ABR TMP flashcards

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

Mayneord F factor

Ratio used to convert percent depth dose from one source-to-surface distance to another; it multiplies squared inverse-square terms evaluated at maximum depth and at the depth of interest.

Paddick conformity index

Target volume inside the prescription isodose, squared, divided by the product of total target volume and prescription isodose volume; it penalizes both undercoverage and dose spill outside the target.

Gamma index

Patient-specific QA metric combining dose difference and distance-to-agreement; a point passes if a nearby point satisfies both criteria, and typical intensity-modulated criteria are three percent dose and three millimeters distance.

Biologically effective dose

BED equals n times d times one plus d divided by the alpha-beta ratio, where n is the number of fractions and d is dose per fraction; it compares fractionation schemes for a given tissue.

Equivalent square field size

A square field with the same collimator scatter as a rectangular field, estimated as four times area divided by perimeter; it lets tabulated square-field output and depth-dose data be applied.

TERMA

Total energy released per unit mass by primary photons within a voxel; convolution-superposition algorithms deposit this energy using a dose-spread kernel to obtain absorbed dose.

Acuros XB

Deterministic linear Boltzmann transport equation solver that computes dose in heterogeneous media more accurately than pencil-beam methods, particularly for lung, bone, and small radiation fields.

Temperature-pressure correction

P_TP equals 760 divided by pressure in millimeters of mercury, multiplied by 273.15 plus temperature in Celsius divided by 295.15; it corrects ion chamber readings to reference conditions.

Two-voltage method

Determines the ion chamber recombination correction by measuring collected charge at two bias voltages, usually full and half, and solving the standard quadratic expression from their ratio.

Winston-Lutz test

Verifies coincidence of radiation and mechanical isocenters using a small collimated field and a marker at known couch positions across multiple gantry, collimator, and couch angles; tolerance is about one millimeter.

TG-142 daily output tolerance

Daily photon and electron output constancy must stay within three percent of baseline, while the monthly calibration tolerance is two percent and the annual tolerance is one percent.

Picket fence test

Imaging test in which multileaf collimator leaves form alternate closed and open strips; it detects leaf position errors, calibration drift, and abnormal interleaf leakage.

Dosimetric leaf gap

Treatment planning system parameter that compensates for rounded leaf ends and leaf transmission in a multileaf collimator model; it is tuned by comparing calculated with measured doses.

Energy constancy tolerance

Per TG-142, photon beam energy constancy must remain within two percent of baseline and electron energy within three percent, determined from a ratio of chamber readings at two depths.

Air kerma strength

Brachytherapy source strength equal to air kerma rate in free space multiplied by squared distance; one unit equals one microgray square meter per hour or one centigray square centimeter per hour.

Dose rate constant lambda

Absorbed dose rate in water at one centimeter from the source along its transverse axis, divided by air kerma strength; a typical iridium-192 value is about 1.11 centigray per hour per unit.

Iridium-192 half-life

Approximately 73.8 days, with a mean photon energy near 380 keV; it is the standard high-dose-rate brachytherapy radionuclide and a source is typically exchanged every three to four months.

Point A

Classic gynecologic brachytherapy reference point located two centimeters lateral to the intrauterine tandem and two centimeters superior to the external cervical os along the applicator.

D2cc

Minimum dose covering the most irradiated two cubic centimeters of an organ at risk; this volume-based parameter is less sensitive to individual point placement than ICRU 38 reference points.

Well chamber

Reentrant ionization chamber used to measure brachytherapy source air kerma strength; it is calibrated against a national standard and corrected for temperature, pressure, and source geometry.

Stoichiometric CT calibration

Method that converts computed tomography Hounsfield units into electron density using tissue-equivalent inserts, enabling accurate heterogeneity correction in dose calculation algorithms.

Four-dimensional CT

Respiratory-correlated computed tomography that sorts images by breathing phase or amplitude, used to define internal target volumes and motion margins for thoracic and abdominal radiotherapy.

Cone-beam CT limitations

Scatter and truncation degrade Hounsfield unit accuracy, so cone-beam computed tomography is used for setup verification rather than primary dose calculation; imaging dose is typically a few milligray per scan.

RTSTRUCT object

DICOM radiotherapy object that stores structure contours, names, and references to the planning image series; it transfers target and organ delineations between contouring and planning systems.

MRI geometric distortion

Spatial inaccuracy in magnetic resonance images arising from gradient nonlinearity and field inhomogeneity; AAPM Task Group 284 addresses acceptance testing, quality assurance, and distortion correction for simulation.

Surface-guided radiation therapy

Uses stereoscopic cameras or structured light to track the patient skin surface in three dimensions for setup and intrafraction motion monitoring, adding no ionizing radiation dose.

NCRP Report 151

Provides structural shielding design methods for megavoltage photon and electron radiotherapy facilities, covering workload, use factor, occupancy factor, distance, and tenth-value-layer thickness calculations.

Use factor

Fraction of the workload during which the primary beam is directed at a particular barrier; it is one for the floor and commonly one quarter for walls in a four-field arrangement.

Occupancy factor

Fraction of time an area beyond a barrier is occupied by the same individual; it is one for offices and work areas and lower for corridors, restrooms, and infrequently used spaces.

Linac leakage limit

Leakage radiation from a medical linear accelerator must not exceed 0.2 percent of the useful beam dose rate at any point, with an average no greater than 0.1 percent.

TG-100 FMEA

Failure mode and effects analysis scores each process step for severity, occurrence, and detectability; the risk priority number is the product of the three scores and ranks hazards for mitigation.

TG-263 nomenclature

AAPM report establishing standardized names for targets, organs at risk, and plan structures so that radiotherapy data can be exchanged, pooled, and analyzed consistently across institutions.