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)
or 2,3,4,5 times rule
E.g. Max 2x6 = 12mm
R90 3x6 = 18mm
R50 4x6 = 24mm
RP 5x6 = 30mm
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
A monitor unit is a measurement of ionisation occurring in a treatment beam within the treatment head. One monitor unit is typically equal to a specific dose of radiation, at a specific depth in a water phantom, for a beam of a particular energy, with a particular field size and at a certain distance from the target.
Monitor units are used to measure the output of the machine to deliver accurate dose.
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
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).
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)
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.
What is the lymphatic drainage of:
1) Body of pancreas
2) Tail of pancreas
Pancreosplenic nodes - follow splenic to coeliac nodes.
What does the pudendal artery and nerve pass through to ext the ol pelv? what other thing goes through there?
The lesser sciatic foramen, also the tendon of internal obturator
Describe illiopsoas at the level of the symphysis:
Lateral and most bulky part is illiacus.
Where do these nodes drain:
Apical axillary
Sacral/pre sacral
Apical -> subclavian trunk - >thoracic duct
Pre sacral: Drain to any of 1) Common iliac 2) Lumbar trunks 3) Inferior mesenteric
How long is the male urethra?
Name the parts
18-22cm
Prostatic, membranous, bolbous, spongy, and navicular fossa, external urethral orifice.
How many segments of the liver are there? Give the 1 st 4 with land marks
There are 8.
The 1st is the caudate lobe
2 and 3 are left lobe (2 sup, 3 inf)
4 is high and runs the right side of falciform, laterally bounded by Cantillie’s line.
The rest circle clock wise from inferior so that 5 is superior to 8 and 6 (inferior) and 7(superior) form the borders.
Hepatic lobule components
6 portal triads (portal venue, arteriole, bile duct) at the points of a hexagram surrounding a central vein (to hepatic vein) connected by sinusoids and surrounded by hepatocytes.
Contents of middle mediastinum:
pericardium heart great vessels joining the heart ascending aorta pulmonary trunk right pulmonary artery left pulmonary artery the lower half of the superior vena cava tracheal bifurcation and both main bronchi phrenic nerves cardiac plexus tracheobronchial lymph nodes
sub sites of the oropharynx:
1) base of tongue,
2) tonsil and pillars, and
3) uvula, soft palate, and (4 is often included in 3)
4) posterior pharyngeal wall.
Lymphatic drainage of the subsides of oropharynx:
Tonsils:
Channels drain unilaterally (WELL LATERALISED TONSILS) through the reteropharynx/peripharyngeal space to jugulodiagstric/deep cervical nodes.
BOT:
Midline drains bilaterally to jugulodigastrics. and more laterally, drains unilaterally to those.
Soft palate, uvula (sometimes posterior wall included):
(1) medially to the middle third of the jugular chain,
(2) laterally to the retropharyngeal (RP) lymphatics, and
(3) anteriorly to the hard palate and subsequently into the submental and submandibular nodal group
Posterior pharyngeal wall (the epiglottis, the borders of the tonsillar complexes, and the lateral aspects of the piriform sinuses inferiorly): Drains bilaterally Predominately to IIA, also to middle deep Cx nodes (occasionally to posterior triangle).
things in the nasopharynx:
Torus Tubaris Tubal tonsils Opening of eustachian tubes Salpingopharygeal recess Pharyngeal recess
Drainage of the nasopharynx
Laterally (predominant pathway) through superior constrictors to drain into uppermost deep cervical drains (can also drain to level Va).
Posterior (roof and posterior wall): drain to upper retropharygeal nodes.
Formula for BED:
BED = n x d (1 + d/α/β)
where n = number of fractions, d=dose/#
Formula for EQD2:
EQD= D((d+α/β)/(2+α/β))
Describe the sublingual gland
Paired almond shaped and sized salivary gland (the smallest of the 3 paired man salivary glands) in the anterior floor of mouth. Lobes either side of midline/frenulum of tongue. Covered superiorly by floor of mouth mucosa.
Produces mucinous saliva.
Excreted though 5-8 lateral ducts (of Rivinus) and large/main anterior duct (Bartholen’s) which empties via the caruncles on each side of the frenulum.
Describe the submandibular gland
1 of three paired salivary glands
Ovoid in shape and roughly thumb sized.
Produces a mix of serous and mucous saliva.
Lies along the body of the mandible, both partly deep and partly superficial to the mylohyoid
muscle.
Describe the parotid
Paired/bilateral structure. Largest of the 3 paired salivary glands. The superficial surface is approximately triangular, 5cm high, 4cm deep, 3cm wide.
Lobulated irregular shaped, it can be divided into deep and superficial lobes, separated by the facial nerve.
Along with the masseter lies within a depression known as the parotid region (this region has SCM as posterior border, zygomatic arch superior, masseter anteriorly, inferior border of mandible inferiorly)
Produces serous saliva.
The hypogastric nerve arises from
And supplies?
Injury results in?
The hypogastric nerve arises from the ventral nerve roots of T12 to L3 and supplies sympathetic nerve innervation. The hypogastric nerve may be associated with the visceral fascia of the mesorectum.
Injury to the hypogastric plexus results in increased bladder tone, impaired ejaculation, and dyspareunia.
What do you always forget to draw when drawing the stomach?
Angular incisure, also point out the cardia
Which adductor muscle makes up the posterior wall of the adductor canal?
What forms the roof and lateral?
Contents?
Adductor longus
Sartorial forms roof
Initially rectus femurs forms wall, then more inferiorly it rectus medius.
femoral artery and vein, branches of femoral nerve, sub sartorial nerve.
An effective dose of 1 Sv has a risk of?
