Patient Interactions and Management
15%of exam
Patient and Medical Record Management
8%of exam
Radiation Physics and Radiobiology
10%of exam
Radiation Protection and QA
15%of exam
Treatment Sites and Tumors
13%of exam
Treatment Volume Localization
9%of exam
Prescription and Dose Calculation
12%of exam
Treatments
18%of exam
Quick Facts
- Credential
- R.T.(T)
- Pathway
- Primary eligibility
- Items
- 230 total, 200 scored
- Pilot
- 30 unscored
- Test time
- 230 minutes
- Appointment
- 250 minutes (4h 10m)
- Pass
- Scaled 75 on 1-99
- Raw needed
- About 68% correct
- Pass rate
- 77% first attempt, 2025
- Mean score
- 79.8 scaled, 2025
- Fee
- $225
- Attempts
- 3 within 3 years
- Vendor
- Pearson VUE
- Weakest section
- Dose calculation, 7.4 mean
Acute vs Late Effects
Acute
- Rapidly dividing tissue
- During or weeks after
- Mucositis, desquamation
Late
- Slowly dividing tissue
- Months to years after
- Fibrosis, necrosis
Fast tissue vs slow tissue
Urgent Situation Picker
- Unresponsive, no pulse→Call code, begin CPR
- Beam will not terminate→Press emergency off
- New back pain, leg weakness→Notify physician immediately(Cord compression)
- Contrast leaking at site→Stop injection, elevate limb
- Seizure during setup→Protect head, do not restrain
- Patient falls in vault→Stop beam, assess first
- Fever with low counts→Report before treating(Neutropenic sepsis)
Ethics and Legal
- Informed consent
- Explained, voluntary, documented
- Implied consent
- Emergency, unresponsive patient
- HIPAA
- Protects health information
- Assault
- Threat of harm
- Battery
- Unlawful touching
- Negligence
- Failure of reasonable care
- Respondeat superior
- Employer answers for employee
- Res ipsa loquitur
- Thing speaks for itself
- Immobilizer
- Positioning aid, patient consents
- Restraint
- Needs order and documentation
- Advance directive
- Patient wishes if incapacitated
Infection Control
- Chain of infection
- Pathogen to susceptible host
- Portal of exit
- Leaves the reservoir
- Portal of entry
- Enters the new host
- Fomite
- Contaminated inanimate object
- Vector borne
- Carried by living organism
- Standard Precautions
- All patients, all fluids
- Contact precautions
- Gown and gloves
- Droplet precautions
- Surgical mask, close range
- Airborne precautions
- N95, negative pressure room
- Neutropenic precautions
- Protects the patient instead
Side Effects by Dose
- Erythema
- Around 20-25 Gy
- Dry desquamation
- Around 30-40 Gy
- Moist desquamation
- Around 45-50 Gy
- Mucositis
- Head and neck, week 2
- Xerostomia
- Parotid mean above 26 Gy
- Esophagitis
- Thoracic fields, mid course
- Diarrhea
- Pelvic and abdominal fields
- Myelosuppression
- Large marrow volumes irradiated
- Acute effects
- Rapidly dividing tissues
- Late effects
- Fibrosis, telangiectasia, necrosis
Labs and Tumor Markers
- WBC normal
- 4,500-11,000 per mm3
- Platelets normal
- 150,000-400,000 per mm3
- Hemoglobin normal
- About 12-17 g/dL
- ANC below 500
- Severe neutropenia
- PSA
- ProstateMarker
- CEA
- ColorectalMarker
- CA-125
- OvarianMarker
- CA 19-9
- PancreaticMarker
- AFP
- Liver and testicularMarker
- hCG
- Testicular and gestationalMarker
Chart and Documentation
- Prescription
- Site, dose, fractions, energy
- Monitor units
- Machine output delivered
- Cumulative dose
- Running total to date
- Fraction number
- Treatments already delivered
- Elapsed days
- Calendar days since start
- b.i.d. timing
- Minimum 6 hours apart
- Variance
- Documented prescription change
- Medical event
- 20% total dose deviation
- Wrong site or patient
- Reportable medical event
- Charge capture
