Free ARRT Radiation Therapy Exam Flashcards

Definitive intent aims to eradicate the tumor and uses a high total dose delivered in many small fractions (conventionally 1.8-2 Gy each) to protect normal tissue. Palliative intent aims to relieve symptoms such as pain, bleeding, or obstruction, so it uses a lower total dose in fewer, larger fractions to finish quickly. Knowing the stated intent tells you why a short hypofractionated course is appropriate rather than a prescription error.

Immobilization devices such as thermoplastic masks, vac bags, and headrests are positioning aids used to reproduce the setup and prevent motion; the patient consents to them and could ask to be released. A restraint limits a patient's freedom of movement against their will and requires a physician order plus documentation. Calling a restraint an immobilizer does not remove exposure to a battery or false imprisonment claim.

Respondeat superior means 'let the master answer': the employer is liable for a therapist's negligent act committed within the scope of employment. Res ipsa loquitur means 'the thing speaks for itself' and is a rule of evidence: the injury so obviously arises from something under the defendant's control that negligence is presumed without proving specific acts. One assigns liability; the other shifts the burden of proof.

The portal of exit is how the pathogen leaves the reservoir, such as coughing, wound drainage, or blood. The portal of entry is how it reaches the susceptible host, such as broken skin, mucous membranes, or an IV or catheter site. They may involve the same body system but are separate links in the chain, and hand hygiene and PPE work by breaking the mode of transmission between them.

They protect the patient from the environment, not the environment from the patient, which is the reverse of standard isolation. Patients with treatment-induced neutropenia, common with concurrent chemoradiation or large marrow-bearing fields, need them. In practice: strict hand hygiene, no ill staff or visitors, no fresh flowers or raw produce, and disinfecting the couch and immobilization devices before the patient is set up.

Extravasation (infiltration) is contrast leaking into the surrounding soft tissue, producing immediate swelling, firmness, and burning, with possible tissue necrosis in severe cases. Phlebitis is inflammation of the vein itself and appears over hours to days as a warm, tender, reddened cord along the vessel. Both are local effects rather than systemic reactions: stop the injection, treat per protocol, and document.

Cerrobend contains bismuth, lead, tin, and cadmium. Heating it can release toxic cadmium and lead fumes, so the melting pot needs local exhaust ventilation, the safety data sheet must be accessible to staff, and scraps, filings, and dust are disposed of as hazardous waste. They never go into regular trash or down a sink drain, and hands are washed before eating.

The dose must first exceed a threshold (0.05 Sv effective dose equivalent, or 0.5 Sv to an organ, tissue, or skin) AND meet one of these: the total dose differs from the prescribed dose by 20% or more, the dosage falls outside the prescribed range, or a single fraction differs from its prescribed dose by 50% or more. The NRC rule governs byproduct material such as brachytherapy; most states apply comparable reporting rules to linac treatments.

Hyperfractionated courses require a minimum interfraction interval, commonly at least 6 hours, so that normal tissue can complete sublethal damage repair between fractions. If two fractions are delivered too close together, late-responding normal tissues absorb disproportionate injury. The recorded clock time is the documentary evidence that the required interval was honored.

Fraction number counts how many treatments have been delivered; elapsed days counts calendar days since the course began. The gap between the two exposes treatment interruptions. Because surviving tumor cells repopulate during a break, a course stretched well past its planned elapsed days can lose tumor control even though every prescribed fraction was eventually delivered.

The CBC flags myelosuppression through falling WBC and absolute neutrophil count, platelets, and hemoglobin, which is expected when large volumes of marrow are irradiated. PSA is a prostate tumor marker used to gauge disease burden and treatment response, not marrow status. BUN and creatinine assess renal function and are the values checked before iodinated contrast.

Compton scattering dominates throughout the megavoltage range. Its probability depends on electron density rather than on atomic number cubed as the photoelectric effect does. Bone and soft tissue therefore absorb megavoltage photons in roughly similar proportion, so bone is not preferentially overdosed. The same physics is why MV portal images look washed out compared with kV images.

Bremsstrahlung, or braking radiation, occurs when an incoming electron is decelerated and deflected by the target nucleus and releases a photon; it produces a continuous spectrum extending up to the electron's peak energy. Characteristic x-rays occur when an incoming electron ejects an inner-shell electron and an outer-shell electron fills the vacancy, emitting a photon of discrete energy. Megavoltage linac beams are essentially all bremsstrahlung.

