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ARRT Radiation Therapy Cheat Sheet

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Patient Interactions and Management

  • 15% of exam
  • 29 scored items Ethics and Legal Infection Control Side Effects by Dose Urgent Situation Picker

Patient and Medical Record Management

  • 8% of exam
  • 17 scored items Labs and Tumor Markers Chart and Documentation Medical event rule

Radiation Physics and Radiobiology

  • 10% of exam
  • 21 scored items Units and Conversions Photon Interactions Radiobiology Numbers TD 5/5 Whole Organ

Radiation Protection and QA

  • 15% of exam
  • 30 scored items Dose Limits Area Postings Linac QA Tolerances Linac and Detectors

Treatment Sites and Tumors

  • 13% of exam
  • 26 scored items Staging and Classification Spread and Emergencies Grade vs Stage

Treatment Volume Localization

  • 9% of exam
  • 18 scored items ICRU Volumes CT Simulation Setup Immobilization Picker

Prescription and Dose Calculation

  • 12% of exam
  • 24 scored items Dose Formulas Fractionation Schemes Which Dose Quantity Lowest 2025 section score

Treatments

  • 18% of exam
  • 35 scored items Typical Site Prescriptions Image Guidance Beam Modifiers Brachytherapy Basics

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 IN

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 IN

  • 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 IN

  • 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 IN

  • 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 IN

  • 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 RE

  • 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 Prostate Marker
  • CEA Colorectal Marker
  • CA-125 Ovarian Marker
  • CA 19-9 Pancreatic Marker
  • AFP Liver and testicular Marker
  • hCG Testicular and gestational Marker

Chart and Documentation RE

  • 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 PH

  • Repair, Redistribution, Repopulation, Reoxygenation
  • Repair: sublethal damage Redistribution: into sensitive phase Repopulation: tumor regrows Reoxygenation: hypoxic cells oxygenate

Gray vs Sievert PH

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 PH

  • Absorbed dose Gray, joule per kilogram SI
  • 1 Gy 100 rad
  • 1 cGy 1 rad
  • Dose equivalent Sievert SI
  • 1 Sv 100 rem
  • Exposure Coulomb per kilogram
  • Air kerma Gray, energy released
  • Activity Becquerel, one decay/second SI
  • 1 curie 3.7 x 10^10 becquerel
  • Effective dose Sievert, weighted whole body

Cell Cycle Sensitivity PH

  • M and G2 sensitive, late S resistant
  • M: mitosis, most sensitive G2: sensitive Late S: most resistant

Deterministic vs Stochastic PH

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 PH

  • 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 PH

  • Immature, dividing, long mitotic future die first
  • Undifferentiated: sensitive High mitotic rate: sensitive Nerve and muscle: resistant

Radiobiology Numbers PH

  • 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 PH

  • 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 PR

  • Time down, Distance up, Shielding on
  • Time: shorten exposure Distance: inverse square Shielding: concrete and lead

Primary vs Secondary Barrier PR

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) PR

  • 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 PR

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) PR

  • 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) PR

  • 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 PR

  • 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 SI

Grade

  • Cell differentiation
  • Microscopic appearance
  • G1 through G4

Stage

  • Anatomic extent
  • Size, nodes, spread
  • TNM groupings
  • How ugly vs how far

Staging and Classification SI

  • 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 SI

  • 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 LO

  • GTV inside CTV inside ITV inside PTV
  • GTV: seen disease CTV: suspected spread ITV: motion added PTV: setup error added

CTV vs PTV LO

CTV

  • Biological volume
  • Microscopic disease
  • Physician drawn

PTV

  • Geometric volume
  • Motion and setup error
  • Never treated alone
  • Disease extent vs geometric uncertainty

Immobilization Picker LO

  • 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 LO

  • 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 LO

  • 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 DO

  • R90 = E/4, R80 = E/3, Rp = E/2
  • Energy in MeV Range in centimeters Rp: practical range

PDD vs TMR DO

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 DO

  • 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 DO

  • 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 DO

  • Cobalt 0.5, 6 MV 1.5, 18 MV 3.3
  • Depths in centimeters Higher energy, deeper dmax Bolus pulls dmax up

Hyper vs Hypofractionation DO

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 DO

  • 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 DO

  • 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 TR

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 TR

  • 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 TR

  • 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 TR

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 TR

  • 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 TR

LDR

  • 0.4-2 Gy per hour
  • Longer inpatient stay
  • Seeds or temporary implants

HDR

  • Above 12 Gy per hour
  • Minutes, outpatient
  • Remote afterloader
  • Slow inpatient vs fast outpatient

Beam Modifiers TR

  • 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 TR

  • LDR 0.4-2 Gy per hour
  • MDR 2-12 Gy per hour
  • HDR Above 12 Gy per hour
  • ARRT scope Basic concepts of common uses
  • Not covered Specific procedures, isotope characteristics
  • Treatment option Indications, benefits, risks
  • Surrounding tissue dose Drops steeply with distance
  • Radiation protection Time, distance, shielding
  • Radioactive materials Handle and dispose per protocol
  • 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 depth

  • Basic concepts and protection only ≠ Isotope characteristics not covered

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

ARRT Radiation Therapy

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