- Professional plus technical components
Four R's of Radiobiology
Repair, Redistribution, Repopulation, Reoxygenation
Repair: sublethal damageRedistribution: into sensitive phaseRepopulation: tumor regrowsReoxygenation: hypoxic cells oxygenate
Gray vs Sievert
Gray
- Absorbed dose
- Energy per mass
- 1 Gy equals 100 rad
Sievert
- Dose equivalent
- Weighted for damage
- 1 Sv equals 100 rem
Energy deposited vs biological risk
Units and Conversions
- Absorbed dose
- Gray, joule per kilogramSI
- 1 Gy
- 100 rad
- 1 cGy
- 1 rad
- Dose equivalent
- SievertSI
- 1 Sv
- 100 rem
- Exposure
- Coulomb per kilogram
- Air kerma
- Gray, energy released
- Activity
- Becquerel, one decay/secondSI
- 1 curie
- 3.7 x 10^10 becquerel
- Effective dose
- Sievert, weighted whole body
Cell Cycle Sensitivity
M and G2 sensitive, late S resistant
M: mitosis, most sensitiveG2: sensitiveLate S: most resistant
Deterministic vs Stochastic
Deterministic
- Has a threshold
- Severity rises with dose
- Cataract, erythema
Stochastic
- No threshold assumed
- Probability rises with dose
- Cancer, genetic effects
How bad vs how likely
Photon Interactions
- Compton
- Dominant at therapy energies
- Compton depends on
- Electron density, not Z
- Photoelectric
- Rises with Z cubed
- Pair production
- Threshold 1.02 MeV
- Photodisintegration
- Above about 10 MeV
- Coherent scatter
- Low energy, no ionization
- Bremsstrahlung
- Electron braked near nucleus
- Characteristic
- Inner shell vacancy filled
- Cobalt-60 average
- 1.25 MeV photons
- Cobalt-60 half-life
- 5.27 years
- Half-value layer
- Cuts intensity to half
- Tenth-value layer
- 3.32 half-value layers
Bergonie and Tribondeau
Immature, dividing, long mitotic future die first
Undifferentiated: sensitiveHigh mitotic rate: sensitiveNerve and muscle: resistant
Radiobiology Numbers
- Four R's
- Repair, redistribution, repopulation, reoxygenation
- Most sensitive phase
- M and late G2
- Most resistant phase
- Late S
- Bergonie and Tribondeau
- Immature, dividing cells sensitive
- Oxygen effect
- OER about 2.5-3
- High LET
- OER near 1
- RBE peak
- Near 100 keV per micron
- Alpha/beta tumors
- About 10 Gy
- Alpha/beta late tissue
- About 3 Gy
- Deterministic
- Threshold, severity rises
- Stochastic
- No threshold, probability rises
- Radiosensitizer
- Oxygen, cisplatin, 5-FU
- Radioprotector
- Amifostine
TD 5/5 Whole Organ
- Lens
- 10 Gy, cataract
- Kidney, both
- 23 Gy
- Lung, whole
- 17.5 Gy
- Liver, whole
- 30 Gy
- Heart
- 40 Gy, pericarditis
- Spinal cord
- About 45-50 Gy
- Optic chiasm
- 50 Gy
- Small bowel
- 40 Gy
- Rectum
- 60 Gy
- Bladder
- 65 Gy
- Brain
- About 45-60 Gy
- TD 5/5 means
- 5% complications, 5 years
ALARA Trio
Time down, Distance up, Shielding on
Time: shorten exposureDistance: inverse squareShielding: concrete and lead
Primary vs Secondary Barrier
Primary
- Faces the useful beam
- Thickest concrete
- Sized by workload
Secondary
- Leakage and scatter only
- Thinner barrier
- Includes maze walls
Useful beam vs stray radiation
Dose Limits (NCRP 116)
- Occupational, annual
- 50 mSv, 5 rem
- Occupational, cumulative
- 10 mSv times age
- Lens of eye
- 150 mSv per year
- Skin, hands, feet
- 500 mSv per year
- Embryo, whole gestation
- 5 mSv after declaration
- Embryo, monthly
- 0.5 mSv
- Public, continuous
- 1 mSv per year
- Public, infrequent
- 5 mSv per year
- Trainee under 18
- 1 mSv per year
- Negligible individual dose
- 0.01 mSv per year
Klystron vs Magnetron
Klystron
- Amplifies microwaves
- Needs an RF driver
- High energy linacs
Magnetron
- Generates microwaves
- Self contained oscillator