Deterministic (tissue reaction) effects have a threshold below which they do not occur, and above it severity increases with dose. Examples are skin erythema, cataracts, sterility, and the acute radiation syndromes. Stochastic effects are assumed to have no threshold, and dose changes the probability of occurrence rather than the severity. Examples are carcinogenesis and heritable genetic effects.

TD5/5 is the dose producing a 5% incidence of a specified complication in a given organ within 5 years of treatment; TD50/5 is the dose producing 50% incidence within 5 years. These figures assume whole-organ irradiation, so treating only part of an organ generally permits a higher dose. That is why plan evaluation relies on dose-volume histogram constraints rather than a single tolerance number.

ARRT's content specifications state that SI units are the primary units of radiation measurement on this exam. Absorbed dose is the gray (Gy), dose equivalent and effective dose the sievert (Sv), exposure is coulombs per kilogram, and air kerma is the gray. Conversions worth memorizing: 1 Gy = 100 rad and 1 Sv = 100 rem, so a 2 Gy fraction equals 200 rad or 200 cGy.

Occupational: 50 mSv (5 rem) effective dose in a year, with a cumulative lifetime guide of 10 mSv multiplied by age in years. Public: 1 mSv (0.1 rem) in a year. These NCRP recommendations are mirrored in NRC 10 CFR Part 20. Both limits exclude natural background radiation and any medical exposure the individual receives as a patient.

0.5 mSv (0.05 rem) per month, with 5 mSv (0.5 rem) over the entire gestation. The limit applies only after a voluntary written declaration, so the declaration itself is the trigger, and it may be withdrawn in writing at any time. A second dosimeter is worn at waist level, beneath any protective apron, to monitor the fetal dose separately.

A primary barrier is any wall, floor, or ceiling the useful beam can be aimed directly at, so it must be the thickest. A secondary barrier is struck only by leakage radiation through the treatment head and by scatter from the patient and room, both far less intense, so it can be thinner. Because the gantry rotates, the primary barrier requirement follows every direction the beam can point.

A controlled (restricted) area has access limited and supervised for radiation-protection purposes, and it is occupied by trained, monitored workers to whom occupational limits apply. An unrestricted area is open to anyone, so exposure there is held to the public limit. This classification, combined with an assumed occupancy factor, drives both the required postings and the shielding calculation.

The ionization chamber is used for output calibration and absolute dosimetry because it responds proportionally to dose across a wide range and stays accurate in high-intensity beams. The Geiger-Muller detector is a highly sensitive count-rate instrument for locating low-level contamination or a stray source; it saturates and reads unreliably in an intense therapy beam, so it is never used to calibrate output.

It confirms that the visible light field the therapist aligns the patient to actually matches the radiation field being delivered, typically within a couple of millimeters (AAPM TG-142 uses 2 mm). If it fails, patients could be set up to a light field that misses part of the target or includes extra normal tissue. Do not treat: document the result and notify the medical physicist for correction.

A door interlock automatically terminates the beam when the vault door opens and blocks beam-on until it closes. It handles an anticipated, routine condition, and treatment can resume from where it stopped. An emergency off cuts power to the machine and is reserved for genuine emergencies such as a patient in danger or an imminent collision. It requires a full machine reset plus a service or physics check before treating again.

It provides an accurate, permanent, legally reportable record of accumulated dose, but only after processing at the end of the monthly or quarterly wear period. It cannot warn you in real time, so it never substitutes for time, distance, and shielding. It records dose only where it is worn, and it must never be shared, left in the beam, or taken home.

Ann Arbor staging is used for Hodgkin and non-Hodgkin lymphoma. It is built on which nodal regions are involved, whether disease sits on one or both sides of the diaphragm, and whether there is extranodal or splenic involvement. TNM (tumor, node, metastasis) is used for most solid carcinomas. Applying TNM to a lymphoma chart is a classic exam trap.

Grade (GX, G1 through G4) is a microscopic judgment of how well differentiated the cells are and how fast they proliferate, with G1 well differentiated and G4 undifferentiated or anaplastic. Stage describes anatomic extent: tumor size, nodal involvement, and metastasis. A small tumor can be high grade and a large one low grade. Grade comes from the pathology report; stage comes from imaging plus pathology.

