ARRT Radiation Therapy flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Alopecia onset after radiation

Scalp hair loss typically begins 2 to 3 weeks after the first conventionally fractionated treatment; regrowth usually occurs 2 to 3 months after therapy ends unless scalp dose exceeds tolerance.

Mucositis peak timing

Oral mucositis usually appears 10 to 14 days after starting radiation, peaks at 2 to 3 weeks, and heals 2 to 4 weeks after completion if dose stays within mucosal tolerance.

Radiation dermatitis progression

Erythema appears at roughly 10 to 15 fractions, dry desquamation near 30 to 40 Gy, and moist desquamation above 40 Gy when basal layer cells are depleted faster than they regenerate.

Informed consent elements

Valid consent documents diagnosis, treatment intent and technique, expected benefits, material risks, alternatives including no treatment, and confirmation the patient may withdraw at any time.

Nutrition referral threshold

Weight loss exceeding 5% of pre-treatment body weight during a radiation course warrants dietitian referral and consideration of oral supplements or enteral feeding.

Irradiated skin care rule

Wash treated skin with lukewarm water and mild soap, pat dry, and avoid sun, heat, friction, and adhesive tape; protect skin markings from being washed off.

Occupational annual dose limits

NCRP 116 limits for radiation workers are 50 mSv total effective dose per year, 150 mSv to the lens of the eye, and 500 mSv to skin and extremities.

Public dose limit

Members of the public may receive no more than 1 mSv (100 mrem) per year from a licensed facility and no more than 0.02 mSv (2 mrem) in any one hour.

Inverse square law

Exposure rate from a point source varies inversely with the square of distance: I1/I2 = (d2/d1)², so doubling distance reduces exposure to one quarter.

Half-value layer formula

Half-value layer equals 0.693 divided by the linear attenuation coefficient, and transmitted intensity follows I = I0e^(−μx) through thickness x.

Radiation area posting thresholds

Areas exceeding 0.05 mSv/h (5 mrem/h) at 30 cm are posted 'Caution: Radiation Area'; areas above 1 mSv/h (100 mrem/h) are posted 'High Radiation Area'.

Permanent implant release criteria

A patient with a permanent brachytherapy implant may be released if the estimated dose to another person is unlikely to exceed 5 mSv (500 mrem) and written instructions are given.

Gross tumor volume definition

Gross tumor volume is the visible or palpable extent of tumor shown by imaging or clinical examination; it excludes microscopic spread and subclinical disease.

Van Herk margin formula

PTV margin equals 2.5 times the systematic error standard deviation plus 0.7 times the random error standard deviation, giving 95% CTV coverage in 90% of patients.

Spinal cord dose tolerance

With conventional fractionation the spinal cord maximum point dose should stay at or below 50 Gy, or 45 Gy to the full cord cross-section, to limit myelopathy risk.

Parotid gland constraint

Keeping mean parotid dose below 26 Gy, or at least one gland below 20 Gy, reduces the risk of grade 2 or worse xerostomia after head and neck irradiation.

Electron practical range rule

In water, practical range in centimeters is roughly the electron energy in MeV divided by 2, and the 90% depth dose falls near E/3 to E/4 centimeters.

Equivalent square field size

The equivalent square side S equals 2ab/(a+b), where a and b are the rectangular field dimensions; it is used for percent depth dose and scatter factor lookups.

Purpose of bolus

Bolus on the skin builds up dose in the buildup region so superficial lesions receive full prescription dose, and it can compensate for irregular surface contour.

Daily output constancy tolerance

TG-142 sets daily photon output constancy at plus or minus 3% of baseline, monthly output at plus or minus 2%, and annual calibration at plus or minus 1%.

Winston-Lutz test

An SRS and SBRT quality assurance test confirming the radiation field center matches mechanical isocenter within 1 mm across multiple gantry, collimator, and couch angles.

Total body irradiation dose rate

Total body irradiation is commonly delivered at 5 to 10 cGy per minute to reduce pulmonary toxicity; 12 Gy in 6 fractions over 3 days is a frequent pre-transplant regimen.

Deep inspiration breath hold

Breath hold at deep inspiration increases the distance between heart and chest wall, lowering mean cardiac dose during left breast irradiation and reducing late cardiac risk.

SBRT localization requirement

SBRT demands isocentric target localization within 1 mm, usually achieved with cone-beam CT or orthogonal imaging plus 6D couch correction before every fraction.

VMAT delivery concept

Volumetric modulated arc therapy rotates the gantry while continuously varying dose rate, gantry speed, and multileaf collimator positions to produce a conformal dose distribution.

Half-beam block purpose

A half-beam block places the collimated field edge at midline so adjacent fields, such as cranial and spinal fields, match without divergent overlap in the junction region.

TG-51 reference calibration

Photon calibration uses 10 cm depth in water, 100 cm SSD, a 10 × 10 cm field, and Dw = M·N_Dw·P_ion·P_tp·P_elec·P_pol with a 0.6 cc ion chamber.

Monitor unit calculation

MU equals prescribed dose divided by the product of calibrated output, TMR at depth, collimator and phantom scatter factors, wedge factor, and inverse-square correction.

TMR from percent depth dose

TMR(d,r) = (%DD/100) × ((SSD+d)/(SSD+dmax))² × (Sp(dmax)/Sp(d)), converting depth dose measured at fixed SSD into tissue-maximum ratio.

Gamma index criterion

The gamma index combines dose difference and distance-to-agreement; 3%/3 mm with at least 95% of points passing is standard IMRT QA acceptance, while SBRT often uses 2%/2 mm.

Iodine-125 characteristics

I-125 decays by electron capture with a 59.4-day half-life and emits photons averaging about 28 keV, giving low penetration suitable for permanent prostate implants.

TG-43 dose formalism

Brachytherapy dose is D(r,θ) = Sk·Λ·[G(r,θ)/G(r0,θ0)]·g(r)·F(r,θ), where Λ is the dose-rate constant, g the radial function, and F the anisotropy function.