivity, size, location), host factors, tissue factors (e.g. organisation)
3) Chemical: Concurrent therapies, oxygenation, protectors, sensitizers
4) Technical: system accuracy, conformity, geographic miss, presence of hotspots.
Steps in angiogenesis:
1) Angiogenic switch in favour of angiogenesis:
pro-angio>anti-angio
E.g pro: VEGF, TNF alpha, TGF beta
E.g anti: Angiostatin, endostatin, interferon
2) Endothelial cell proliferation
3) Neoangiogenesis
4) Resolution/maturation phase - often missing in tumour angiogenesis leading to shitty leaky, collapsing vessels.
Define effective energy:
The theoretical mono energetic beam that has the same HVL as a polyenergetic beam under study. Practically difficult due to beam hardening requiring progressively greater HVLs…
1mm Al filters out energies up to? This is roughly equivalent to?
filters up to 10Kev
Roughly equivalent to inherent filtration (i.e your inherent filtration curve should start at 10Kev).
G2/M check point proteins
Cyclin B - CDK1
(Cyclin B promoted by Cyclin A - CDK1)
CHK1/CHK2 (ATR/ATM) - p53 - p21
CDC25a
Compare pulmonary arteries to veins
What do the main pulmonary veins drain?
Pulmonary arteries follow bronchial tree to alveoli.
Pulmonary veins follow intersegmental septa and exit hilum inferior to arteries.
Right:
Superior drains upper and middle lobe
Inferior drains LL
Left:
Superior drains UL + LIngular
Inferior drains LL
Lymphatic drainage of the breast should always been with:
Inferior border of breast? and ribs cover
After the apical nodes what happens?
How much of the lymphatic drainage of the breast is through the axillary nodes
With obstruction of usual lymphatics what can happen?
“Deep and superficial (Sappey’s) plexi merge”
Inframammary fold, breast covers ribs 2-6
Subclavian trunk -> right or left thoracic ducts
Axillary nodes drain 75%
Lymphatics may cross to contralateral side through superficial (dermal channel), deep (internal mammmary interconnections) or to the retro-pectoral nodes.
Roots of:
Sacral plexus
Sciatic nerve
Pudendal nerve
Sacral plexus
L4-S4
Sciatic nerve
L4-S3
Pudendal nerve
S2-S4
Roots of the sacral plexus:
Divided into what rami?
L4-S4.
Anterior Rami (s1-s4): Pelvic splanchnic, pudendal, perineal (S4) Anterior division of anterior rami (L4, S3) - gives off tibial sciatic branch. Posterior rami (L4, s2) - Given of common peroneal sciatic branch
Methods/systems/equipment to avoid or detect dose delivery errors?
● Record and Verify System
● Select and Confirm
● Interlocks
● Imaging
What is the Record and Verify System?
What does it include?
Record and Verify System
○ Ensures that the planned treatment is delivered in a similar manner every day, consistent with plan, and records in real time. Measured variables are compared against tolerance and system alerts if outside.
○ Includes daily measurements of: ■ MU (recorded in real time) ■ beam energy ■ beam mode (photons/electrons) ■ jaw positions ■ collimator, gantry and couch angles ■ wedging ■ SSD
What is the Select and Confirm System?
What does it include?
○ Ensures correct treatment parameters
○ When a setting is selected, mechanical changes are checked to have occurred before treatment continues.
○ System also checks that the field correlates with the mechanical positions of the field, collim
What 2 types of error impact treatment accuracy?
● Systematic errors
○ constantly inconsistent error that is reproducible
○ inherent accuracy of treatment or positioning
○ eg. errors in patient setup, incorrect collimation, treatment plan transcription errors, incorrect calibration of measurement tools
● Random errors
○ errors due to unpredictable variations in measurements, fluctuate around a mean value.
○ Can be minimized with more precise measurements and improved patient immobilization
○ eg. patient movement, organ motion, inconsistent interpretation of skin marks and positioning.
Radiation worker dose limit:
Chest XR dose
Abdo CT dose
20msv/year averaged over 5 years, not more than 30mSv in any one year
CXR 0.02 - 0.1
CT Abdo: 10-20 mSv (depending on study - e.g tripple phase)
The primary cellular target of ionising radiation is DNA.
i. List the four (4) main types of DNA lesions caused by therapeutic ionising radiation.
1) ds-DNA break
2) ss - DNA break
3) Base modifications
4) Interstrand crosslinks
Describe the processes of non-homologous end joining (NHEJ)
1) Detection: DSBs detected by Ku70 and Ku80 proteins which bind to site (also protect ends)
2) Recruit: DNA-PKcs recruited - autophosphorylates and phosphorylates other proteins.
3) Artemis (protein complex) recruited to DNA break, forms complex with DNA-PKcs and is activated by phosphorylation.
4) Processing: Artemis endonuclease activity processes the DNA ends ready for ligation.
If non-blunt end of DNA i.e. a 3’ or 5’ overhang, then the absent DNA can be generated accurately by polymerases.
5) DNA ends ligated
Describe the processes of homologous end joining
Homologous Recombination uses sister DNA with the same sequence as a template for repair. After activation as above:
1) Single stranded filaments made around DSB
2) Filaments coated with RPA
3) RAD51 displaces RPA and SEARCHES and INVADES sister chromatid
4) HELICASES UNWIND DNA and hold open SEPARATION FORK and polymerases SYNTHESISE 5’-3’ along separation fork.
5) Finally crossover points are CUT by RESOLVASES, and ligated
Detection→Recruitment/activation→Processing→Ligation
Why are lower photon energies used in lung plans?
Remember the graph of 6Mv
- pre interface less scatter, but then due to less attenuation of beam, dose is higher. Higher dose causes increased range scattered electron = wider penumbra.
Therefore:
1) Energies >6Mv will cause increased dose to lung due increased electron range
2) Higher energy/less attenuated beams will have a build up region within the more solid tumour leading to less even coverage of the tumour.
Difference between LET and stopping power
While mean stopping power refers to the energy lost by the particle beam traversing the surrounding media, linear energy transfer (LET) refers to the energy absorbed by the media per unit of distance travelled by the ionizing radiation.
LET does not include radiative energy (i.e it leaves the area - um).
Why does a 6Mv beam deposit less dose in a bone inhomegeniety?
Why is the beam attenuated after?
Less electrons/gram = less compton attenuation
But more attenuation of the primary beam (electrons per cm) leads to decreased dose behind inhomogeneity.
Job of each HPV oncogene:
E5 = EGF ,E6 = p53, E7 = Rb
E5
Activates EGF signalling pathway (i.e RAS-Raf-Mek-Erk, and PI3K-AKT-mTOR) ->Cell growth and proliferation
E6
Binds p53 induces its degradation
E7
Binds Rb releasing E2F: Cyclin E increases, Cylcin A-CDK2 stimulated, cell goes into S Phase.
Inactivates CIP/KIP (p21, p27)
Name some tumour suppressor
TP53
Rb1
PTEN
INK4a locus
