A distributed source is a one dimensional area or volume source compared to the dimensions of the detector and which may produce a radiation beam over a wide range of angles of incidence on the measurement area.

Dosage is an important factor in the use of ionization radiation as well as in application of contrast agents or radiopharmaceuticals and the dosage should be comply with the ALARA principle (As Low As Reasonably Achievable).
Ionizing radiation comes from natural and artificial sources. Radiation effects depend on the type of radiation, and various units are used for measurement of dosages including gray, sievert, radiation absorbed dose (RAD), roentgen equivalent in man (REM), and roentgen. The amount of radiopharmaceutical given to a patient is measured in becquerels (Bq).
The dosage of contrast media in radiographic or computer-tomographic procedures should be tailored according to the diagnostic indications, the iodine concentration, and the patient's body size and age.

See also Administrative Dose Guidelines.

In radiology dose is the term for radiation related to the amount of energy absorbed in matter (for example absorbed dose, acute dose, effective dose, external dose, personal dose and committed dose equivalent). The SI standard unit of radiation dose is the gray.
Dose refers also to the amount of medication, radiopharmaceutical or contrast medium used in diagnostic imaging.

See also Deep Dose Equivalent, Critical Organ, Eye Dose Equivalent, Collective Effective Dose, Medical Internal Radiation Dose Committee, and Chronic Dose.

The dose limit is the highest value of an applied or allowed radiation exposure. The radiation dose is limited in order to prevent the occurrence of radiation-induced deterministic effects or to limit the probability of radiation-related stochastic effects to an acceptable level.

See also Whole Body Counter, Thermoluminescent Dosimeter, Dosimetrist, Annual Limit On Intake, Committed Effective Dose Equivalent, Computed Tomography Dose Index, Directional Dose Equivalent, Doubling Dose.

Dosimetrists calculate the dose of radiation. To secure sufficient tumor destruction while sparing the normal tissues, a number of (often) complex treatment plans are developed.
The Medical Dosimetrist Certification Board certifies dosimetrists. Dosimetrists work with the physician and the medical physicist to choose the treatment plan that is best for each patient. A dosimetrist may start as a radiation therapist and become with intensive training a dosimetrist. Others are graduates of dosimetry programs.