Medical Physics Dictionary

Ablation: Removal or excision. Ablation is usuallycarried out surgically.

Acoutstic Neuroma: A benign tumor that may develop on thehearing and balance nerves near the inner ear. Can betreated by Stereotactic RadioSurgery (SRS).

Adipose: Fat, but usually refers specifically to tissuemade up of fat cells, such as yellow layer of fatbeneath skin.

Adjuvant Chemotherapy: Given to prevent growth of stray cancer cells remaining in the body after surgery or radiation.

Alopecia: Hair loss.

Ampulla of Vatar: An enlargement of the ductsfrom the liver and pancreas where they enter the small intestine.

Angiogenesis: The growth of blood vessels causedby cancer.

Apparent Activity: The activity of a *bare point source*of the same nuclide that produces the same exposurerate at one meter as the source to be specified. Determinedby dividing the the measured exposure rate at one m by theexposure rate constant of the unfiltered source at one m.

Apodization: Literally 'removing the foot'. A technical termfor changing the shape of a mathematical function or electricalsignal. e.g., in optics, simulation of a gaussian laser beam input profile is an example of apodization

Arteriovenous Malformation: A congential disorder ofblood vessels in the brain, brainstem, or spinal cordthat is characterized by a complex, tangled web of abnormal arteries and veins connnected by one ormore fistulas.

AT - Ataxia Telangiectasia: A neurodegenerative genetic disease characterized by cerebellar ataxia (lack ofbalance). People with AT are predisposed to leukimia andlymphoma and are extremely sensitive to radiation.

Axilla: The cavity beneath the junction of the arm and the body, better known as the armpit.

Bleb: A bladder-like structure more than 5mm in diameterwith thin walls that may be full of fluid. Also calleda bulla.

Blood: Arterial blood transfers oxygen and nutrientsto tissues. Venous blood transfers carbon dioxide andmetabolic by-products to lungs and kidneys.

Brachial Plexus: A network of nerves formed by cervicaland thoracic spinal nerves located in neck and axilla.

Brachytherapy: Radiation treatment given by placing radioactive material directly in or near the target, which is often a tumor. Brachytherapy for prostate cancer, for example, is also called interstitial radiation therapy or seed implantation. In brachytherapy for prostate cancer, radioactive seeds are implanted in the prostate. The seeds might be titanium-encased pellets containing the radioisotope iodine-125. "Brachy-" is Greek for "short." The opposite of brachytherapy is teletherapy, treatment in which the radiation source is at a distance from the target.

C1-C7: The upper 7 cervical (neck) vertebrae. Thetop one, C1, is called the atlas. Named afterGreek god that held earth on shoulders.

Carina: A ridgelike structure.

-Cauda Equina: Bundle of nerves at the base of the spinal cord. So named because they resemblethe tail of a horse.

Caudal: Anatomic term meaning pertaining to thetail or hind part.

Cephal - Prefix indicating the head.

Chondrosarcoma - Type of bone cancer. Found mainly in adults. This type of tumor forms in cartilage, the rubbery tissue around joints.

Coronal: A coronal plane through the body is a vertical plane from head to foot and parallel to the shoulders.

Circle of Willis: A joining of arteries(anastomosis) at the base of the brain.

Cytotoxic: Cell killing.

Dehisce: To burst open or gape.A surgical wound may dehisce.

De novo: New. e.g., a mutation in the DNAcan be 'de novo', meaning it has occurredin the first generation.

Dysphagia: Difficulty in swallowing.

Dyspnea: Difficulty breathing or shortness of breath.

Edema: Swelling. e.g., tumor edema.

Embolization: A treatment that clogs small blood vesselsand blocks the flow of blood, such as to a tumor.

Endogenous: Inside. e.g., endogenous cholesterol is thatmade inside the body, as opposed to the diet.

Epidemiology: The study of populations to determine diseaseorigin.

Equivalent Uniform Dose: The homogenous dose distribution whichproduces the same surviving fraction of clonogenic cells as thatobtained with an inhomogenous dose distribution.

Etiology: Cause of disease.

Exthophthalmos: Increase of volume of the tissue behindthe eye, resulting in appearance of eyes bulging out offace.