- Lower energy linacs
Amplifier vs generator
Area Postings (10 CFR 20)
- Restricted area
- Access controlled for protection
- Unrestricted area
- Public limits apply
- Radiation area
- 0.05 mSv/hr at 30 cm
- High radiation area
- 1 mSv/hr at 30 cm
- Very high radiation area
- 5 Gy/hr at 1 m
- ALARA
- Time, distance, shielding
- Primary barrier
- Intercepts the useful beam
- Secondary barrier
- Stops leakage and scatter
- Neutron door
- Needed above 10 MV
- Workload, use, occupancy
- Drive barrier thickness
Linac QA Tolerances (TG-142)
- Daily output
- Within 3%
- Daily lasers
- Within 2 mm
- Daily distance indicator
- Within 2 mm
- Monthly output
- Within 2%
- Light and radiation field
- Within 2 mm
- Gantry, collimator angle
- Within 1 degree
- Annual output calibration
- Within 1%
- MLC leaf position
- Within 1 mm
- Winston-Lutz isocenter
- Within 1 mm
- IMRT gamma criteria
- 3% and 3 mm
- Reference calibration
- 1 cGy per monitor unit
Linac and Detectors
- Magnetron
- Generates microwaves
- Klystron
- Amplifies microwaves
- Waveguide
- Accelerates the electrons
- Bending magnet
- Usually 270 degrees
- Target
- Tungsten, makes bremsstrahlung
- Flattening filter
- Evens the photon profile
- Scattering foil
- Spreads the electron beam
- Monitor chambers
- Count and terminate MU
- Ionization chamber
- Output calibration
- Geiger-Muller
- Contamination and leak survey
- TLD and OSL
- Personnel dosimeter badges
- Diode
- In vivo entrance dose
- Neutron detector
- High energy vaults
Grade vs Stage
Grade
- Cell differentiation
- Microscopic appearance
- G1 through G4
Stage
- Anatomic extent
- Size, nodes, spread
- TNM groupings
How ugly vs how far
Staging and Classification
- TNM
- Tumor, nodes, metastasis
- Tis
- Carcinoma in situ
- NX
- Nodes cannot be assessed
- M1
- Distant metastasis present
- Grade G1-G4
- Differentiation and growth rate
- Ann Arbor
- Lymphoma staging
- B symptoms
- Fever, sweats, weight loss
- FIGO
- Gynecologic staging
- Carcinoma
- Epithelial, spreads lymphatically
- Sarcoma
- Connective tissue, spreads hematogenously
- Seminoma
- Highly radiosensitive
- Melanoma
- Relatively radioresistant
Spread and Emergencies
- Prostate metastasis
- Osteoblastic bone lesions
- Breast nodes
- Axillary levels I-III
- Small cell lung
- Early widespread metastasis
- Lung metastasis targets
- Brain, bone, liver, adrenal
- Cord compression
- Steroids, then urgent radiation
- SVC syndrome
- Facial swelling and dyspnea
- Hypercalcemia
- Confusion, thirst, arrhythmia
- Febrile neutropenia
- Fever with low ANC
- Raised intracranial pressure
- Headache, vomiting, papilledema
- Whole brain palliation
- Opposed lateral fields
Volume Growth Order
GTV inside CTV inside ITV inside PTV
GTV: seen diseaseCTV: suspected spreadITV: motion addedPTV: setup error added
CTV vs PTV
CTV
- Biological volume
- Microscopic disease
- Physician drawn
PTV
- Geometric volume
- Motion and setup error
- Never treated alone
Disease extent vs geometric uncertainty
Immobilization Picker
- Brain or head/neck→Thermoplastic mask(3 or 5 point)
- Cranial stereotactic→Frame or rigid mask(Plus daily imaging)
- Breast tangents→Breast board(Arms above head)
- Rectum or anus→Prone belly board(Displaces small bowel)
- Prostate supine→Vac-Lok, leg supports(Reproducible pelvis)
- Moving lung target→4DCT, abdominal compression(Limits excursion)
- Extremity sarcoma→Custom cradle mold(Spares strip)
ICRU Volumes
- GTV
- Visible gross tumor
- CTV
- GTV plus microscopic spread
- ITV
- CTV plus motion margin
- PTV
- Adds setup uncertainty
- OAR
- Organ at risk
- PRV
- OAR plus its margin
