RANZCR Rad Onc Anatomy key terms

The visible or palpable extent of malignant disease, defined from imaging, examination or surgical findings before any treatment. It is the starting point for target volume delineation and excludes microscopic spread.

A volume containing the GTV plus any region of suspected subclinical microscopic disease that must be treated. It is a biological and anatomical concept, independent of beam arrangement or patient set-up.

A geometrical margin added around the CTV to account for organ motion, set-up variation and treatment delivery uncertainties, ensuring the prescribed dose actually reaches the CTV.

A volume encompassing the CTV plus an internal margin that compensates for physiological movement such as respiration, swallowing or bladder filling, measured relative to an internal reference point.

The additional margin around the ITV or CTV that accounts for uncertainties in patient positioning, immobilisation, and day-to-day reproducibility of treatment delivery on the machine.

Normal tissues whose radiation sensitivity may significantly influence treatment planning or prescribed dose, because exceeding their tolerance risks clinically important toxicity.

A margin added around an organ at risk to account for its motion and set-up uncertainty, analogous to the PTV, so that dose constraints are respected despite geometric variation.

A graphical or numerical summary relating dose to the volume of a structure receiving that dose, used to assess target coverage and organ-at-risk constraints during plan evaluation.

The radiation dose to a normal tissue above which the risk of a defined complication rises to an unacceptable level, conventionally expressed with a specified endpoint and fractionation.

The point in space about which the gantry, collimator and couch rotate, and where their axes intersect. Accurate alignment of the isocentre with the target is central to precision radiotherapy.

Equipment such as thermoplastic masks, vacuum bags or bite blocks used to hold the patient in a reproducible position, reducing set-up uncertainty and allowing smaller planning margins.

A CT acquisition that records images throughout the respiratory cycle, allowing tumour motion to be characterised and an internal target volume or gating window to be defined.

A treatment delivery technique in which the beam is switched on only during a selected portion of the breathing cycle, reducing the volume of normal tissue irradiated by moving targets.

Radiotherapy delivered by radioactive sources placed inside or close to the tumour, giving a high local dose with rapid fall-off and sparing of distant normal tissues.

A device inserted into a body cavity or tissue to hold radioactive sources in a predetermined geometry for brachytherapy, such as a tandem and ring or a vaginal cylinder.

A defined anatomical or geometric reference point at which the brachytherapy dose is stated, such as point A for cervical treatment, allowing reproducible prescription and reporting.

Surgically and radiologically defined nodal groups (levels I to VI, plus the retropharyngeal and parotid groups) that guide elective nodal irradiation and neck dissection in head and neck cancer.

A ring of lymphoid tissue at the entrance to the pharynx comprising the nasopharyngeal tonsil, palatine tonsils, lingual tonsil and lateral pharyngeal bands, a common site of lymphoma and carcinoma.

The largest salivary gland, lying in front of and below the ear, whose superficial lobe is closely related to the facial nerve and is a dose-limiting structure in head and neck radiotherapy.

The seventh cranial nerve, exiting the skull through the stylomastoid foramen and dividing within the parotid gland into temporal, zygomatic, buccal, marginal mandibular and cervical branches.

The eleventh cranial nerve, which descends through the posterior triangle of the neck and supplies trapezius and sternocleidomastoid; it is at risk during level V nodal irradiation or dissection.

Dryness of the mouth resulting from reduced salivary flow, a predictable late effect of irradiating the major salivary glands and a key constraint in head and neck treatment planning.

A network of nerve roots from C5 to T1 that passes between the anterior and middle scalene muscles and beneath the clavicle, a dose-limiting structure in apical lung and supraclavicular irradiation.

Anatomically defined groups of mediastinal and hilar lymph nodes, numbered by the IASLC system, used to describe disease extent and to define nodal target volumes in thoracic radiotherapy.

The trachea is the cartilaginous airway extending from the larynx to the carina, where it divides into main bronchi; the carina is a key landmark for central lung tumours and mediastinal nodal levels.

A muscular tube running from the pharynx to the stomach through the posterior mediastinum, closely related to the heart, aorta and spine, and a dose-limiting organ in thoracic radiotherapy.

The central nervous system structure within the vertebral canal, running from the medulla to the conus medullaris, and the most critical dose-limiting organ in most radiotherapy plans.

The bundle of lumbar and sacral nerve roots descending below the conus medullaris within the thecal sac, at risk during lumbar or sacral irradiation.

A fibromuscular gland below the bladder surrounding the proximal urethra, divided into peripheral, central and transition zones, and the commonest target in pelvic radiotherapy.

Paired glands posterior and superior to the prostate that contribute seminal fluid; their involvement determines risk grouping and whether they are included in the prostate target volume.

The collection of cavernous nerves and vessels running posterolateral to the prostate, whose damage or excessive irradiation contributes to erectile dysfunction after treatment.

The distal large bowel extending from the rectosigmoid junction to the anal canal, lying posterior to the prostate and vagina and a principal dose-limiting organ in pelvic radiotherapy.

The terminal portion of the gastrointestinal tract from the anorectal junction to the anal verge, containing the internal and external sphincters and the target of definitive chemoradiotherapy for anal cancer.

Superficial and deep nodal groups in the groin draining the lower limb, perineum and distal anal canal; the superficial group lies along the inguinal ligament and great saphenous vein.

The proximal articulation of the femur with the acetabulum, a critical dose-limiting structure in pelvic radiotherapy because excessive dose causes avascular necrosis and fracture.

A muscular tube carrying urine from the renal pelvis to the bladder, running anterior to the psoas and crossing the pelvic brim, where it may be inadvertently included in pelvic target volumes.

The anatomical subdivision of the breast into four quadrants plus the axillary tail of Spence, which determines tumour location, surgical approach and which nodal basins require treatment.

Three surgical levels defined by relation to the pectoralis minor: level I lateral, level II posterior and level III medial to it, guiding axillary dissection and regional nodal irradiation.

A large chest wall muscle inserting onto the humerus, forming the anterior axillary fold and an important landmark for breast target volume delineation and for level I axillary nodes.