An effective dose of 1 Sv has a risk of 5.5% chance of developing malignancy.
For I-131:
Type radiation
Half life
Form
90% Beta, 10% gamma
8 days
Liquid
Half life of samarium-153?
What is good about that
2 days, effective half-life is only 2 hours
Good if the person wants to be cremated.
Label diagram of linac head
Thoraeus filter
Sn->Cu->Al
Used for orthovoltage beams to harden beam without reducing the intensity of the beam to unacceptably low levels.
- Not required for MV range photon beams because the beam is sufficiently filtered/hardened by inherent filtration and flattening filter.
Microscopic structure of skin
- Epidermis: Stratum corner, stratum lucidum, stratum granulosum, stratum spinous, stratum basale
- Basal lamina
- Dermis containing small vessels, nerve endings, sweat glands, sebaceous glands, connective tissue, hair follicle
- Hypodermis/subcutaneous fat
Lymphatic drainage of lungs
Define: Coherent scatter
- Photon interacts with orbital electron, small scatter angle, no kinetic energy loss
- probability proportional to Z^2/E
Define Photoelectric effect
- Photon interacts with tightly-bound inner electron
- All energy absorbed (photon disappears)
- Electron is ejected from atom (Ek = Ephoton – binding energy)
- Outer electron fills inner shell vacancy and emits characteristic x-ray
- ## Occurs in range <1MVThe probability of photoelectric interaction is:
◆ Directly proportional to the atomic number cubed (Z^3),
◆ Inversely proportional to the energy of the photon cubed (E^−3).
Compton (incoherent) scattering
- Photon interacts with loosely bound (outer shell) electron
- Electron is ejected and photon is scattered at angles
- Characteristic x-ray as per photoelectric
Increasing the photon energy results in more electrons and photons being scattered in the forward direction
The probability of Compton interaction:
◆ Decreases with increasing photon energy in the MV range
◆ Is independent of the atomic number of the material in which the photon is
interacting.
Pair Production
- Photon interacts with coulomb field of nucleus and is completely absorbed
- Produces electron-positron pair, threshold energy is 1.022MV
- Positron annihilated, producing 2 x-rays (oppositely directed)
- Probability proportional to E and Z, incidence increases >10MV range
Graph of photon interactions with matter
Brachial Plexus
Roots - C5,C6,C7,C8,T1
Trunks - Superior, Middle, Inferior
Divisions -
Cords - Lateral, midial, posterior
Branches/nerves: Musculocutaneous, Axillary, Median, Ulnar, Radial (MAMUR)
5 axillary lymph node groups and their location
- Anterior (pectoral) group
- Located on medial wall of axilla - Posterior group (Subscapular)
- Along posterior axillary fold and sub scapular vessels - Lateral group (Humeral)
- Along lateral wall of axilla - Central group
- Situated deep to pec minor (i.e. level II axilla) - Apical group
- Situated at apex of axilla, medial to axillary vein (i.e. level III axilla)
Recurrent laryngeal nerve anatomy
Course of thoracic duct
Superior Mediastinum borders
The superior mediastinum is bordered by the following thoracic structures:
Superior – Thoracic inlet.
Inferior – Continuous with the inferior mediastinum at the level of the sternal angle.
Anterior – Manubrium of the sternum.
Posterior – Vertebral bodies of T1-4.
Lateral – Pleurae of the lungs.
o Describe the course and relations of the right ureter in the abdomen
- Begins at the right renal pelvis/hilum at level of L2 vertebra. Approx 25cm long
- Abdominal part: Descends vertically in retroperitoneum along the medial edge of psoas, then enters the pelvis in front of SI joint (crossing anteriorly over bifurcation of common iliac artery)
- Pelvic Part: travels down lateral pelvic wall. At the level of the ischial spines, they turn anteromedially moving in a transvers plane towards the bladder. Pierces the bladder at its lateral aspect in an oblique manner. This creates a one way valve.
- Runs under the uterine artery (vas deferens in Men)“water under the bridge”
- Relations:
* Anteriorly – parietal peritoneum, duodenum, teminal ileum, R gonadal artery, vas deferens
* Posteriorly: Right Psoas, TVPs of L2-L5, bifurication of R common iliac artery.
Dermatomes and Myotomes
Course of thoracic duct
Nerves exiting via Jugular Foramen
Contents of superior orbital fissure
Trigeminal nerve
Pancreas - parts
Cartilages of the larynx
9 total, 3 unpaired and 6 paired.
Unpaired: Thyroid cartilage, cricoid cartilage, epiglottis
Paired: Arytenoid cartilages, Corniculate cartilages, Cuneiform cartilages,
H+N nodes and possible sites of malignancy
Manchester v Paris system brachytherapy table
Define Point A and point B in Manchester intracavitary system
Describe the design and operation of a remote afterloading HDR brachytherapy unit.
A remote afterloading HDR unit contains a tungsten alloy safe to store the source, a source welded to a steel cable, a dummy source, an indexer to place the transfer tubes in, an indexer locking ring which locks the transfer tubes in place, an emergency stop button and interlock system, an internal radiation monitor and safety and treatment indicator lights. A schematic of a remote afterloading HDR unit is detailed below.
When the system is not in use the Ir-192 source, welded to a stainless steel cable, resides in a tungsten safe in the afterloader.
Before treatment, a dummy source (slightly larger) on a separate steel cable will drive out to the applicator first, to ensure the pathway is clear.
A motorised stepping motor drives the source from the afterloader to the applicator in the patient.
Once treatment is complete the source is retracted to the afterloader.
Information about the source position from each motor is fed back to the TCS so that the user knows which dwell position is being treated.