FDG - Fluoro-Deoxy-Glucose: Active emitter in many PET scans.

Fossa: An anatomical pit, groove or depression.

Glioblastoma Multiforme - Type of tumor that forms fromglial (supportive) tissue in brain. Highly malignant, grows quickly.

In Silico: Performed on computer or via computer simulation

Infarct: An area of tissue death due to lack of oxygen.

Inferior - Below or downward. Antonym - Superior.

Ipsilateral - On the same side. The opposite of contralateral.e.g., a tumor involving the right side of the brain may affectvision ipsilaterally (i.e., in the right eye).

Glioma: A brain tumor that begins in glial or supportive cell in the brain. Malignant gliomas are the most commonfrom of cancer in the central nervous system (brain andspinal cord) and often have a poor prognosis.

Gray - Symbol: Gy. The derived SI unit of absorbed dose of ionizing radiation and of specific energy imparted. It is equal to an absorptionor delivery of one joule per kilogram of irradiated material. It replaces the rad. 1 gray = 100 rad.

Histology - The study of form of structures seen underthe microscopy. e.g., from a biopsy.

Hemiparesis - Weaknes on one side of the body.

--Hounsfield Unit: Units of density for CT numbers. -1000HU = air, 0HU = H2O, +1000HU = bone. So a change of 1HU corresponds to a change of0.1% of attenuation coefficient between waterand air.

Ilium: The upper part of the bonypelvis that forms the receptacle ofthe head of the femur at the hip joint.

--In situ: In the normal location. An "in situ" is one that is confined to its site of origin and has not invaded neighboring tissue or gone elsewherein the body.

In vivo: In the living organism.

In vitro: In the laboratory.

Intrahepatic: Within the liver. -

Isocenter: A point of intersection of the collimatoraxis and the gantry axis of rotation.

KERMa: Acronym - Kinetic Energy Released in the Medium. The quotient of dE_tr by dm. The unit for kerma is the same as for dose, i.e., J/kg.

L1-L5: The five lumbar vertebrae situated between thethoracic vertebrae and the sacral vertebrae in the spinalcolumn.

Longitudinal Study: A study done over the passage oftime.

Macula: Spot. In the retina, the macula is the spotwhere the center of images are focused.

Medial: The side of the body or body part that is nearer to the middle or center of the body. Antonymn - lateral.

Mediastinum: The area between the lungs. The organs in thisarea include the heart and its large veins and arteries,the trachea, the esophagus, the bronchi and lymph nodes.

-Metastasis: The very important process by which cancer spreads from one part of the body to another, the way it travels from the place at which it first arose as a primary tumor to distant locations in the body. The term "metastasis" also applies to a tumor that crops up by this process due to the spread of the primary tumor. For example, someone with melanoma may have a metastasis in their brain. And a person with colon cancer may fortunately show no metastasis. Cells that metastasize are basically of the same kind as those in the original tumor. So, if the cancer arose in the lung and metastasized to the liver, the cancer cells growing in the liver are lung cancer cells. The ancient Greeks used the word metastasis to mean "removal from one place to another." The plural of "metastasis" is "metastases."

Morbidity: Illness, disease.

Mortality: A fatal outcome or, in one word, death. The word 'mortality' is derived from 'mortal' which came from the Latin 'mors'(death).

Murine: Rat or mice.

-Neoadjuvant Chemotherapy: May be used to shrink alarge tumor prior to surgical resection, or to betreated more effectively with radiation.

Neoplasia: The process of abnormal and uncontrolledgrowth of cells. The product of neoplasia is a neoplasm(a tumor).

Nidus: Latin word for nest. Any structure that resemblesa nest in appearnce. e.g., AVM. pl - nidi.

-NTCP: Normal Tissue Complication Probability.

Occult: Hidden.

Optic Chiasm: Crossing of the optic nerves.

Orthotopic: In the normal or usual position.

-Os: The mouth or upper opening of the digestive tract.Any opening or aperature in the body.

-Osseous - Having to do with the bone, consisting of bone or resembling bone. From "os" which is a synonym for "bone." The Latin word "os" means "bone"as does the related Greek word "osteon."

