ABPS Radiation Oncology flashcards

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

Alpha/beta ratio

The dose at which linear and quadratic components of cell killing are equal in the linear-quadratic model; approximately 10 Gy for tumors and acute effects, 3 Gy for late effects.

Biologically effective dose

BED = nd(1 + d/(α/β)), where n is fraction number and d is dose per fraction; it compares regimens with different fractionation using a chosen α/β value.

Oxygen enhancement ratio

The ratio of dose under hypoxic versus well-oxygenated conditions producing the same effect; typically 2.5-3.0, explaining radioresistance of hypoxic tumor cells.

EQD2

Equivalent dose in 2-Gy fractions, calculated as BED divided by (1 + 2/(α/β)); used to compare fractionation schemes on a common scale.

Gray definition

The SI unit of absorbed dose; one gray equals one joule per kilogram of irradiated material.

Photoelectric effect

Photon absorption by an inner-shell electron, dominant at low energies and high atomic number; probability scales approximately with Z³/E³.

Inverse square law

Dose rate from a point source decreases with the square of distance (1/r²); used for source strength and distance calculations in planning.

TG-43 formalism

AAPM brachytherapy dosimetry model expressing dose rate via source strength, dose-rate constant, geometry factor, radial dose function, and anisotropy function.

Iodine-125 half-life

Approximately 59.4 days; used for permanent prostate implants with a monotherapy prescription dose around 145 Gy.

Tandem and ovoid applicator

Gynecologic brachytherapy applicator placing a central tandem in the uterus and ovoids in the vagina; used for cervical cancer HDR or LDR implants.

Radium-223 mechanism

Alpha-emitting calcium mimetic that targets bone metastases; used in metastatic castration-resistant prostate cancer to improve survival and reduce skeletal events.

Percent depth dose

Ratio of dose at depth to dose at a reference depth along the central axis; increases with beam energy and field size and decreases with depth.

VMAT delivery

Volumetric modulated arc therapy delivers dose during continuous gantry rotation with dynamic multileaf collimator motion, reducing monitor units and treatment time versus fixed-field IMRT.

SBRT definition

Stereotactic body radiation therapy delivers high dose per fraction in few fractions with steep dose gradients, requiring precise immobilization and image guidance.

TG-218 IMRT QA

AAPM task group report providing guidance on IMRT measurement-based and calculation-based verification, gamma analysis criteria, and action limits.

TG-142 linac QA

AAPM report specifying quality assurance tests and tolerances for linear accelerators, including daily output constancy, monthly mechanical checks, and annual calibration.

Four-dimensional CT

Imaging that incorporates respiratory phase to characterize tumor motion; used to define internal target volumes and gating windows for thoracic and abdominal RT.

Concurrent chemoradiation

Delivery of radiosensitizing chemotherapy during a course of radiotherapy; standard for locally advanced NSCLC, head and neck, and cervical cancers.

Radiation recall

Inflammatory reaction occurring in previously irradiated tissue after exposure to a triggering systemic agent such as doxorubicin or gemcitabine; managed supportively.

Radiation pneumonitis

Symptomatic lung inflammation occurring one to six months after thoracic irradiation, presenting with cough and dyspnea; corticosteroids are the main treatment.

Lhermitte syndrome

Transient electric-shock sensation radiating down the spine with neck flexion after cervical cord irradiation; usually self-limited and resolves without intervention.

Oral mucositis prevention

Consists of meticulous oral care and consideration of palifermin in selected high-risk patients; low-level laser therapy may reduce severity during head and neck RT.

Single-fraction bone RT

Eight gray in one fraction provides pain relief comparable to longer courses for bone metastases, with a higher rate of subsequent retreatment.

Spinal cord compression

Oncologic emergency requiring urgent corticosteroids and decompressive surgery or radiotherapy; RT alone is used when surgery is not feasible.

Superior vena cava syndrome

Obstruction of the SVC often from lung cancer or lymphoma; managed with urgent radiotherapy or endovascular stent placement, especially with airway compromise.

Hippocampal-sparing WBRT

Whole-brain radiotherapy technique that reduces dose to the hippocampi to limit cognitive decline, used in selected patients with brain metastases.

Hypercalcemia of malignancy

Metabolic emergency treated with intravenous fluids plus bisphosphonates or denosumab; radiotherapy is reserved for painful bone lesions.

Just culture

A safety framework that encourages reporting of errors and near-misses while distinguishing system failures from reckless behavior; supports incident learning systems.

Pretreatment time-out

A required verification step confirming patient identity, treatment site, laterality, and plan before each treatment to prevent wrong-site errors.

ALARA principle

As low as reasonably achievable; radiation safety principle minimizing exposure through time, distance, and shielding, applied to staff and patients.

Informed consent elements

Required discussion of benefits, risks, alternatives, and the right to decline, documented before initiating radiotherapy or other oncologic treatment.

Glottic cancer T1 management

Early glottic cancer is treated with single-modality transoral laser microsurgery or definitive radiotherapy; routine neck dissection is not indicated for N0 disease.