Patient Data Acquisition and Simulation in Radiotherapy

Flashcards covering core vocabulary terms, simulation processes, and ICRU volume definitions from the Physics of Radiotherapy lecture notes.

Radiotherapy

A medical treatment where ionizing radiation is used to kill cancer cells.

Goal of Radiotherapy

Maximizing tumor control while minimizing dose to healthy tissue, thereby achieving a high tumor control probability (TCP) at a low risk of normal tissue complications (NTCP).

Tumor Control Probability (TCP)

The probability or likelihood of achieving local control of a tumor using radiation therapy.

Normal Tissue Complication Probability (NTCP)

The probability or risk of inducing complications in healthy normal tissue surrounding a tumor during radiation therapy.

TCP vs. NTCP Relationship

Sigmoid curves demonstrating that increasing the radiation dose increases the probability of tumor control (TCP), while also increasing the probability of normal tissue complications (NTCP).

External Radiotherapy

A technique where a machine outside the patient's body directs beams of radiation directly at the cancer.

Internal Radiotherapy (Brachytherapy)

A technique where a radioactive source or implant is positioned inside the patient's body near or within the cancer.

Radiotherapy Process Steps

The clinical patient care pathway in radiotherapy, consisting of Consult, Imaging/simulation, Treatment planning, Treatment delivery, and Follow-up, supported throughout by Quality assurance.

Radiotherapy Simulator

A machine consisting of a diagnostic x-ray tube mounted on a rotating gantry to simulate the geometries of isocentric linacs, delivering diagnostic-quality x-ray beams suitable for treatment planning systems (TPS) rather than megavoltage treatment beams.

CT Simulator

A specialized CT scanner equipped with a flat table top, laser marking system, and virtual simulation software dedicated to radiotherapy planning and target localization.

Physical Simulation

The physical steps on a CT simulator involving acquisition of the patient data set, localization of the target and adjacent structures, and definition and marking of the patient coordinate system.

Virtual Simulation

Software-based planning steps on a CT simulator involving treatment field design, data transfer to the Treatment Planning System (TPS), and production of images used for treatment verification.

Digitally Reconstructed Radiograph (DRR)

A digital equivalent of a planar simulation x-ray film generated from a CT data set using virtual simulation software, used for comparison with portal images to verify patient setup and beam arrangement.

Immobilization Devices

Equipment designed to restrict patient motion during treatment and ensure precise reproduction of the patient position across simulation and all treatment fractions.

Head Rest

The simplest immobilization device in radiotherapy, contoured to fit snugly under the head and neck area for comfortable patient positioning on the couch.

Treatment Planning System (TPS)

Computerized systems used in external beam radiation therapy to model beam shapes and calculate dose distributions in order to maximize tumor control and minimize normal tissue damage.

ICRU Volume Definitions

Standardized volume concepts defined by the ICRU for 3D treatment planning, including Gross Tumor Volume (GTV), Clinical Target Volume (CTV), Internal Target Volume (ITV), Planning Target Volume (PTV), and Organ at Risk (OAR).

Gross Tumor Volume (GTV)

The gross palpable, visible, or demonstrable extent and location of malignant growth as determined by clinical examination and imaging modalities.

Clinical Target Volume (CTV)

The tissue volume containing a demonstrable GTV and/or sub-clinical microscopic malignant disease that must be eliminated, typically specified as a margin around the GTV.

Internal Target Volume (ITV)

The volume consisting of the CTV plus an internal margin designed to account for variations in size, shape, and position of the CTV due to internal organ movement.

Planning Target Volume (PTV)

A geometrical volume concept defined to select appropriate beam arrangements, incorporating margins for setup uncertainties, machine tolerances, and intra-treatment variations to ensure the prescribed dose is absorbed in the CTV.

Organ at Risk (OAR)

An organ whose sensitivity to radiation is such that the delivered dose from a plan may approach its tolerance limit, requiring modifications to beam arrangement or prescribed dose.

ICRU Reference Dose Point

A specified point located in an area of accurate dose calculation within the central part of the PTV (typically the isocenter in multi-field plans) used to characterize the delivered dose.