- Treated volume
- Inside prescription isodose
- Isocenter
- Gantry rotation center point
- DVH
- Dose against volume plot
- Hot spot
- Highest dose region
CT Simulation Setup
- Flat couch top
- Matches treatment machine
- Lasers
- External alignment reference
- Tattoos
- Permanent reference marks
- Thermoplastic mask
- Head and neck immobilization
- Alpha cradle, Vac-Lok
- Body and limb molds
- Belly board
- Prone rectum, spares bowel
- Breast board
- Arms up, chest angled
- Wing board
- Arms up for thorax
- 4DCT
- Captures respiratory motion
- Thin slices
- Sharper DRR reconstruction
- CT number
- Converted to electron density
- DRR
- Reference image for verification
Electron Range Rules
R90 = E/4, R80 = E/3, Rp = E/2
Energy in MeVRange in centimetersRp: practical range
PDD vs TMR
PDD
- SSD technique
- Referenced to dmax
- Depends on SSD
TMR
- SAD technique
- Referenced to dmax
- Independent of SSD
Surface setup vs isocentric
Beam and Energy Picker
- Target within 5 cm→Electrons(Rapid dose falloff)
- Deep pelvic target→15-18 MV photons(Better depth dose)
- Head and neck target→6 MV photons(Less lateral scatter)
- Chest wall after mastectomy→Electrons or tangents(Spares lung)
- Skin sparing not wanted→Add bolus(Brings dmax up)
- Whole skin surface→Total skin electrons(Extended distance)
- Concave target near cord→IMRT or VMAT(Steep gradient)
Dose Formulas
- Inverse square law
- Intensity falls with distance squared
- PDD
- Depth dose over dmax
- TAR
- Tissue dose over free space
- TMR
- Depth dose over dmax, SAD
- Backscatter factor
- TAR at dmax
- Equivalent square
- 4 times area over perimeter
- Mayneord F factor
- Corrects PDD for SSD
- Wedge angle
- 90 minus half hinge angle
- Gap calculation
- Half length times depth/SSD
- PDD rises with
- Energy, field size, SSD
- Wedge factor
- Raises monitor units needed
- Tray factor
- Raises monitor units needed
Dmax Ladder
Cobalt 0.5, 6 MV 1.5, 18 MV 3.3
Depths in centimetersHigher energy, deeper dmaxBolus pulls dmax up
Hyper vs Hypofractionation
Hyperfractionation
- Smaller dose per fraction
- More fractions total
- Spares late tissue
Hypofractionation
- Larger dose per fraction
- Fewer fractions total
- Shorter course
Smaller more vs larger fewer
Which Dose Quantity
- SSD setup, fixed surface→PDD
- SAD isocentric setup→TMR
- Rotational or arc therapy→TAR or TMR
- Rectangular field given→Equivalent square
- Treating at nonstandard SSD→Mayneord F factor
- Wedge in the beam→Apply wedge factor
Fractionation Schemes
- Conventional
- 1.8-2 Gy once daily
- Hyperfractionation
- Smaller doses, more fractions
- Accelerated
- Same dose, shorter time
- Hypofractionation
- Larger doses, fewer fractions
- SBRT
- Very few ablative fractions
- Split course
- Planned mid-treatment break
- Dmax, cobalt-60
- About 0.5 cm
- Dmax, 6 MV
- About 1.5 cm
- Dmax, 18 MV
- About 3.3 cm
- Electron R90
- Energy divided by 4
- Electron R80
- Energy divided by 3
- Electron practical range
- Energy divided by 2
Bolus vs Compensator
Bolus
- Sits on the skin
- Removes skin sparing
- Tissue equivalent
Compensator
- Mounted in the beam
- Corrects contour deficit
- Keeps skin sparing
On skin vs in beam
Image Guidance Picker
- Bony alignment enough→kV planar pair
- Soft tissue target→CBCT(Volumetric match)
- Prostate, daily shifts→Fiducials or CBCT
- Breast breath hold→Surface guidance(Adds no dose)
- Confirm field shape→MV portal image
- Tumor moves with breathing→Gating or tracking
Typical Site Prescriptions
- Breast, conventional
- 50 Gy in 25
- Breast, hypofractionated
- 40.05 Gy in 15
- Prostate, conventional
- 78-80 Gy in 39-40