They are defined by their relationship to the pectoralis minor muscle: Level I lies lateral to it, Level II lies behind it, and Level III lies medial to it in the infraclavicular region. Rotter's (interpectoral) nodes sit between pectoralis major and minor. This anatomy determines the superior border of a supraclavicular field and how high a tangential breast field must extend.

Neurologic loss from cord compression becomes permanent quickly, and the strongest predictor of walking afterward is whether the patient could walk when treatment began. Progressive back pain precedes weakness, a sensory level, and bladder or bowel dysfunction. Steroids are started immediately and radiation is simulated and begun urgently, often the same day, rather than deferred to the next routine slot.

Obstruction of the SVC by tumor or thrombus blocks venous return from the head, neck, and arms, producing facial and upper-extremity swelling, distended neck and chest veins, dyspnea, and facial plethora that worsen when the patient lies flat or bends forward. Most cases arise from right-sided lung cancer or mediastinal lymphoma. It is an oncologic emergency, and patients often need the head elevated for simulation and treatment.

Carcinomas arise from epithelium, meaning skin, glands, and the linings of organs, and account for most adult cancers; they typically spread first through lymphatics to regional nodes. Sarcomas arise from mesenchymal or connective tissue such as bone, cartilage, muscle, fat, and vessels, and typically spread hematogenously, often to lung, frequently bypassing nodes. That difference drives whether elective nodal volumes are treated at all.

Prostate cancer typically produces osteoblastic (bone-forming, sclerotic) metastases, most often in the lumbar spine and pelvis, spreading through Batson's vertebral venous plexus. This contrasts with the osteolytic, bone-destroying lesions typical of multiple myeloma and of renal and lung primaries. Osteoblastic lesions appear dense and white on radiographs and show increased uptake on bone scan.

The plan is calculated on the simulation geometry, so any difference between simulation and treatment becomes a systematic error repeated in every single fraction. A curved diagnostic couch changes the patient's external contour and position relative to the flat treatment couch. Same flat insert, same indexed headrest, same mask or vac bag, same arm position: reproducibility is the entire purpose.

A course runs for weeks, and ink or marker rubs off with clothing, perspiration, and washing; losing the reference points can force a re-simulation. Tattoos survive the course and remain available if re-treatment is ever needed, and they let the patient wash normally. Note that they mark the setup reference point, which is not the isocenter itself whenever a couch shift is applied.

The planning system converts CT numbers to relative electron density using a calibration curve measured for that specific scanner. That conversion drives the heterogeneity (inhomogeneity) correction, so dose through lung, bone, and air cavities is computed correctly. Two consequences: always use the scanner's own curve, and high-density artifacts from hip prostheses or dental work can corrupt the calculated dose unless the density is overridden.

Thinner slices produce sharper digitally reconstructed radiographs and more accurate contouring and volume definition, which matters most for small targets and steep dose gradients such as SRS and SBRT. The costs are more images, longer scan time, more contouring work, and higher image noise. Thicker slices scan faster but blur superior and inferior target boundaries and degrade DRR quality.

GTV is the gross tumor volume, meaning demonstrable disease visible on imaging or detectable on examination. CTV adds a margin around the GTV for suspected microscopic spread, including at-risk nodal regions, and is a clinical judgment. PTV adds a geometric margin to the CTV for setup variation and organ or patient motion, making it a planning construct rather than tissue. A PTV can therefore extend outside the patient's skin or into an organ at risk.

Beam intensity varies inversely with the square of the distance from the source, so I1/I2 = (d2 squared)/(d1 squared). Doubling the distance reduces intensity to one quarter. Practically, an extended-SSD setup for a large field requires an extended distance factor in the MU calculation, and in brachytherapy simply stepping back from the source is the cheapest protection available.

Percentage depth dose is used for fixed-SSD treatments, where the source-to-surface distance is constant and depth changes, so PDD already includes the inverse-square falloff with depth. TMR (tissue maximum ratio) is used for isocentric SAD treatments, where the isocenter stays at a fixed distance while depth changes with gantry angle. TMR has the inverse-square effect removed, so it depends only on depth and field size.

dmax is the depth of maximum dose and is set by beam energy, moving deeper as energy increases (roughly 1.5 cm for 6 MV and 2.5 cm for 10 MV). The buildup region above dmax is what gives megavoltage beams their skin sparing. Placing bolus on the skin moves the buildup region into the bolus, effectively shifting dmax to the surface and raising skin dose, which is exactly the goal for a superficial target such as a chest wall.

