Quality assurance in radiation therapy: physical aspects.

The present status of the quality assurance work regarding the physical aspects in radiation treatments is discussed. In particular, the situation in Europe is surveyed. An analysis of the errors in the delivered absorbed dose to a specified point in the irradiated patient shows that the uncertainty, to approximately the same degree, depends on the dose distribution determination, the dose planning and the patient irradiation. Following the procedure generally in use, the overall uncertainty will be about 8%. The random uncertainties are estimated as one standard deviation and non-random uncertainties to corresponding degree of uncertainty. It is argued that this level must be improved. Furthermore, dose intercomparisons show that in reality much larger errors occur in clinical practice. Different means to improve this situation are discussed.