HPTC RT Exam key terms

A radiation protection principle meaning doses are kept As Low As Reasonably Achievable, accounting for economic and social factors. It guides shielding design, workload planning, and daily choices about imaging and treatment techniques.

A planned upper limit on dose or dose-volume metrics for an organ at risk, used during optimization and plan review. Constraints are planning goals, not guarantees, and are distinct from regulatory dose limits for workers and public.

A design computation estimating transmitted dose through barriers from workload, use factor, occupancy factor, and distance. It determines required primary and secondary barrier thickness for treatment rooms and imaging spaces.

The machine output per week, usually expressed in Gy or cGy at a reference distance, used in shielding calculations. It reflects patient volume, prescription dose, and techniques such as intensity modulation that increase monitor units.

The three basic methods for reducing occupational radiation exposure: minimize time near sources, maximize distance, and use appropriate barriers. Distance is especially powerful because exposure falls with the inverse square of separation.

A relationship stating that radiation intensity from a point source decreases in proportion to the square of the distance from that source. It underpins room design, source handling, and safe standing distances.

A badge or electronic device worn to record occupational dose, commonly a film, optically stimulated luminescence, or thermoluminescent badge. It is worn at a specified body location and exchanged on a defined schedule for dose records.

A tissue-weighted sum of equivalent doses across organs, intended to express overall stochastic risk from a non-uniform exposure. It is used for occupational and public dose reporting, not for predicting individual outcomes.

The planning session in which the patient is positioned, immobilized, and imaged in the treatment posture so that planning images match treatment geometry. It establishes reference marks, isocenter, and the coordinate system used downstream.

Equipment such as thermoplastic masks, vacuum cushions, or head frames that limits patient motion and reproduces position between sessions. Its index and fit must be documented because reproducibility directly affects planning margins.

The point in space about which the treatment unit, collimator, and couch rotate, and to which the plan is referenced. Patient setup aims to align the target reference point with this machine point.

A deviation between the intended and actual patient position at treatment, whether systematic or random. It is measured by imaging and absorbed into planning margins such as the planning target volume margin.

A geometric volume that adds a margin around the clinical target volume to account for setup variation and internal organ motion. It is a planning construct, not a visible tumor boundary.

The volume containing the demonstrable tumor plus any region of suspected microscopic spread that must receive a specified dose. It sits inside the planning target volume margin.

The visible or palpable extent of tumor as determined by imaging and clinical examination. It is the innermost target volume and does not include microscopic spread or geometric margins.

Normal tissue whose radiation tolerance may limit the achievable dose distribution, such as spinal cord, parotid glands, or rectum. Its constraints shape optimization and plan evaluation.

A cumulative plot showing the fraction of a structure's volume receiving at least a given dose. It summarizes plan quality for targets and organs at risk and supports comparison of competing plans.

The documented set of beam geometries, energies, fluences, and calculations that delivers the prescribed dose to targets while respecting normal tissue constraints. It is reviewed, approved, and transferred to the treatment unit.

A display of anatomy and structures projected along the beam direction from the source's perspective. It helps choose gantry and collimator angles that avoid critical structures.

The use of imaging at simulation or before treatment, such as cone-beam CT, kV planar, or ultrasound, to verify and correct patient position. It reduces setup uncertainty and supports smaller margins.

Correction of translational offsets along three axes plus rotational offsets about those axes, typically via a robotic couch. It permits precise alignment when rotational error would otherwise shift the target.

The machine output unit calibrated so that a defined number corresponds to a known absorbed dose under reference conditions. Prescriptions are converted to monitor units by treatment planning calculations.

The process establishing the relationship between machine monitor units and absorbed dose at a reference point under reference conditions. It is traceable to a standards laboratory and verified by periodic quality assurance.

A planned program of tests and reviews confirming that equipment, software, and processes perform within specified tolerances. It includes daily, monthly, and annual checks plus independent verification of plans.

A full workflow check from imaging and planning through delivery and measurement on a phantom. It verifies that the integrated system produces the intended dose before complex techniques are used clinically.

A set of computer-controlled tungsten leaves that shape the beam aperture and can move during delivery to modulate fluence. Leaf positioning accuracy and transmission are important quality assurance targets.

A delivery technique in which beam fluence is varied across the field, often with inverse planning, to create concave dose distributions. It increases monitor units and demands rigorous verification and imaging.

An optimization approach that starts from desired dose objectives and constraints and computes fluence or machine parameters that best satisfy them. It contrasts with forward planning, where parameters are set and dose is then calculated.

The measurement and calculation of absorbed dose in tissue and phantoms, using devices such as ionization chambers, diodes, and film. It links machine output, plan calculations, and patient delivery.

A detector that measures charge produced by radiation ionizing gas, calibrated to give absorbed dose under specified conditions. It is the reference instrument for machine calibration and many quality assurance measurements.

Dose measurement performed on or in the patient during treatment, often with diodes or film, to confirm delivered dose. It can catch errors such as calculation mistakes or setup problems in real time.

The set of checks confirming that the planned parameters and dose match what is delivered, including chart review, imaging, and independent dose calculation. It is a barrier against misadministration.

Division of a total radiation dose into multiple smaller treatments over days or weeks. It exploits differences in repair and repopulation between tumor and normal tissue to improve the therapeutic ratio.

The balance between tumor control probability and normal tissue complication probability achieved by a treatment approach. Improving it means raising tumor kill while limiting toxicity.

A modeled estimate of the likelihood that a normal structure will suffer a specified complication at a given dose or dose-volume. It informs constraints and plan comparisons.

A modeled estimate of the probability that a tumor is eradicated at a given dose. It rises with dose and is weighed against normal tissue risk in plan evaluation.

The study of how ionizing radiation interacts with living tissue, including DNA damage, repair, cell survival, and tissue responses. It underpins fractionation schedules and tolerance limits.

Side effects appearing during or shortly after radiotherapy, such as skin reaction, fatigue, or mucositis, typically related to dose per fraction and treated tissue. They are usually reversible and require monitoring and supportive care.

Complications emerging months to years after treatment, such as fibrosis, stricture, or second malignancy, often related to total dose and fraction size. They are generally irreversible and guide normal tissue constraints.

Systematic evaluation of a patient's condition, symptoms, and response before, during, and after treatment. It includes history, skin and symptom checks, weight, and documentation that informs plan adjustments or referrals.

A patient's voluntary agreement to a procedure after receiving understandable information about purpose, risks, benefits, and alternatives. It must be documented and may be withdrawn at any time.

The obligation to protect identifiable health information and physical dignity, limiting access to those with a clinical need. It covers records, images, conversations, and treatment areas.

The limits of an appropriate therapeutic relationship, avoiding personal, financial, or romantic involvement that could exploit the patient's vulnerability. Boundary crossings are documented and reflected upon.

The range of duties a professional is legally and ethically permitted to perform given licensure, training, and institutional policy. Working outside it requires supervision or referral.