Palliative care: 1) Medical or comfort care that reduces the severity of a disease or slows its progress rather than providing a cure. For incurable diseases, in cases where the cure is not recommended due to other health concerns, and when the patient does not wish to pursuea cure, palliative care becomes the focus of treatment. For example, if surgery cannot be performed to remove a tumor, radiation treatment might be tried to reduce its rate of growth, and pain management could help the patient manage physical symptoms. 2) In a negative sense, provisiononly of perfunctory health care when a cure is possible.

Parenchyma: Key elements of an organ to its functioning,as distinct from the capsule that encompasses it, or othersupporting structures. e.g., the parenchyma of the testisare the seminferous tubules.

Parenteral: Not in or through the digestive system.

Parotid gland: The largest of the three major salivary glands, it is located in front and below the ear and behind the jaw bone. The other two glands are the submandibular(submaxillary) and sublingual.

Perfusion: Flowing over or through. Blood flow through the organs and tissues.

---Plexus: Network or tangle of lymphaticvessels, nerves or veins. e.g., brachialplexus network of nerves leading tothe arm.

---Portal Vein: A large vein that caries blood from thestomach and intestines to the liver.

Prone - Lying face downward.

Prophylactic - Prevenative measure.

Resection - Surgical removal of part of an organ.

Restenosis - reclosing of an artery after, e.g., angioplasty.

S1-S5: The five sacral vertebrae situated below the lumbar vertabrae and above the coccyx, which is thelowest segment of the vertebral column.

Sacrum: The large heavy bone at the base of thespine made up of fused sacral vertebra. Located between the lumbar vertebrae and the coccyx. Roughlytriangular in shape and makes up back wall of pelvis.Wider in females.

---Sagittal: A vertical plane passing through the body which divides it into left and right sides.

Sarcoma: One of a group of tumors usually arisingfrom connective tissue. Most sarcomas are malignant.Many types are named after the type of cell, tissueor structure involved such as angiosarcoma, chondrosarcoma,etc.

Seminal Vesicle: Structure in male about 5cm longand located behind bladder and above prostate.Contributes fluid to the ejaculate.

Sensitivity: (true-positives)/(true-positives + false-negatives).A number close to 1 is desirable.

Sequela - A pathological condition resulting from a prior disease.

Sinogram: Image representation of raw data obtained whenprojection reconstruction is used.

Specificity: (true-negatives)/(true-negatives + false-positives).A number close to 1 is desirable.

Squamous cell carcinoma: Cancer that begins in squamous cells -- thin, flat cells that look under the microscope like fish scales. The word "squamous" came from the Latin squama meaning "the scale of a fish or serpent." Squamous cells are found in the tissue that forms the surface of the skin, the lining of the hollow organs of the body, and the passages of the respiratory and digestive tracts so squamous cell carcinomas may arise in any of these tissues.

Stereotactic - Precise positioning in threedimensional space. e.g., a biopsy, surgery orradiotherapy can be performed stereotactically.

Stereotactic radiotherapy: Radiation therapy in which a number of precisely aimed beams of ionizing radiation coming from different directions meet at a specific point, delivering the radiation treatment to that spot.

Sulcus - Any of the narrow fissures separating convolutions of the brain. pl - sulci

Superior - Above. Antonym - Inferior.

Supine - Lying on the back.

Surrogate Marker: An indirect indicator of something, suchas measuring viral load to assess the treatment effect ofa drug.

Synovectomy - Removal of the synovial membrane locatedin joints. Treatment for arthritis.

Syncope - fainting.

T1-T12: The twelve thoracic vertabrae situated betweenthe cervical (neck) vertabrae and the lumbar vertabrae.They provide attachment points for the ribs.

Vaginal Fornix: The anterior and posterior recesses into whichthe upper vagina is divided. Fornix is Latin for vault.Ovoids often are placed into these during Tx for cervicalcancer.

Wilms Tumor: A cancer of the kidney. One of the most importantmalignancies of childhood, due to loss or inactiviation of atumor suppressor gene called WT1 on chromosome 11.

Xenograft: A surgical graft from one species to an unlikespecies. e.g., from a human breast tumor to mice.

I obtained many of the above definitions at Note: If a mistake or inconsistency is noticed here, please notify Lars Ewell: