RANZCR Rad Onc Anatomy flashcards

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

Conus medullaris level

In adults the spinal cord typically terminates at L1–L2. Below this level the lumbar cistern contains the cauda equina, which has a higher radiation tolerance than the cord.

Thecal sac contouring

The dural tube surrounding the cord and cauda equina. Cord dose constraints are usually reported as maximum dose to the thecal sac surface, often with a 1–2 mm geometric expansion.

Brachial plexus location

Formed by ventral rami C5–T1, passing between anterior and middle scalene muscles, lateral to the carotid sheath and medial to the humeral head. At risk in apical lung and supraclavicular fields.

Lumbosacral plexus formation

Formed by ventral rami of L1–S4. The lumbosacral trunk (L4–L5) crosses the pelvic brim medial to psoas, making it vulnerable during pelvic nodal irradiation.

Optic chiasm anatomy

Lies above and behind the sella turcica, formed by crossing nasal retinal fibres. It is a serial structure, so tolerance is defined by maximum rather than partial volume dose.

Optic nerve tolerance

Optic nerves and chiasm are serial organs. Maximum point dose is the relevant metric; conventional constraints are around 50–54 Gy in 2 Gy fractions, lower with hypofractionation or prior surgery.

Parotid gland lobes

The superficial lobe lies lateral to the retromandibular vein and masseter; the deep lobe lies medial to the vein. Mean parotid dose correlates with xerostomia after head and neck radiotherapy.

Submandibular gland position

Lies in the submandibular triangle, medial to the body of the mandible and lateral to the hyoglossus and mylohyoid muscles. Spared in contralateral neck irradiation to reduce xerostomia.

Waldeyer's ring

Lymphoid tissue ring of the nasopharynx, palatine tonsils, base of tongue, and oropharynx. Involved-site radiotherapy targets these regions plus involved neck node levels.

Neck node levels I–VII

Consensus surgical-radiological nodal levels used for head and neck contouring. Boundaries are defined by muscles, vessels, and bones; level II–IV are highest risk in most mucosal primaries.

Internal mammary nodes

Parasternal nodal chain lying 1–2 cm lateral to the sternal edge, deep to costal cartilages and intercostal muscles. Included in breast radiotherapy for high-risk axillary disease.

Breast tangent heart risk

Left anterior descending artery and left ventricle lie anteriorly adjacent to the chest wall. Left breast tangent radiotherapy increases cardiac dose, so deep inspiration breath hold is used to displace the heart.

Prostate zonal anatomy

Peripheral zone occupies the posterior and lateral gland, transition zone the centre. Most cancers arise peripherally. Rectum lies posterior and neurovascular bundles posterolateral, both dose-limiting.

Membranous urethra

Short segment passing through the urogenital diaphragm below the prostate apex. It is the principal dose-limiting structure for urinary toxicity in prostate radiotherapy, especially with dose escalation.

Rectum dose constraint

Anterior rectal wall lies immediately posterior to the prostate. Constraints are usually expressed as volume receiving a given dose (for example V60–V70), because rectal bleeding risk relates to irradiated volume.

Femoral head tolerance

Femoral heads lie lateral to the bladder and acetabulum. Constraints limit maximum dose to reduce avascular necrosis and fracture risk, especially in pelvic and anal cancer radiotherapy.

Sacral plexus and S2–S4

Sacral plexus lies on the piriformis and presacral fascia. It is at risk in presacral and sacral tumour radiotherapy; dose limits reduce lumbosacral plexopathy and sexual dysfunction.

Kidney tolerance

Kidneys are paired, parallel organs. Bilateral mean dose and volume constraints apply; in unilateral kidney irradiation the contralateral kidney must be spared, and dose is reported as mean and V20.

Liver tolerance

Liver is a parallel organ; dose is reported as mean liver dose minus gross tumour volume, plus volume receiving 30 Gy. Risk of radiation-induced liver disease rises with higher mean dose, especially in cirrhosis.

Lung dose metrics

Lungs are parallel organs; mean lung dose and V20 predict radiation pneumonitis. In thoracic radiotherapy both lungs minus gross tumour volume are contoured for dose reporting.

Oesophagus tolerance

Oesophagus lies anterior to the spine and posterior to the trachea, then enters the abdomen at T10–T11. Dose limits reduce stricture and perforation, especially with concurrent chemotherapy.

Heart substructures

Coronary arteries, valves, and ventricles receive different doses. For breast and lymphoma radiotherapy, mean heart dose and left anterior descending artery maximum dose are reported.

Pituitary fossa anatomy

Sella turcica of the sphenoid bone; pituitary lies within, with the stalk superiorly and cavernous sinuses laterally. Radiotherapy targets must spare optic chiasm and cranial nerves III–VI.

Cavernous sinus contents

Contains internal carotid artery and cranial nerves III, IV, V1, V2, and VI. Tumour extension here affects target volume and dose to cranial nerves during skull base radiotherapy.

Temporal lobe tolerance

Temporal lobes lie lateral to the middle cranial fossa and are at risk in nasopharyngeal and skull base radiotherapy. Volume receiving high dose correlates with temporal lobe necrosis.

Brainstem tolerance

Midbrain, pons, and medulla are serial structures. Maximum dose to brainstem surface is constrained (often around 54 Gy in 2 Gy fractions) to reduce cranial neuropathy and necrosis.

Cauda equina tolerance

Nerve roots in the lumbar cistern below the conus. Tolerance is higher than spinal cord; constraints are usually specified as maximum dose, typically around 60 Gy in 2 Gy fractions.

Bladder dose constraint

Bladder lies anterior to the uterus and vagina and superior to the prostate. Constraints limit volume receiving high dose to reduce urgency and cystitis; a comfortably full bladder displaces bowel.

Small bowel tolerance

Small bowel is a serial-parallel hybrid organ. Volume receiving 15 Gy and maximum dose predict acute and late toxicity; bowel displacement techniques reduce irradiated volume in pelvic radiotherapy.

Anal canal anatomy

Anal canal extends from anorectal junction to anal verge, surrounded by internal and external sphincters. Sphincter-preserving dose limits reduce incontinence after chemoradiotherapy for anal cancer.

Inguinal nodes

Superficial inguinal nodes lie in the femoral triangle below the inguinal ligament; deep nodes lie medial to the femoral vein. At risk in anal, vulvar, and distal lower limb malignancies.

Bone marrow sparing

Active marrow in pelvic bones and lumbar spine is a parallel organ. Contouring and dose-volume constraints reduce haematological toxicity during pelvic chemoradiotherapy.