title: Quality assurance and radiotherapy.
abstract: As mentioned in several chapters of this report, administering the radioactive dosage requires a high level of precision. Demands on precision dosimetry have increased with modern curative radiotherapy. A few percent increase or decrease in the dose level may, in some cases, represent the difference between successful and unsuccessful therapy (Chapter 10). High precision is therefore required of basic dosimetry for different types and qualities of radiation, and in applied dosimetry for, eg, dose planning and in vivo dosimetry. External audits should be used to avoid systemic error. Comparative dose measurements are important, both to establish variations within a department and between departments. Simulators and/or therapeutic equipment should be checked regularly to assure that the direction of the radioactive beam and the field size complies with the plan. Margins that are too narrow can miss part of the target volume and increase the risk for relapse. If, on the other hand, the margins are too wide, the reaction to radiation in nearby organs at risk may be unacceptable. Accessible field control images should therefore be integrated in regular routines, at least when the margins between tumors and risk organs are small.
mesh_terms: D006801:Humans; D009369:Neoplasms / Q000532:radiotherapy*; D011785:Quality Assurance, Health Care; D011878:Radiotherapy / Q000592:standards