Use four times the area divided by the perimeter: equivalent square side = 4A/P = 2(L x W)/(L + W). A 10 x 20 cm field gives 4(200)/60 = 13.3 cm, so you look up output and PDD data for a 13.3 cm square field. The method works because scatter contribution, not field shape, determines the dosimetric data. For blocked fields, collimator scatter follows the open field while phantom scatter follows the blocked field.

Both are attenuation factors less than 1.0 because the wedge or block tray absorbs part of the beam, lowering the dose delivered per monitor unit at the calculation point. Since MU equals prescribed dose divided by output times all applicable factors, dividing by a factor below 1.0 increases the MU. Omitting the wedge factor from the calculation underdoses the patient; mounting the wrong wedge or leaving the tray off overdoses.

IMRT delivers intensity-modulated dose from a set of fixed gantry angles, repositioning the MLC at each angle. VMAT (volumetric modulated arc therapy) delivers continuously while the gantry rotates through one or more arcs, varying MLC leaf positions, dose rate, and gantry rotation speed simultaneously. Both rely on inverse planning. VMAT typically finishes faster using fewer monitor units, which shortens the window for intrafraction motion.

kV planar imaging gives the best bone and fiducial-marker contrast at the lowest imaging dose, making it the workhorse for daily 2D alignment. MV portal imaging uses the treatment beam itself, so it verifies the actual treated aperture and field shape, but with poor contrast. CBCT provides volumetric soft-tissue information for aligning to the target or to organs such as prostate, bladder, and rectum, at the highest imaging dose.

Electron beams deliver high surface dose followed by rapid dose falloff beyond the therapeutic range, sparing deeper tissue. Two useful planning rules of thumb: the 90% depth is roughly the energy in MeV divided by 3, and the practical range is roughly the energy divided by 2, both in centimeters of water. A 9 MeV beam therefore covers to about 3 cm. That sharp falloff is why electrons treat chest wall, scars, and skin overlying lung or spinal cord.

A physical wedge is a metal filter mounted in the head that attenuates one side of the field more than the other; it also hardens the beam and adds scatter. An enhanced dynamic wedge produces the same tilted isodose distribution by sweeping one collimator jaw across the field while the beam is on, with no physical attenuator. EDW avoids mounting errors and beam hardening, but because the wedge exists only in software, verify its orientation in the record and verify system.

Blocks are conventionally designed to transmit no more than about 5% of the primary beam, which takes roughly five half-value layers, since each HVL halves intensity and one half to the fifth power is about 3%. Going thicker yields diminishing benefit while adding weight plus a collision and drop hazard over the patient. MLC leaves are designed to a similar transmission goal, with interleaf leakage as the additional concern.

It compares the parameters actually set at the machine, including energy, monitor units, gantry and collimator angles, field size, accessories, and couch position, against the approved plan and blocks beam-on when they disagree. This catches transcription and setup-parameter errors. Its limitation is that it verifies against the data entered into it, so an error in the approved plan or in the original data transfer is faithfully repeated every fraction. It never replaces the initial physics chart check.

Respiratory gating delivers the beam only during a selected portion of the breathing cycle, typically end-expiration where position is most reproducible. Abdominal compression physically limits diaphragm excursion, shrinking the motion envelope. SGRT (surface guided radiation therapy) optically tracks the skin surface in real time to hold a breath-hold or trigger gating with no added imaging dose, which is why it pairs well with deep-inspiration breath-hold for left breast to move the heart out of the field.

The tattoos mark the reference point established at simulation, which is often not where the planner ultimately placed the isocenter. The plan therefore specifies a shift in centimeters along the lateral, longitudinal, and vertical axes to move from the marked reference point to the treatment isocenter. Applying a shift in the wrong direction offsets every fraction systematically, so the shift is checked against the plan and confirmed with imaging before the first treatment.

A diode taped to the patient's skin measures dose actually delivered during a real fraction, confirming that the intended entrance dose reached the patient with the correct energy, field, and accessories physically in place. A chart check only verifies numbers on paper. Diodes are typically used for the first fraction, for total body irradiation, and for complex or high-risk setups, and they need proper calibration and correction factors to mean anything.