- Prostate, SBRT
- 36.25 Gy in 5
- Head and neck, definitive
- 70 Gy in 35
- Lung, definitive
- 60-66 Gy in 30-33
- Lung, SBRT
- 54 Gy in 3
- Glioblastoma
- 60 Gy in 30
- Rectum, preoperative
- 50.4 Gy in 28
- Cervix, external beam
- 45 Gy in 25
- Whole brain
- 30 Gy in 10
- Palliative bone
- 8 Gy in 1
kV vs MV Imaging
kV
- Photoelectric contrast
- Sharp bone detail
- Lower imaging dose
MV
- Compton dominates
- Poor soft tissue contrast
- Uses treatment beam
Diagnostic contrast vs beam's-eye truth
Image Guidance
- MV portal image
- Confirms field on machine
- kV planar image
- Sharper bony detail
- CBCT
- Volumetric soft tissue match
- Fiducial markers
- Prostate daily matching
- Surface guidance
- Optical tracking, no dose
- Ultrasound localization
- Soft tissue, no dose
- Respiratory gating
- Beam on during phase
- Breath hold
- Spares heart in breast
- Abdominal compression
- Limits diaphragm excursion
- Couch shift
- Moves marks to isocenter
LDR vs HDR Brachytherapy
LDR
- 0.4-2 Gy per hour
- Longer inpatient stay
- Cesium-137, iodine-125
HDR
- Above 12 Gy per hour
- Minutes, outpatient
- Iridium-192 afterloader
Slow inpatient vs fast outpatient
Beam Modifiers
- Bolus
- Raises surface dose
- Compensator
- Corrects missing tissue
- Physical wedge
- Absorber tilts isodose curves
- Dynamic wedge
- Moving jaw makes gradient
- Cerrobend block
- Low melting shielding alloy
- Block thickness
- About 5 half-value layers
- MLC
- Replaces custom shaped blocks
- Electron cone
- Collimates close to skin
- IMRT
- Modulated fixed gantry angles
- VMAT
- Modulated while gantry rotates
Brachytherapy Basics
- LDR
- 0.4-2 Gy per hour
- MDR
- 2-12 Gy per hour
- HDR
- Above 12 Gy per hour
- Iridium-192
- HDR source, 73.8 days
- Iodine-125
- Prostate seeds, 59.4 days
- Palladium-103
- Prostate seeds, 17 days
- Cesium-137
- LDR source, 30 years
- Point A
- 2 cm up, 2 lateral
- Point B
- 5 cm lateral, pelvic sidewall
- Remote afterloading
- Keeps staff out of room
- Intracavitary
- Tandem, ovoids, cylinder
- Interstitial
- Needles or catheters implanted
Common Traps
Scaled score vs percent
75 is scaled score ≠ Not 75 percent correct
Dose vs equivalent
Gray is absorbed dose ≠ Sievert is dose equivalent
PDD vs TMR
PDD pairs with SSD ≠ TMR pairs with SAD
Bolus vs compensator
Bolus raises skin dose ≠ Compensator keeps skin sparing
Grade vs stage
Grade is cell differentiation ≠ Stage is anatomic extent
Barrier types
Primary stops useful beam ≠ Secondary stops leakage, scatter
Klystron vs magnetron
Klystron amplifies microwaves ≠ Magnetron generates microwaves
Hyper vs hypofractionation
Hyper uses smaller fractions ≠ Hypo uses larger fractions
Brachytherapy points
Point A near tandem ≠ Point B at sidewall
Immobilizer vs restraint
Immobilizer is positioning aid ≠ Restraint needs physician order
Compton dependence
Compton follows electron density ≠ Photoelectric follows atomic number
Last Minute
- 1.Pass = scaled 75, not 75%
- 2.Scored 200, pilot 30, total 230
- 3.Test time 230 min, appointment 250
- 4.Gray = absorbed; Sievert = equivalent
- 5.PDD = SSD; TMR = SAD
- 6.Occupational limit 50 mSv yearly
- 7.Fetal limit 5 mSv whole gestation
- 8.Lens limit 150 mSv yearly
- 9.Bolus adds dose to skin
- 10.GTV inside CTV inside PTV
- 11.Compton dominates megavoltage therapy beams
- 12.Cord tolerance about 45-50 Gy
- 13.Daily output tolerance is 3%
- 14.Cerrobend blocks are 5 HVLs
- 15.Equivalent square = 4 area/perimeter
- 16.Prostate metastases are osteoblastic
- 17.Dose calculation scored lowest nationally
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